The immunology of the hair follicle, its relationship with the 'skin immune system' and its role in hair diseases remain biologically intriguing and clinically important. In this study, we analysed the immunoreactivity patterns of 15 immunodermatological markers to determine the cellular composition and immune privilege of the human hair follicle immune system in anagen VI (growth phase). The most prominent cells located in or around the hair follicle were Langerhans cells, CD4+ or CD8+ T cells, macrophages and mast cells, whereas B cells, natural killer cells and gammadelta T cells were found very rarely. Langerhans cells (CD1a+, major histocompatibility complex, MHC class II+), and T cells (CD4+ or CD8+) were predominantly distributed in the distal hair follicle epithelium, whereas macrophages (CD68+, MHC class II+) and mast cells (Giemsa+) were located in the perifollicular connective tissue sheath. Transmission electron microscopy confirmed low numbers of immune cells in the proximal hair follicle epithelium, and very few macrophages and Langerhans cells were seen in the dermal papilla. Melanophages were observed in the connective tissue sheath and dermal papilla. MHC class I (HLA-A, -B, -C) and beta2-microglobulin immunoreactivity was found on most skin cells, but was substantially reduced on isthmus keratinocytes and virtually absent in the proximal hair follicle epithelium. Apart from the absence of Fas ligand immunoreactivity, the sharply reduced numbers of T cells and Langerhans cells, and the virtual absence of MHC class I expression all suggest that the anagen proximal hair follicle constitutes an area of immune privilege within the hair follicle immune system, whose collapse may be crucial for the pathogenesis of alopecia areata.

Overexpression of proinflammatory, type 1 cytokines has been demonstrated in psoriasis and is believed to be of pathophysiological importance. IL-10 is a type 2 cytokine with major impact on immunoregulation, since it inhibits type 1/proinflammatory cytokine formation. Therefore, we investigated its role in psoriasis. We found a relative deficiency in cutaneous IL-10 mRNA expression compared with other inflammatory dermatoses. Interestingly, patients during established antipsoriatic therapy showed higher IL-10 mRNA expression of peripheral blood mononuclear cells than patients before therapy. This suggested that IL-10 may have antipsoriatic capacity. Therefore, we performed a phase 2 pilot trial with subcutaneous IL-10 administration (8 microg/kg/d) over 24 d in three patients. Clinical efficiency measured by objective and subjective parameters was found. Immunosuppressive effects (depressed monocytic HLA-DR expression, TNF-alpha and IL-12 secretion capacity, IL-12 plasma levels, and responsiveness to recall antigens) as well as a shift toward a type 2 cytokine pattern (increasing proportion of IL-4, IL-5, and IL-10 producing T cells, selective increase in IgE serum levels) were observed. Remarkably, IL-10 administration also enhanced the intracutaneous IL-10 mRNA expression. Our investigations demonstrate the major importance of IL-10 in psoriasis and show that IL-10 administration represents a new therapeutic approach. This is the first report on IL-10 therapy for cutaneous disorders.

The results obtained are similar to those of human skin, indicating the suitability of this porcine tissue as a model for human skin.

Summary Background  Patients with rheumatic diseases receiving antitumour necrosis factor (TNF)‐α‐based treatment may develop cutaneous reactions. Objectives  To analyse the new onset or aggravation of skin lesions in patients with a rheumatic disease during treatment with TNF‐α antagonists. Methods  We conducted a prospective analysis of 35 of 150 patients with a long history of rheumatic disease, including rheumatoid arthritis, ankylosing spondylitis (Bechterew's disease) and psoriatic arthritis, to test for the development of cutaneous manifestations during anti‐TNF‐α (infliximab, adalimumab or etanercept) treatment. Results  Chronic inflammatory skin diseases such as psoriasis and eczema‐like manifestations represented the majority of cases (16 of 35). Cutaneous infections caused by viral, bacterial and fungal agents were also observed in many patients (13 of 35). Skin diseases such as dermatitis herpetiformis, leucocytoclastic vasculitis and alopecia occurred in single cases only. Conclusions  We observed a broad, diverse clinical spectrum with a majority of chronic inflammatory and infectious skin diseases. However, we did not identify individual risk factors and a discontinuation of the anti‐TNF‐α treatment was not necessary if adequate dermatological treatment was performed. The onset of cutaneous side‐effects in anti‐TNF‐α‐based treatments should be determined by nationwide registries.