Complement deposits in epidermal cells after ultraviolet B exposure

Ultraviolet B (UVB) radiation is known to induce formation of sunburn cells (SBC) in the epidermis. Since it was unknown whether this process might be accompanied by complement (C) activation, we analyzed C-deposition in skin biopsies taken before and 24 h and 48 h after UVB exposure (fourfold minimal erythema dose or fourfold minimal phototoxic dose) from 14 patients (5 receiving potentially photosensitizing drugs and 9 without such medication) by immunohistology. Local C-activation was visualized by direct or indirect immunofluorescence staining with polyclonal antibodies against C3b, C3d, C5, C9 and monoclonal antibodies to C3b, C3d, C9 and neoantigens on the terminal complement complex (TCC). Neutrophils were identified immunohistologically by antibodies to polymorphonuclear elastase. All but one specimen taken before UVB irradiation were completely negative; biopsies obtained 24 h after UVB revealed complement C3b- and/or C3d-deposits within scattered cells of the epidermis, with wide individual variations in the number of C3-positive cells. C3b and TCC were found predominantly in the cytoplasma; C3d deposits were more often accentuated at the cell surface of C-positive cells. A significantly higher number of keratinocytes was C3d-positive 48 h after UVB exposure than in specimens taken 24 h after UVB. Such a reactivity pattern might indicate a rapid decay of intracellular C3b to C3d. Patients medicated with potentially photosensitizing drugs developed significantly higher numbers of strongly C3-positive cells than those without such medication. Infiltration with elastase-positive cells, presumably representing neutrophils, was observed in the upper third of the dermis and the epidermis in all but one biopsy (n = 9) after UVB.(ABSTRACT TRUNCATED AT 250 WORDS)