IMMUNOHISTOCHEMICAL IDENTIFICATION OF TYPE-II ALTERNATIVELY ACTIVATEDDENDRITIC MACROPHAGES (RM-3 1(+++), MS-1(+/-), 25F9(-)) IN PSORIATIC DERMIS/

Immunological mechanisms play an important role in the pathogenesis of psoriasis. Lesional psoriatic skin-derived T-cell clones have been sh own to stimulate keratinocyte proliferation and to predominantly expre ss a T-helper type 1 cytokine pattern. However, T-helper type 2-like c ytokines have also been identified in some psoriatic T-cell clones. In parallel to the T-helper type 1/type 2 dichotomy, a distinction betwe en interferon-gamma-induced (classically activated) macrophages and in terleukin-4/glucocorticoid-induced (alternatively activated) macrophag es has been put forward as a conceptual framework for a better underst anding of immunopathological processes. In the present study, the phen otype of mononuclear phagocytes in psoriatic skin lesions (n = 21), al lergic contact dermatitis (n = 4) and normal skin (n = 2) was investig ated using a panel of monoclonal antibodies (mAb) against monocytes/ma crophages and dendritic cells (mAb MS-1, RM 3/1, and 25F9 against subs ets of in vitro alternatively activated macrophages, and mAb against m yeloid antigens CD1a, CD11b, CD11c, CD34, CD36, and CD68). With regard to mononuclear phagocytes, psoriatic skin was found to be compartment alized into epidermis, subepidermal space, and upper and lower dermis. RM 3/1(+++), MS-1(+/-), 25F9(-) dendritic macrophages previously clas sified as type II alternatively activated macrophages were the dominan t dermal macrophage population in psoriatic skin, while intraepidermal and epithelium-lining macrophages expressed a different, presumably c lassically activated, macrophage phenotype (RM 3/1(-), MS-1(-), 25F9(- ), CD68(++), CD11b(++)). In allergic contact dermatitis, a classical T -helper type 1 disease, RM 3/1(+++) macrophages were less prominent. S ince MS-1 high molecular weight protein is much more sensitive to inte rferon-gamma-induced suppression than RM 3/1 antigen, a predominance o f T-helper type 1 cytokines in psoriasis could explain why dermal dend ritic macrophages do not express the fully induced MS-1(+++), RM 3/1(++), 25F9(+/-) phenotype of type I alternatively activated macrophages .