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It is believed that DOPA-negative melanocytes in the outer root sheath of the human hair follicle are activated, become identifiable by DOPA staining, and migrate into the epidermis during the repigmenting phase of vitiligo. These cells are difficult to identify, however, and otherwise have not been characterized. These cells are readily identified by immunofluorescence, immunohistochemistry, and immunoelectronmicroscopy using the antibodies NKI/beteb and A4F11, which recognize premelanosome-related antigens. The majority of the outer root sheath melanocytes were found in the mid to the upper portion of the hair follicle. Double staining revealed that these cells were distinct from HLA-DR-bearing dendritic cells. Further immunohistochemical investigation using alpha-PEP-7, alpha-PEP-1, or TMH-1 and alpha-PEP-8 antibodies revealed that outer root sheath melanocytes cannot be identified by antibodies to tyrosinase, TRP-1, or TRP-2, respectively. These cells also did not react with HMB45 antibody, which recognizes a melanosome-associated cytoplasmic antigen. We believe that the inactive outer root sheath melanocytes contain some of the early structural proteins but not any of the enzymatic proteins necessary for melanogenesis. Therefore, activation is the process whereby outer root sheath melanocytes acquire all of the structural and enzymatic proteins necessary for melanogenesis.

We found distinct patterns of intercellular adhesion molecule-1 (ICAM-1) expression in three diseases characterized by interface dermatitis with mononuclear infiltrates and keratinocyte cytotoxicity: lichen planus (LP), subacute cutaneous lupus erythematosus (SCLE), and erythema multiforme (EM). In LP, basal keratinocytes show strong ICAM-1 expression associated with a dermal infiltrate, but ICAM-1 expression in the rest of the epidermis is minimal. In SCLE, there is diffuse epidermal ICAM-1 expression, sometimes with accentuation on the cell surface of basal cells. In EM, there is strong basal cell expression of ICAM-1 with evident cell surface accentuation, and also pockets of suprabasal expression with cell surface accentuation. These patterns are associated with different factors that trigger cytokine release in different locations. Both tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) produce greater relative ICAM-1 expression in basal keratinocytes than in more differentiated keratinocytes. In LP, the pure basal keratinocyte expression of ICAM-1 appears to be caused by cytokines, predominantly IFN-gamma, released by dermal lymphocytes. The pattern of ICAM-1 in SCLE corresponds to the pattern induced by ultraviolet radiation (UVR): diffuse epidermal ICAM-1 expression, sometimes with basal accentuation. Some individuals are "responders" to TNF-alpha or UVR, showing high levels of ICAM-1 expression following UVR or TNF-alpha stimulation in vitro or UVR stimulation in vivo. We propose that the pattern of ICAM-1 induction in SCLE is dependent on UVR-induced TNF-alpha release. EM is associated with apparent latent Herpes simplex virus, and Herpes simplex virus (HSV)-infected keratinocytes show enhanced ICAM-1 expression. We propose that in EM suprabasal ICAM-1 expression may be induced directly by HSV infection or indirectly through TNF-alpha release induced by HSV reactivation. Induction of ICAM-1 within the epidermis is stratified and individually variable. Basal keratinocytes show maximal induction of ICAM-1 expression due to innate sensitivity to TNF and IFN-gamma stimulation, and to location adjacent to dermal sources of cytokines. Suprabasal ICAM-1 can be induced by UVR and epidermal TNF-alpha release, and by factors such as viral infection. Different triggers of cytokine release and adhesion molecule induction may influence the different patterns of inflammation seen in diverse inflammatory skin diseases.

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