IFN-gamma -positive immunostaining in psoriatic lesional keratinocytes- reply to the comments of McKenzie et al.

ARTICLE

We appreciate the comments of McKenzie et al. on our recent paper on immunohistochemical identification of IFN-gamma -positive cells in psoriatic epidermis. By using our immunohistochemical technique in formalin-fixed, paraffin-embedded sections, we have analyzed IFN-gamma expression in situ in the keratinocytes of various types of skin inflammatory diseases. Four of 6 patients with pustular psoriasis showed positive IFN-gamma staining in keratinocytes. However, IFN-gamma -positive keratinocytes were present in one of 5 in psoriasis vulgaris, one of 4 in acute inflammatory tinea, one of 5 in spongiotic eczematous dermatitis, and one of 6 in lichen planus. There are several possibilities for IFN-gamma immunoreactivity in keratinocytes observed in our study. Keratinocytes could pick up IFN-gamma from the circulation or neighbouring T cells on their surface by binding IFN-gamma to its receptor. The intense staining of IFN-gamma receptor was reported on keratinocytes in psoriasis [1]. Another possible explanation is the production and release of IFN-gamma by keratinocytes. It is not clear why we could detect IFN-gamma expression on keratinocytes in pustular psoriasis more frequently than in other types of skin inflammatory diseases. The IFN-gamma -positive mononuclear lymphoid cells in the epidermis were also obvious in the lesions of pustular psoriasis [2]. IFN-gamma is believed to be an important mediator in psoriasis [3]. The local IFN-gamma expression in epidermis may contribute to the pathogenesis in pustular psoriasis.

References

1. Ackermann L, Harvina IT, Pelkonen J, Ritamaki-Salo V, Naukkarinen A, Harvina RJ, Horsmanheimo M. Mast cell in psoriatic skin are strongly positive for interferon-gamma. Br J Dermatol 1999; 140: 624-33.

2. Koga T, Duan H, Urabe K, Furue M. In situ localization of IFN-gamma positive cells in psoriatic lesional epidermis. Eur J Dermatol 2002; 12: 20-3.

3. Bos JD, De Rie MA. The pathogenesis of psoriasis: immunological facts and speculations. Immunol Today 1999; 20: 40-6.