In order to understand immunological responses in psoriatic lesions, immunofluorescent findings have been compared in early psoriatic lesions and fully developed plaque lesions. IgG and IgA were detected as the main antibodies in the horny layer by immunohistology. The IgA at the site of leukocyte accumulation in the horny layer seemed to be associated with secretory component (S-component) and joining chian. Regarding complement, the alternate pathway might be related to the immune reaction as the initial response, because deposits of C3, properdin and glycine rich beta-glycoprotein were found more frequently than C1q-deposit in the both lesions. In the dermis S-component was also detected at the dermal papillae adjacent to the dermoepidermal (D-E) junction of the lesions and no deposit of S-component was observed in uninvolved skin of psoriatic patients. This, however, is not a specific pattern in psoriatic lesions since deposits of S-component were found at the dermal papillae and D-E junction in other dermatoses. These findings might suggest that the immunological response was initiated by secretory IgA in horny layer, which was composed of dimeric IgA and S-component at the D-E junction and which passed easily through the epidermal cells.

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