Allergic contact dermatitis

ARTICLE

Auteur(s) :, Pierre SAINT-MEZARD¹, Aurore ROSIERES¹, Maya KRASTEVA¹, Frédéric BERARD^1,3, Bertrand DUBOIS², Dominique KAISERLIAN², Jean-François NICOLAS^1,3,*

¹INSERM U 503, IFR 128 Bioscience Lyon-Gerland, 21, avenue Tony Garnier 69007 Lyon
²INSERM U 404, IFR 128 Bioscience Lyon-Gerland, 21, avenue Tony Garnier 69007 Lyon
³Clinical Immunology and Allergy Unit, CH Lyon-Sud, 69495 Pierre-Benite Cedex, France.
^*J.F. Nicolas, Fax: (+33) 478 861 528. E-mail: jean-francois.nicolas@chu-lyon.fr

accepté le 15 Avril 2004

Haptens - contact allergens

Haptens often derive from unstable chemicals, named prohaptens, which require an additional metabolization step in vivo in the epidermis to be converted into an electrophilic hapten endowed with antigenic properties. This is the case of urushiol (poison ivy) [7] and of photosensitizers, which must be activated by UV-light in order to bind to epidermal proteins. Metal salts do not bind covalently to cutaneous proteins but form complexes with these proteins through weak interactions. Some metal salts also undergo chemical conversions in the skin, such as hexavalent chromium salts, which are turned into trivalent chromium, a highly reactive form binding to cutaneous proteins [8]. Evidence that the conversion of the parent compound into a reactive metabolite is necessary for the development of CS was recently demonstrated for the polyaromatic hydrocarbon (PAH) dimethylbenz(a)anthracene (DMBA). CS to DMBA only occurred in strains of mice that could metabolize the compound and inhibitors of PAH metabolism reduced the magnitude of the reaction. Furthermore, among the PAHs, only those that could induce aryl hydrocarbon hydroxylase, the rate-limiting enzyme in the PAH metabolic pathway, were immunogenic [9]. The implications of these experiments are that at least for some contact allergens, the metabolic status of the host is a key determinant of individual susceptibility to the development of allergic contact dermatitis.

Recent studies from several laboratories have shown that T cells recognize haptens as structural entities bound covalently to, or by complexation to, peptides anchored in the grooves of major histocompatibility (MHC) class I and class II molecules. Thus the contact allergen is a chemical but the antigen able to activate hapten-specific T cells is a haptenated peptide [10].

Pathophysiology of contact sensitivity

Phase 1 - Sensitization phase (also referred to as afferent phase or induction phase of CS)

Haptens or haptenated proteins are loaded by cutaneous dendritic cells (DC) and are expressed as haptenated peptides in the groove of MHC class I and class II molecules at the cell surface. Hapten-bearing DC migrate from the skin to the regional LN where specific CD8+ and CD4+ T lymphocytes are primed in the para-cortical area. T cells proliferate and emigrate out of the LNs to the blood where they recirculate between the lymphoid organs and the skin. The sensitization step lasts 10 to 15 days in man, and 5 to 7 days in the mouse. This first step has no clinical consequence.

The theory of the first contact of a chemical being immunogenic for the host is true for the strong haptens but cannot be accepted for the vast majority of haptens responsible for ACD. Indeed, ACD to moderate or weak haptens almost never occurs after the first contact but may take years of permanent skin exposure to develop.

Phase 2 - Elicitation phase (also known as efferent or challenge phase of CS)

The efferent phase of CS takes 72 hours in man, and 24 to 48 hours in the mouse. The inflammatory reaction persists only for a few days and rapidly decreases following down-regulatory mechanisms.

Primary allergic contact sensitivity

The central role of cutaneous dendritic cells

The basic role of epidermal Langerhans cells (LC) has been shown by two sets of experiments. On the one hand, animals painted with a hapten on cutaneous sites naturally or artificially depleted in LC are unable to mount a CS response [13, 14]. On the other hand, sensitization of naive mice can be achieved by injection of in vitro haptenized total epidermal cells, purified LC or FSDC dendritic cell lines, whereas injection of total epidermal cells depleted in LC before haptenization is inefficient in inducing sensitization [15-17].

Dermal DC could also participate in the induction phase of CS, even though their precise contribution and phenotype is not well known [18]. Recent studies by Geissmann et al have brought some insights into the turnover of macrophages and DC in the dermis in normal and inflammatory skin. Two different subsets of monocytes can be defined according to the expression of the chemokine receptor CCR2 [19, 20]. CCR2- monocytes appear to be involved in the physiological turnover of resident macrophages and DC, whereas CCR2+ monocytes are recruited in inflammatory sites where they could differentiate into mature DC able to present exogenous antigens to T cells. Since hapten application is responsible for activation of skin innate immunity, it is possible that the CCR2+ inflammatory monocytes which are recruited in the skin could uptake the hapten and participate in the afferent phase of CHS [21].

Cutaneous DC load haptens in the skin and migrate to the draining LN

Cutaneous DC continuously migrate out of the skin at a low rate which dramatically increases after hapten exposure [25]. This phenomenon is the consequence of numerous factors including the secretion of inflammatory cytokines and chemokines induced by the pro-inflammatory properties of the hapten itself. Fifteen minutes after hapten painting, LC start to synthesize IL-1β mRNA and to release the protein. Then, keratinocytes are activated and release TFN-α and GM-CSF [26]. In the epidermis, LC and keratinocytes are firmly associated by E-cadherine/E-cadherine junctions [27]. Binding of TNF-α and IL-1β on their cognate receptors (TNF-α RII and IL-1 RI and RII) expressed on LC, is followed by a decreased expression of E-cadherine on the LC membrane, allowing their disentanglement from surrounding keratinocytes [28–31]. Furthermore, IL-1β and TFN-α inhibit the expression of chemokine receptors such as CCR1, CCR2, CCR5 and CCR6 on the LC membrane, inducing a loss of sensitivity to their cognate ligands, in particular to MIP-3α (CCL20), a chemokine produced by keratinocytes [32]. In parallel, TNF-α and IL-1β induce the expression of adhesive molecules such as CD54, α6 integrin and different isoforms of CD44, which permit some interactions between LC and the extracellular matrix, allowing the migration of cutaneous DC.

In order to reach the lymphatic vessels, LC have to cross the dermo-epidermal junction and the dermis. To this end, LC secrete different types of enzymes, such as metalloproteinase (MMP) 3 and 9 [33], which could cleave macromolecules of the dermo-epidermal junction and of the extracellular matrix. They are also involved in the cleavage of E-cadherin and of pro-TNF-α in its biologically active form [34]. Once in the dermis, DC acquire sensitivity to the chemokines MIP-3β (CCL19) and SLC (CCL21) through the up-regulation of the chemokine receptor CCR7 [32, 35]. CCL21 is expressed on endothelial cells from lymphatic vessels and by stromal cells from the T cell area in LN [36]. The CCL21/CCR7 interaction is crucial during the sensitization phase of CS. Indeed, Endeman and colleagues have described a strong inhibition of CS following injections of SLC-blocking antibodies before and during the sensitization phase [37]. Moreover, TNF-α is able to induce a strong up-regulation of CCL21 on the endothelial cells of skin lymphatic vessels. The over-expression of CCL21 is of critical importance in the migratory properties of peripheral DC and is able to increase, by a factor of 10, the number of cutaneous DC able to migrate from the skin to the LN and subsequently the magnitude of antigen-specific T cell activation [38].

Maturation of cutaneous DC

DC maturation is also associated to the loss of capability to internalize and process exogenous antigens. Indeed, the expression of DC receptors such as mannose receptors or FcR receptors decreases during DC maturation. Birbeck granules disappear from LC and the intracellular machinery which controls macropinocytosis and phagocytosis is blocked [42]. Although this process was clearly demonstrated in vitro, recent in vivo data suggest, however, that mature migratory skin DC recovered from LN may still be able, at least for a proportion of them, to internalize, process and present some exogenous antigen [43].

In parallel, during the maturation process, DC express costimulatory molecules such as CD80 (B7-1), CD86 (B7-2), CD40, CD83, adhesive molecules such as CD54 (ICAM-1) and CD58 (LFA-3) and chemokine receptors such as CCR4, CCR7 and CXCR4, which permit them to migrate through lymphatic vessels .

In summary, cutaneous DCs uptake haptens in the skin and migrate to draining LNs. This migration is associated with an up-regulation of MHC and costimulatory molecules that confer a high efficiency in the priming of naive T cells to skin DC.

Hapten-specific T lymphocytes

Hapten specific T cell activation

T cell activation requires the combination of two distinct signals. The first signal involves the interaction of TCR and the MHC/peptide complex. The second signal requires costimulatory molecules and/or the secretion of cytokines and chemokines by DC. The absence of this second signal may lead to anergy or the death of the T cell which has already engaged its TCR.

Hapten determinants for T cells provide the first signal

The special nature of haptens may explain the different routes of processing that they could follow in antigen-presenting cells. Haptens could bind to extracellular and cell surface proteins which are internalized and processed into peptides via the endosomal/lysosomal compartments where they bind to the MHC class II groove. These haptenated peptides can eventually be recognized by class II-restricted CD4+ T cells. In addition, since most haptens are lipid soluble molecules they may also enter the cell, conjugate with intracytoplasmic proteins, and after processing in the endogenous route may be presented to MHC class I-restricted CD8+ T cells. Alternatively, direct binding of haptens, without processing, to a peptide in the groove of either MHC class I or class II molecules may also contribute to recognition by CD8+ or CD4+ T cells, respectively [50]. These different routes of hapten presentation have been demonstrated for the haptens TNP [51], urushiol [52] and arsonate [53]. These data point to the existence of both hapten-specific class I-restricted CD8+ T cells and class II-restricted CD4+ T cells.

The second signal is provided by mature DC

TCR engagement induces the activation of the nuclear factor NF-AT which regulates the IL-2 gene transcription. The instability of the IL-2 mRNA limits the production of this cytokine, which is essential for the proliferation and activation of T cells. One of the effects of CD28 engagement is to stabilize the IL-2 mRNA, leading to a 20 to 30 fold increase in IL-2 production [58]. Moreover through the activation of AP-1 and NF-kB, CD28 engagement induces an increase in IL-2 and anti apoptotic Bcl-XL gene transcription, which both protect T cells from the apoptotic signals received after TCR engagement [59].

Circulating CD4+ and CD8+ T cells penetrate in the paracortical area of LNs through the post capillary high endothelial venules (HEV) in response to the chemokine DC-CK1, secreted by resident DC of this zone [60]. The rare specific T cell precursors are activated by presentation of haptenated peptides by skin derived DC and start a program of clonal expansion and differentiation. This process is initiated by physical contact between T cells and DCs which implicate cell membrane remodeling, allowing the engagement of TCR/MHC-peptide complexes and costimulatory molecules with their cognate ligands. This membrane juxtaposition, associated with transmission of the information, presents some analogy with the neural synapse and is called immune synapse.

The plasmic membrane of mature DC expresses a high level of adhesive molecules which are essential for T cell activation. It comprises integrins such as CD54 and CD58 and the lectin DC-SIGN. These molecules interact respectively with LFA-1 (CD11a/CD18), a β2 integrin, CD2 and ICAM-3/2 molecules which are expressed on T cells [61]. In seconds following the T/DC interaction, a small number of TCR engagements leads to cytoskeleton rearrangement by actine polymerisation, and activation of ZAP-70 and the adaptative protein Vav-1 [62]. These modifications generate a central zone, rich in MHC-peptide /TCR complex surrounded by an integrin ring called SMAC (for supramolecular activation cluster). In this zone, CD4+ and CD8+ molecules are progressively replaced by CD28 and CTLA-4 [63].

Other couplings of costimulatory molecules from the TNF-TNF family receptors such as CD40/CD40-L or RANK/RANK-L participate in T cell activation. Their interactions lead to the up-regulation of OX40-L on DC membranes. Interaction between OX40-L and OX40, expressed on activated T cells, induces an over expression of CD80 and CD86 and thus a better T cell activation which is of relevance for CS because mice deficient for OX40-L display a dramatic decrease in CS reaction to oxazolone, DNFB, and FITC. This poor CS response was due to deficient T cell priming, as shown by decreased T cell proliferation induced by DC from OX40-L deficient mice [64].

T cell polarization and constitution of CD4+ and CD8+ T cell populations

Depending on the pattern of cytokine secretion, different functional subpopulations of T lymphocytes serve to determine the qualitative aspects of the adaptative immune response. CD4+ Th1 cells produce IFN-γ, IL-2 and TNF-α, and CD4+ Th2 cells produce IL-4, IL-10, IL-13, and IL-5. Similarly, Tc1 cells produce type 1 cytokines (IFN-γ, IL-2 and TNF-α) and Tc2 cells type 2 cytokines (IL-4, IL-10, IL-13, and IL-5). However, Tc2 cells could also produce TNF-α in some conditions [65]. A simplification of the nomenclature is the use of “type 1” and “type 2” cytokine pattern for either CD4+ and CD8+ T cells.

For CD4+ and CD8+ T cells, orientation through one or the other subtype is dependent on comparable environmental factors [67]. In vitro treatment of APC/T cells mixtures with IL-4 plus anti-IFN-γ mAb polarizes T cells to a type 2 phenotype, whereas IL-12 plus anti-IL-4 mAb treatment polarizes T cells to a type 1 phenotype. However, the mechanisms implicated during the T cell-DC dialogue in vivo which are responsible for the polarization of T cells are still poorly understood.

Two hypotheses have been recently proposed to explain the basis of the dichotomy of T cell responses. The first hypothesis postulates the existence of distinct DC subpopulations (DC1 versus DC2) involved in the polarization of the immune response (type 1 versus type 2). After CD40 triggering, one subpopulation of DC, derived from monocytes in humans or expressing CD8α in mouse (myeloid), referred to as DC1, would provoke a type 1 response by producing high amounts of IL-12. The other subpopulation, derived from plasmacytoïd DC in human and CD8α neg in mouse (lymphoid) and defined as DC2, produces few IL–12 and might be able to induce a type 2 response [68]. However, CD8α neg cells can prime both type 1 and type 2 responses depending on the activation signal they received [69, 70], demonstrating that the phenotype of a given DC subset cannot be considered as a marker of functionality for the activation of type 1 versus type 2 T cells. The second hypothesis considers that environmental factors will influence the maturation process of a given DC enabling it to prime for type 1 or type 2 T cells [71]. Along this line, Soumelis et al have reported that human epithelial cells produce a cytokine, thymic stromal lymphopoietin (TSLP), that binds to specific receptors on CD11c+DCs [72]. This induces the production of Th2-attracting chemokines and primes naïve T cells for a Th2 phenotype.

Polarization of type 1 T cells is crucial to the development of specific effector T cell populations and optimal CS reaction. CS to DNFB is due to CD8+ effector type 1 T cells and is regulated by CD4+ type 2 T cells [73, 74]. Type 1 polarization by injection of IL-12 at the time of sensitization favors CD8+ T cell differentiation and increases the CS reaction [75]. On the contrary, type 2 polarization using IL-4 (or anti-IFNγ mAbs) leads to a diminished CS response associated with an altered CD8+ T cell priming [75].

Need for CD4+ help in hapten-specific CD8+ responses?

That CD4+ T cell help is not necessary for development of CHS is in keeping with recent studies showing that antigen-specific cytotoxic lymphocyte (CTL) responses can be induced in the absence of help provided that i) the immunogen has intrinsic proinflammatory properties (e.g. endotoxins and pathogenic microorganisms) able to generate a danger signal to the DC [83]; ii) the affinity of TCR for MHC/peptide complexes is high; iii) the frequency of specific CD8+ T cell precursors is high [85]. Contact sensitizing haptens have two important properties that may explain their immunogenicity in the absence of CD4+ help. First, they are proinflammatory xenobiotics through induction of chemokine and cytokine production by skin cells [3]. Second, covalent binding of haptens, such as DNFB or TNCB, on amino acid residues of proteins generates a high number of haptenated peptides allowing activation of high numbers of CTL precursors [85].

Migration of specific T cells in the blood and in the skin

CD4+ and CD8+ T cells found in the skin of sensitized mice, express CCR4, α4β1 integrin and cutaneous lymphocyte antigen (CLA) [87]. Skin-selective homing of primed T cells depends on tissue microenvironment and more specifically on skin dendritic cells [88]. Migration of T cells from the blood to the skin occurs at the site of post capillary HEV through interactions of CLA and CCR4 with their respective ligands, E-, P-selectine and TARC (CCL17), constitutively expressed on endothelial cells [89–92]. The passage of T cells in the dermis requires the sequential interaction of VLA-4 and LFA-1 receptors on T cells with VCAM-1 and ICAM-1 on endothelial cells [93].

Thus, at the end of the afferent phase of CHS, specific T cells which have been activated by hapten-bearing DC are found in the LNs (central memory cells), in the blood and in the skin (peripheral memory cells). The skin has a normal looking appearance. Specific T cells will be activated directly in the skin and massively recruited upon a subsequent skin contact with the same hapten.

Expression of contact sensitivity reaction

T cell recruitment

That CD8+ and CD4+ T cells are recruited at different times after hapten painting may be explained by the differential expression of chemokine receptors by T cell subsets as well as by the sequential production of chemokines during the development of the skin inflammation. Even if it is still unclear which chemokines drive the initial influx of T cells, the recruitment of activated CD8+ T cells seems to be under the control of the IP-10/CXCR3 chemokine/chemokine receptor pathway [97–99]. The contribution of IP-10 (CXCL10) has been recently suggested by a study showing that IP-10 deficient mice present a deficient skin recruitment in IFN-γ producing T cells and a diminished CS reaction [100]. The recruitment of CD4+ T cells is possibly under the control of the MDC (CCL22) and TARC (CCL17) chemokines and their receptor CCR4 expressed on activated CD4+ T cells [92]. These two chemokines are up regulated in the skin around 12 hours after hapten exposure concomitantly with the infiltration of mononuclear cells. Another recently described chemokine, CTACK (CCL27) and its receptor CCR10, is also important in the traffic of activated T cells in the skin [101, 102]. This chemokine is constitutively expressed by keratinocytes and its synthesis is up-regulated following IL-1β and TNF-α exposure.

In parallel to chemokines and chemokine receptors, adhesion molecules (CLA, VLA-4 and LFA-1) are involved in the infiltration of T cells in the skin. Under the influence of TNF-α, endothelial cells up-regulate their respective ligands (E-, P-selectine, VCAM-1 and ICAM-1) allowing a direct interaction with T cells and their extravasation in the dermis.

Characterization of effector T cells

Animals models have contributed to elucidate the nature of the effector T cell population in CS. Mice deficient in CD8+ T cells, following the invalidation of the MHC class I β2 microglobulin gene, or mice depleted in CD8+ T cells, are unable to develop a CS reaction to experimental haptens [73]. However, lack of CD8+ T cells in these mice does not affect the classical DTH to proteins. Alternatively, mice deficient in CD4+ T cells, following the invalidation of the MHC class II Aβ gene, or mice depleted in CD4+ T cells, develop a stronger and sustained CS reaction, suggesting a regulatory function for the CD4+ T cell compartment [73]. Thus CS appears as very different from classical DTH reactions in term of T cell subset involved in the effector pro-inflammatory functions. Recent studies on nickel ACD have confirmed that the pathophysiology of ACD in humans was similar to that of CS in mice and involved CD8+ effector T cells and CD4+ regulatory T cells [106].

IFN-γ production by CD8+ T cells

TCR engagement induces the release of type 1 cytokines such as IFN-γ, which in turn is responsible for the increased production in the skin of IP-10, IP-9 and Mig, of IL-1, IL-6, TFN-α, GM-CSF and MIP-2 (CXCL8). This complex cytokine and chemokine production amplifies the inflammatory response initiated by the hapten (IL-1, TNF-α) and is responsible for the massive infiltration of leukocytes. Recruited cells comprise polynuclear neutrophils, T cells and inflammatory monocytes able to differentiate into macrophages and dendritic cells.

Resident mast cells have been recently proposed to be key regulators of the amplification phase of the skin inflammation [107]. Indeed, following CD8+ T cell activation, mast cells produce TNF-α and MIP-2 which are both needed for the recruitment of neutrophils constitutively expressing CXCR1 and 2.

Cytotoxic activity of CD8+ T cells

Keratinocytes are the main targets of the cytotoxic effect of hapten specific CD8+ T cells [110]. Keratinocyte apoptosis coincides with CD8+ T cell arrival in the epidermis and increases proportionally with the number of infiltrating CD8+ T cells [96]. These epidermal damages facilitate the penetration of haptens present on the skin which may increase the inflammation [111]. Finally, perforin release by CD8+ T cells is associated to the production of RANTES, MIP-1α and MIP-1β, which mediate the recruitment of CCR1+ and CCR5+ monocytes and granulocytes [112].

In summary, hapten-specific type 1 T cell activation leads to the production of a cascade of cytokines and chemokines by skin cells which induce a massive recruitment of leukocytes responsible for the cutaneous changes typical of CS. After a peak obtained at 24/48 hours, the inflammation starts to resolve slowly by active down-regulatory mechanisms which limit the tissular damages and maintain the skin integrity.

Regulation of contact sensitivity

The regulation of CS could be divided into two phases, a central and peripheral phase [115, 116]. The central regulatory phase controls the expansion and differentiation of CD8+ effector T cells in the LNs while the peripheral phase limits the inflammatory process generated in the skin. CD4+CD25+ natural regulatory T cells seem to be involved in the first phase. Indeed, a recent study has shown that CD4+CD25+ T cells are necessary in the oral tolerance phenomenon to haptens through the total inhibition of the clonal expansion of hapten-specific CD8+ T cells [114, 117]. Moreover, mice treated with an IL-2-IgG2b fusion protein, showed a decreased CS reaction associated with an increase in the CD4+CD25+ T cell subset [118]. Finally, depletion of CD4+25+ T cells by in vivo treatment of mice with an anti-CD25 mAb at the time of sensitization led to an enhanced CS reaction and an increased CD8+ T cell priming (Dubois B and Kaiserlian D, unpublished data).

The mechanisms by which CD4+ T cells (CD4+25+ and/or CD4+25- T cells) limit the skin inflammatory reaction are still not understood and may involve IL-10 and other immunosuppressive cytokines [106]. The immunosuppressive effect occurs through the inhibition of production of IFN-γ, IL-6, IL-1, GM-CSF and TNF-α. IL-10 plays a crucial role in the down-regulation of CS reactions inasmuch as IL-10-deficient mice mount an exaggerated CS reaction to oxazolone, increased in both magnitude and duration as compared to wild type mice. Moreover, IL-10 injection before challenge totally abrogated the CS response [119]. Finally, resolution of CS is associated with the recruitment in the skin of a regulatory CCR8+ T cell population which produces a large amount of IL-10 around 24 hours post-challenge [120]. The production of IL-10 is not restricted to T cells and can be supplied locally by other cells such as keratinocytes which synthesize the cytokine by 48/72 hours after hapten painting [121].

Other regulatory mechanisms may be involved in the resolution of CS. As an example, in the presence of a large quantity of IFN-γ, endothelial cells down-regulate the expression of E and P selectins, thereby limiting the arrival of new infiltrating leucocytes in the dermis [122].

Clinical hallmarks

Histopathology of allergic contact dermatitis

Diagnosis

Patch testing is the universally accepted method for the detection of the causative contact allergens. The positive patch test reproduces an experimental contact dermatitis on a limited area of the skin. A good patch test indicates contact sensitization of past or present relevance and produces no false-positive reaction. Based on the principles of evidence-based medicine, patch testing is cost-effective only if patients are selected on the basis of a clear-cut clinical suspicion of contact allergy and only if patients are tested with chemicals relevant to the problem [124]. Finn chambers and several other tape methods are currently in use [125]. Most allergens used in patch testing are well-defined chemical substances. To save place and time, mixes of chemically related chemicals may be used. The most frequently encountered contact allergens have been selected by various international contact dermatitis groups and included in standard patch test series [126]. There are additional series aimed towards specific occupations and other spheres of activities. Most commercially available allergens supplied in syringes are incorporated in petrolatum. Considerable efforts have been made to standardize the concentration of the allergens to ensure comparable results worldwide. Great care must be taken in testing with non standardized chemicals not found in commercially available kits because testing with irritant concentrations may result in false positive reactions [127].

Patch tests are usually applied for 48 hours on the upper half of the back. Patches are read at least 20 minutes after their removal.

The method of recording recommended by the European and North American contact dermatitis groups is as follows [128]:

• + weak positive reaction: erythema, infiltration, possibly papules
• ++ strong positive reaction: erythema, infiltration, papules, vesicles
• +++ extreme positive reaction: intense erythema and infiltration, coalescing vesicles, bullous reaction.
• ? doubtful reaction (weak erythema only)
• IR irritant reaction of different types
• NR negative reaction
• NT not tested

It is recommended to perform a second reading 24 or 48 hours after patch test removal. In doing only a single reading, a large number of delayed reactions will be missed, while others due to early irritant effects will be considered as allergic [127]. The type of positive reaction that can safely be interpreted as indicating allergic contact sensitivity exhibits erythema, edema, and small vesicles extending slightly beyond the patch border. Pruritus and reactivation of previous eczematous skin lesions at the time of testing indicate allergy.

When a positive patch test is considered to reveal a genuine contact sensitivity, a decision has to be taken as to its relevance. Current relevance is related to “current clinical symptoms, occurring in the last few days or weeks”; past relevance refers to older clinical events [129]. The major prerequisites for a contact allergy to be clinically relevant are: i) exposure to the sensitizer; ii) presence of a dermatitis which is understandable and explainable with regard to the exposure, on the one hand, and type, localization and course of the dermatitis, on the other hand [130].

Common causes of allergic contact dermatitis

Metals

Chromate is the most common contact allergen in men and sensitization to it is usually occupational. Occupational exposure is most frequent in construction workers who handle cement. Other common sources are chrome-tanned leather, bleaching agents, paints, and printing solutions.

Cosmetics and skin care products

Dermatitis from clothes and shoes

Drug dermatitis

Plant dermatitis

Treatment

Topical steroids are used in the acute stage and are gradually replaced by ointments and cold creams as the skin lesions withdraw. If ACD is widespread and severe, systemic corticosteroids may be indicated for a short period of time.

Reducing the total body load of nickel has been attempted in nickel eczema by means of a nickel-restricted diet and by treatment with disulfiram. Trials have yielded conflicting results as regards the clinical effect of the treatment and the application of the metal-chelator disulfiram was limited by serious side effects [139].

Oral hyposensitization to urushiol and nickel has been attempted but is not performed in practice.

Conventional immunosuppressive therapy is not appropriate in the management of ACD. New immunomodulating macrolactams have been successfully tested in clinical trials [140–142]. Perspectives in pharmacological intervention include new classes of immunosuppressors, inhibitors of cellular metabolic activity, inhibitors of cell adhesion molecules, targetted skin application of regulatory cytokines and neutralization of pro-inflammatory cytokines (antisense oligonucleoides, anticytokine antibodies, soluble cytokine receptors).

Conclusion

Acknowledgments

References

2 Krasteva , et-al. Contact dermatitis II. Clinical aspects and diagnosis Eur J Dermatol 9 1999 144-159

3 Krasteva , et-al. Contact dermatitis I. Pathophysiology of contact sensitivity Eur J Dermatol 9 1999 65-77

4 Lepoittevin , Leblond Hapten-peptide T cell receptor interactions: molecular basis for the recognition of haptens by T lymphocytes Eur J Dermatol 7 1997 151-154

5 Dupuis Nature of hapten-protein interactions. Chemically reactive function in haptens and proteins, in allergic contact dermatitis to simple chemicals. A molecular approach Calnan , Maibach 1982 Ed Marcel Dekker, Inc.: New-York

6 Berard , Marty , Nicolas Allergen penetration through the skin Eur J Dermatol 13 2003 324-330

7 Dupuis Studies on poison ivy. In vitro lymphocyte transformation by urushiol-protein conjugates Br J Dermatol 101 1979 617-624

8 Saloga , Knop , Kolde Ultrastructural cytochemical visualization of chromium in the skin of sensitized guinea pigs Arch Dermatol Res 280 1988 214-219

9 Anderson , et-al. Metabolic requirements for induction of contact hypersensitivity to immunotoxic polyaromatic hydrocarbons J Immunol 155 1995 3530-3537

10 Martin , Ortmann , Pflugfelder , Birsner , Weltzien Role of hapten-anchoring peptides in defining hapten-epitopes for MHC-restricted cytotoxic T cells. Cross-reactive TNP-determinants on different peptides J Immunol 149 1992 2569-2575

11 Vigan , Girardin , Adessi , Laurent Late reading of patch tests Eur J Dermatol 7 1997 574-576

12 Saint-Mezard , et-al. Afferent and efferent phases of allergic contact dermatitis (ACD) can be induced after a single skin contact with haptens: evidence using a mouse model of primary ACD J Invest Dermatol 120 2003 641-647

13 Toews , Bergstresser , Streilein Epidermal Langerhans cell density determines whether contact hypersensitivity or unresponsiveness follows skin painting with DNFB J Immunol 124 1980 445-453

14 Lynch , Gurish , Daynes Relationship between epidermal Langerhans cell density ATPase activity and the induction of contact hypersensitivity J Immunol 126 1981 1892-1897

15 Ptak , Rozycka , Askenase , Gershon Role of antigen-presenting cells in the development and persistence of contact hypersensitivity J Exp Med 151 1980 362-375

16 Tamaki , Fujiwara , Levy , Shearer , Katz Hapten specific TNP-reactive cytotoxic effector cells using epidermal cells as targets J Invest Dermatol 77 1981 225-229

17 Girolomoni , et-al. Establishment of a cell line with features of early dendritic cell precursors from fetal mouse skin Eur J Immunol 25 1995 2163-2169

18 Caux Pathways of development of human dendritic cells Eur J Dermatol 8 1998 375-384

19 Kurimoto , Grammer , Shimizu , Nakamura , Streilein Role of F4/80+ cells during induction of hapten-specific contact hypersensitivity Immunology 85 1995 621-629

20 Geissmann , Jung , Littman Blood monocytes consist of two principal subsets with distinct migratory properties Immunity 19 2003 71-82

21 Taylor , Gordon Monocyte heterogeneity and innate immunity Immunity 19 2003 2-4

22 Frey , Wenk Experimental studies on the pathogenesis of contact eczema in the guinea-pig Int Arch Allergy Appl Immunol 11 1957 81-100

23 Macatonia , Edwards , Knight Dendritic cells and the initiation of contact sensitivity to fluorescein isothiocyanate Immunology 59 1986 509-514

24 Macatonia , Knight , Edwards , Griffiths , Fryer Localization of antigen on lymph node dendritic cells after exposure to the contact sensitizer fluorescein isothiocyanate. Functional and morphological studies J Exp Med 166 1987 1654-1667

25 Kamath , Henri , Battye , Tough , Shortman Developmental kinetics and lifespan of dendritic cells in mouse lymphoid organs Blood 100 2002 1734-1741

26 Enk , Angeloni , Udey , Katz An essential role for Langerhans cell-derived IL-1 beta in the initiation of primary immune responses in skin J Immunol 150 1993 3698-3704

27 Borkowski , et-al. Expression of E-cadherin by murine dendritic cells: E-cadherin as a dendritic cell differentiation antigen characteristic of epidermal Langerhans cells and related cells Eur J Immunol 24 1994 2767-2774

28 Schwarzenberger , Udey Contact allergens and epidermal proinflammatory cytokines modulate Langerhans cell E-cadherin expression in situ J Invest Dermatol 106 1996 553-558

29 Wang , et-al. Tumour necrosis factor receptor II (p75) signalling is required for the migration of Langerhans’ cells Immunology 88 1996 284-288

30 Wang , et-al. Depressed Langerhans cell migration and reduced contact hypersensitivity response in mice lacking TNF receptor p75 J Immunol 159 1997 6148-6155

31 Tang , Amagai , Granger , Stanley , Udey Adhesion of epidermal Langerhans cells to keratinocytes mediated by E-cadherin Nature 361 1993 82-85

32 Dieu , et-al. Selective recruitment of immature and mature dendritic cells by distinct chemokines expressed in different anatomic sites J Exp Med 188 1998 373-386

33 Kobayashi , Matsumoto , Kotani , Makino Possible involvement of matrix metalloproteinase-9 in Langerhans cell migration and maturation J Immunol 163 1999 5989-5993

34 Gearing , et-al. Processing of tumour necrosis factor-alpha precursor by metalloproteinases Nature 370 1994 555-557

35 Cyster Chemokines and the homing of dendritic cells to the T cell areas of lymphoid organs J Exp Med 189 1999 447-450

36 Ngo , et-al. Lymphotoxin alpha/beta and tumor necrosis factor are required for stromal cell expression of homing chemokines in B and T cell areas of the spleen J Exp Med 189 1999 403-412

37 Engeman , Gorbachev , Gladue , Heeger , Fairchild Inhibition of functional T cell priming and contact hypersensitivity responses by treatment with anti-secondary lymphoid chemokine antibody during hapten sensitization J Immunol 164 2000 5207-5214

38 Martin-Fontecha , et-al. Regulation of dendritic cell migration to the draining lymph node: impact on T lymphocyte traffic and priming J Exp Med 198 2003 615-621

39 Becker , Neiss , Neis , Reske , Knop Contact allergens modulate the expression of MHC class II molecules on murine epidermal Langerhans cells by endocytotic mechanisms J Invest Dermatol 98 1992 700-705

40 Becker , Mohamadzadeh , Reske , Knop Increased level of intracellular MHC class II molecules in murine Langerhans cells following in vivo and in vitro administration of contact allergens J Invest Dermatol 99 1992 545-549

41 Pierre , Mellman Developmental regulation of invariant chain proteolysis controls MHC class II trafficking in mouse dendritic cells Cell 93 1998 1135-1145

42 Garrett , et-al. Developmental control of endocytosis in dendritic cells by Cdc42 Cell 102 2000 325-334

43 Ruedl , Koebel , Karjalainen In vivo-matured Langerhans cells continue to take up and process native proteins unlike in vitro-matured counterparts J Immunol 166 2001 7178-7182

44 Waksman Cellular hypersensitivity immunity : inflammation and cytotoxicity Parkers 1978 Saunders, Philadelphia 173-218

45 Weltzien , et-al. T cell immune responses to haptens. Structural models for allergic and autoimmune reactions Toxicology 107 1996 141-151

46 von Bonin , Ortmann , Martin , Weltzien Peptide-conjugated hapten groups are the major antigenic determinants for trinitrophenyl-specific cytotoxic T cells Int Immunol 4 1992 869-874

47 Kohler , Hartmann , Grimm , Pflugfelder , Weltzien Carrier-independent hapten recognition and promiscuous MHC restriction by CD4+ T cells induced by trinitrophenylated peptides J Immunol 158 1997 591-597

48 Cavani , Hackett , Wilson , Rothbard , Katz Characterization of epitopes recognized by hapten-specific CD4+ T cells J Immunol 154 1995 1232-1238

49 Gamerdinger , et-al. A new type of metal recognition by human T cells: contact residues for peptide-independent bridging of T cell receptor and major histocompatibility complex by nickel J Exp Med 197 2003 1345-1353

50 Sinigaglia The molecular basis of metal recognition by T cells J Invest Dermatol 102 1994 398-401

51 Martin , von Bonin , Fessler , Pflugfelder , Weltzien Structural complexity of antigenic determinants for class I MHC-restricted, hapten-specific T cells. Two qualitatively differing types of H-2Kb-restricted TNP epitopes J Immunol 151 1993 678-687

52 Kalish , Wood , LaPorte Processing of urushiol (poison ivy) hapten by both endogenous and exogenous pathways for presentation to T cells in vitro J Clin Invest 93 1994 2039-2047

53 Nalefski , Rao Nature of the ligand recognized by a hapten- and carrier-specific, MHC-restricted T cell receptor J Immunol 150 1993 3806-3816

54 Reiser , Schneeberger Expression and function of B7-1 and B7-2 in hapten-induced contact sensitivity Eur J Immunol 26 1996 880-885

55 Symington , Brady , Linsley Expression and function of B7 on human epidermal Langerhans cells J Immunol 150 1993 1286-1295

56 Kondo , Kooshesh , Wang , Fujisawa , Sauder Contribution of the CD28 molecule to allergic and irritant-induced skin reactions in CD28 -/- mice J Immunol 157 1996 4822-4829

57 Xu , Heeger , Fairchild Distinct roles for B7-1 and B7-2 determinants during priming of effector CD8+ Tc1 and regulatory CD4+ Th2 cells for contact hypersensitivity J Immunol 159 1997 4217-4226

58 Fraser , Irving , Crabtree , Weiss Regulation of interleukin-2 gene enhancer activity by the T cell accessory molecule CD28 Science 251 1991 313-316

59 Boise , et-al. CD28 costimulation can promote T cell survival by enhancing the expression of Bcl-XL Immunity 3 1995 87-98

60 Adema , et-al. A dendritic-cell-derived C-C chemokine that preferentially attracts naive T cells Nature 387 1997 713-717

61 Geijtenbeek , et-al. Identification of DC-SIGN, a novel dendritic cell-specific ICAM-3 receptor that supports primary immune responses Cell 100 2000 575-585

62 Krawczyk , et-al. Vav1 controls integrin clustering and MHC/peptide-specific cell adhesion to antigen-presenting cells Immunity 16 2002 331-343

63 Monks , Freiberg , Kupfer , Sciaky , Kupfer Three-dimensional segregation of supramolecular activation clusters in T cells Nature 395 1998 82-86

64 Chen , et-al. Ox40-ligand has a critical costimulatory role in dendritic cell:T cell interactions Immunity 11 1999 689-698

65 Sad , Marcotte , Mosmann Cytokine-induced differentiation of precursor mouse CD8+ T cells into cytotoxic CD8+ T cells secreting Th1 or Th2 cytokines Immunity 2 1995 271-279

66 Hahn , et-al. Down-modulation of CD4+ T helper type 2 and type 0 cells by T helper type 1 cells via Fas/Fas-ligand interaction Eur J Immunol 25 1995 2679-2685

67 Li , Sad , Kagi , Mosmann CD8+Tc1 and Tc2 cells secrete distinct cytokine patterns in vitro and in vivo but induce similar inflammatory reactions J Immunol 158 1997 4152-4161

68 Maldonado-Lopez , Maliszewski , Urbain , Moser Cytokines regulate the capacity of CD8+alpha(+) and CD8+alpha(-) dendritic cells to prime Th1/Th2 cells in vivo J Immunol 167 2001 4345-4350

69 Cella , Facchetti , Lanzavecchia , Colonna Plasmacytoid dendritic cells activated by influenza virus and CD4+0L drive a potent TH1 polarization Nat Immunol 1 2000 305-310

70 MacDonald , Straw , Bauman , Pearce CD8+- dendritic cell activation status plays an integral role in influencing Th2 response development J Immunol 167 2001 1982-1988

71 Ardavin , et-al. Origin and differentiation of dendritic cells Trends Immunol 22 2001 691-700

72 Soumelis , et-al. Human epithelial cells trigger dendritic cell mediated allergic inflammation by producing TSLP Nat Immunol 3 2002 673-680

73 Bour , et-al. Major histocompatibility complex class I-restricted CD8+ T cells and class II-restricted CD4+ T cells, respectively, mediate and regulate contact sensitivity to dinitrofluorobenzene Eur J Immunol 25 1995 3006-3010

74 Xu , DiIulio , Fairchild T cell populations primed by hapten sensitization in contact sensitivity are distinguished by polarized patterns of cytokine production: interferon gamma-producing (Tc1) effector CD8+ T cells and interleukin (Il) 4/Il-10-producing (Th2) negative regulatory CD4+ T cells J Exp Med 183 1996 1001-1012

75 Gorbachev , DiIulio , Fairchild IL-12 augments CD8+ T cell development for contact hypersensitivity responses and circumvents anti-CD154 antibody-mediated inhibition J Immunol 167 2001 156-162

76 Gocinski , Tigelaar Roles of CD4+ and CD8+ T cells in murine contact sensitivity revealed by in vivo monoclonal antibody depletion J Immunol 144 1990 4121-4128

77 Bouloc , Cavani , Katz Contact hypersensitivity in MHC class II-deficient mice depends on CD8+ T lymphocytes primed by immunostimulating Langerhans cells J Invest Dermatol 111 1998 44-49

78 Kolesaric , Stingl , Elbe-Burger MHC class I+/II- dendritic cells induce hapten-specific immune responses in vitro and in vivo J Invest Dermatol 109 1997 580-585

79 Krasteva , et-al. Dual role of dendritic cells in the induction and down-regulation of antigen-specific cutaneous inflammation J Immunol 160 1998 1181-1190

80 Martin , et-al. Peptide immunization indicates that CD8+ T cells are the dominant effector cells in trinitrophenyl-specific contact hypersensitivity J Invest Dermatol 115 2000 260-266

81 Xu , DiIulio , Fairchild T cell populations primed by hapten sensitization in contact sensitivity are distinguished by polarized patterns of cytokine production: interferon gamma-producing (Tc1) effector CD8+ T cells and interleukin (Il) 4/Il-10-producing (Th2) negative regulatory CD4+ T cells J Exp Med 183 1996 1001-1012

82 Xu , Banerjee , Dilulio , Fairchild Development of effector CD8+ T cells in contact hypersensitivity occurs independently of CD4+ T cells J Immunol 158 1997 4721-4728

83 Matzinger The danger model: a renewed sense of self Science 296 2002 301-305

84 Wang , et-al. Multiple paths for activation of naive CD8+ T cells: CD4+-independent help J Immunol 167 2001 1283-1289

85 Martin , et-al. A high frequency of allergen-specific CD8+ Tc1 cells is associated with the murine immune response to the contact sensitizer trinitrophenyl Exp Dermatol 12 2003 78-85

86 Sallusto , Lenig , Forster , Lipp , Lanzavecchia Two subsets of memory T lymphocytes with distinct homing potentials and effector functions Nature 401 1999 708-712

87 Santamaria-Babi CLA+ T cells in cutaneous diseases Eur J Dermatol 14 2004 13-18

88 Dudda , Simon , Martin Dendritic cell immunization route determines CD8+ T cell trafficking to inflamed skin: role for tissue microenvironment and dendritic cells in establishment of T cell-homing subsets J Immunol 172 2004 857-863

89 Berg , et-al. The cutaneous lymphocyte antigen is a skin lymphocyte homing receptor for the vascular lectin endothelial cell-leukocyte adhesion molecule 1 J Exp Med 174 1991 1461-1466

90 Campbell , et-al. The chemokine receptor CCR4 in vascular recognition by cutaneous but not intestinal memory T cells Nature 400 1999 776-780

91 Erdmann , et-al. Fucosyltransferase VII-deficient mice with defective E-, P-, and L-selectin ligands show impaired CD4+ and CD8+ T cell migration into the skin, but normal extravasation into visceral organs J Immunol 168 2002 2139-2146

92 Reiss , Proudfoot , Power , Campbell , Butcher CC chemokine receptor (CCR)4 and the CCR10 ligand cutaneous T cell-attracting chemokine (CTACK) in lymphocyte trafficking to inflamed skin J Exp Med 194 2001 1541-1547

93 Santamaria , Perez Soler , Hauser , Blaser Allergen specificity and endothelial transmigration of T cells in allergic contact dermatitis and atopic dermatitis are associated with the cutaneous lymphocyte antigen Int Arch Allergy Immunol 107 1995 359-362

94 Enk , Katz Early molecular events in the induction phase of contact sensitivity Proc Natl Acad Sci U S A 89 1992 1398-1402

95 Heufler , et-al. Cytokine gene expression in murine epidermal cell suspensions: interleukin 1 beta and macrophage inflammatory protein 1 alpha are selectively expressed in Langerhans cells but are differentially regulated in culture J Exp Med 176 1992 1221-1226

96 Akiba , et-al. Skin inflammation during contact hypersensitivity is mediated by early recruitment of CD8+ T cytotoxic 1 cells inducing keratinocyte apoptosis J Immunol 168 2002 3079-3087

97 Albanesi , et-al. A cytokine-to-chemokine axis between T lymphocytes and keratinocytes can favor Th1 cell accumulation in chronic inflammatory skin diseases J Leukoc Biol 70 2001 617-623

98 Bonecchi , et-al. Differential expression of chemokine receptors and chemotactic responsiveness of type 1 T helper cells (Th1s) and Th2s J Exp Med 187 1998 129-134

99 Flier , et-al. The CXCR3 activating chemokines IP-10, Mig, and IP-9 are expressed in allergic but not in irritant patch test reactions J Invest Dermatol 113 1999 574-578

100 Dufour , et-al. IFN-gamma-inducible protein 10 (IP-10; CXCL10)-deficient mice reveal a role for IP-10 in effector T cell generation and trafficking J Immunol 168 2002 3195-3204

101 Homey , et-al. Cutting edge: the orphan chemokine receptor G protein-coupled receptor-2 (GPR-2, CCR10) binds the skin-associated chemokine CCL27 (CTACK/ALP/ILC) J Immunol 164 2000 3465-3470

102 Homey , et-al. CCL27-CCR10 interactions regulate T cell-mediated skin inflammation Nat Med 8 2002 157-165

103 Cher , Mosmann Two types of murine helper T cell clone. II. Delayed-type hypersensitivity is mediated by TH1 clones J Immunol 138 1987 3688-3694

104 Gawkrodger , Vestey , Wong , Buxton Contact clinic survey of nickel-sensitive subjects Contact Dermatitis 14 1986 165-169

105 Silvennoinen-Kassinen , Ikaheimo , Karvonen , Kauppinen , Kallioinen Mononuclear cell subsets in the nickel-allergic reaction in vitro and in vivo J Allergy Clin Immunol 89 1992 794-800

106 Cavani , Albanesi , Traidl , Sebastiani , Girolomoni Effector and regulatory T cells in allergic contact dermatitis Trends Immunol 22 2001 118-120

107 Biedermann , et-al. Mast cells control neutrophil recruitment during T cell-mediated delayed-type hypersensitivity reactions through tumor necrosis factor and macrophage inflammatory protein 2 J Exp Med 192 2000 1441-1452

108 Saulnier , Huang , Aguet , Ryffel Role of interferon-gamma in contact hypersensitivity assessed in interferon-gamma receptor-deficient mice Toxicology 102 1995 301-312

109 Kehren , et-al. Cytotoxicity is mandatory for CD8+(+) T cell-mediated contact hypersensitivity J Exp Med 189 1999 779-786

110 Traidl , et-al. Disparate cytotoxic activity of nickel-specific CD8+ and CD4+ T cell subsets against keratinocytes J Immunol 165 2000 3058-3064

111 Trautmann , Akdis , Brocker , Blaser , Akdis New insights into the role of T cells in atopic dermatitis and allergic contact dermatitis Trends Immunol 22 2001 530-532

112 Wagner , et-al. Beta-chemokines are released from HIV-1-specific cytolytic T-cell granules complexed to proteoglycans Nature 391 1998 908-911

113 Gorbachev , Fairchild CD4+(+) T Cells Regulate CD8+(+) T Cell-Mediated Cutaneous Immune Responses by Restricting Effector T Cell Development through a Fas Ligand-Dependent Mechanism J Immunol 172 2004 2286-2295

114 Dubois , Chapat , Goubier , Kaiserlian CD4+CD25+ T cells as key regulators of immune responses Eur J Dermatol 13 2003 111-116

115 Gorbachev , Fairchild Regulatory role of CD4+ T cells during the development of contact hypersensitivity responses Immunol Res 24 2001 69-77

116 Gorbachev , Fairchild Induction and regulation of T-cell priming for contact hypersensitivity Crit Rev Immunol 21 2001 451-472

117 Dubois , et-al. Innate CD4+CD25+ regulatory T cells are required for oral tolerance and control CD8+ T cells mediating skin inflammation Blood 102 2003 3295-3330

118 Ruckert , Brandt , Hofmann , Bulfone-Paus , Paus IL-2-IgG2b fusion protein suppresses murine contact hypersensitivity in vivo J Invest Dermatol 119 2002 370-376

119 Ferguson , Dube , Griffith Regulation of contact hypersensitivity by interleukin 10 J Exp Med 179 1994 1597-1604

120 Sebastiani , et-al. Chemokine receptor expression and function in CD4+ T lymphocytes with regulatory activity J Immunol 166 2001 996-1002

121 Enk , Katz Identification and induction of keratinocyte-derived IL-10 J Immunol 149 1992 92-95

122 Melrose , Tsurushita , Liu , Berg IFN-gamma inhibits activation-induced expression of E- and P-selectin on endothelial cells J Immunol 161 1998 2457-2464

123 Kanerva , Alanko Allergic contact dermatitis from 2-hydroxyethyl methacrylate in an adhesive on an electrosurgical earthing plate Eur J Dermatol 8 1998 521-524

124 van der Valk , Devos , Coenraads Evidence-based diagnosis in patch testing Contact Dermatitis 48 2003 121-125

125 Suneja , Belsito Comparative study of Finn Chambers and T.R.U.E. test methodologies in detecting the relevant allergens inducing contact dermatitis J Am Acad Dermatol 45 2001 836-839

126 Lachapelle , et-al. Proposal for a revised international standard series of patch tests Contact Dermatitis 36 1997 121-123

127 Loffler , et-al. Evaluation of skin susceptibility to irritancy by routine patch testing with sodium lauryl sulfate Eur J Dermatol 11 2001 416-419

128 Fregert Manual of Contact Dermatitis ARRAY(0x5e672c)ARRAY(0x5e6750)ARRAY(0x5e67a4)

129 Lachapelle A proposed relevance scoring system for positive allergic patch test reactions: practical implications and limitations Contact Dermatitis 36 1997 39-43

130 Bruze What is a relevant contact allergy? Contact Dermatitis 23 1990 224-225

131 Menne Prevention of nickel allergy by regulation of specific exposures Ann Clin Lab Sci 26 1996 133-138

132 Jensen , Lisby , Baadsgaard , Volund , Menne Decrease in nickel sensitization in a Danish schoolgirl population with ears pierced after implementation of a nickel-exposure regulation Br J Dermatol 146 2002 636-642

133 Schnuch , Geier , Lessmann , Uter Decrease in nickel sensitization in young patients--successful intervention through nickel exposure regulation? Results of IVDK, 1992-2001 Hautarzt 54 2003 626-632

134 Goossens , et-al. Adverse cutaneous reactions to cosmetic allergens Contact Dermatitis 40 1999 112-113

135 De Groot Fatal attractiveness: the shady side of cosmetics Clin Dermatol 16 1998 167-179

136 Hatch , Maibach Textile dye allergic contact dermatitis prevalence Contact Dermatitis 42 2000 187-195

137 Rocha , Silva , Horta , Massa Contact allergy to topical corticosteroids 1995-2001 Contact Dermatitis 47 2002 362-363

138 Corazza , Mantovani , Maranini , Bacilieri , Virgili Contact sensitization to corticosteroids: increased risk in long term dermatoses Eur J Dermatol 10 2000 533-535

139 Veien , Hattel , Laurberg Low nickel diet: an open, prospective trial J Am Acad Dermatol 29 1993 1002-1007

140 Saripalli , Gadzia , Belsito Tacrolimus ointment 0.1% in the treatment of nickel-induced allergic contact dermatitis J Am Acad Dermatol 49 2003 477-482

141 Ruzicka , Assmann , Lebwohl Potential future dermatological indications for tacrolimus ointment Eur J Dermatol 13 2003 331-342

142 Marsland , Griffiths The macrolide immunosuppressants in dermatology: mechanisms of action Eur J Dermatol 12 2002 618-622