Department of Dermatology and Allergy, Clinical Research Center for Hair and Skin Science, Charité–Universitätsmedizin Berlin, Berlin, Germany
Department of Dermatology, Medical University of Warsaw, Warsaw, Poland
Department Molecular Diagnostics, Labor Berlin–Charité Vivantes GmbH, Berlin, Germany
Biofilmcenter, Institute for Microbiology, Infectious Diseases and Immunology, Charité–Universitätsmedizin Berlin, Hindenburgdamm 30, 12203 Berlin, Germany
These authors contributed equally
Background: The upper follicular compartment, a well-known reservoir of cutaneous microbiota, constitutes a space for intensive cross-barrier dialogue. The lower follicle comprises the bulb and bulge, structures with relative immune-privileged status, crucial for physiological cycling, and widely considered to be microbial-free. Objectives: Following our initial immunohistochemical screening for regulatory cytokines and defensin expression in anagen hair follicles, we aimed to confirm our results with a follow-up ELISA investigation. We postulated that exposure to microbial components may trigger expression, and thus opted to investigate microbial presence in this area. Materials & Methods: We performed immunohistochemical staining for selected cytokines and antimicrobial peptides, and Gram and Giemsa staining on tissue sections from healthy individuals. Based on ELISA analyses, we confirmed a marked presence of IL-17A- and HBD2 in infrainfundibular compartments from plucked anagen hair follicles of 12 individuals (six females, six males; frontal and occipital scalp sites). 16S rRNA sequencing on microbial DNA extracted from lower follicles, as well as fluorescence in situ hybridization (FISH) were applied to explore bacterial presence in the infrainfundibular compartments. Results: 16S rRNA sequencing yielded reproducible data of bacterial presence in infrainfundibular compartments of plucked scalp follicles; Lawsonella clevelandensis, Staphylococcaceae and Propionibacteriaceae were the most abundant bacteria. Also, FISH revealed biofilm structures formed by Cutibacterium acnes (formerly Propionibacterium acnes) and Staphylococcus sp. below the infundibulum. Conclusion: As the skin microbiome largely influences the local immune system, the presence of bacteria in proximity to follicular immune-privileged areas may be of relevance to hair cycling in health and disease.