Immunopathology of pityriasis lichenoides acuta.

Eleven biopsy specimens (five papules and six dusky or crusted lesions) from four patients with pityriasis lichenoides et varioliformis acuta ( PLEVA ) were studied by direct immunofluorescence and immunoperoxidase technics. Slight vascular deposits of IgM and C3 were present in most lesions. Slight perivascular deposits of fibrin were observed in early lesions; more extensive perivascular and interstitial deposits of fibrin were detected in advanced lesions. Most of the infiltrating cells were T lymphocytes; cells with cytotoxic/suppressor phenotype (T8-positive) were generally more numerous than cells with helper/inducer phenotype (Leu-3a-positive, T4-positive). A marked increase in epidermal T8-positive cells over epidermal Leu-3a/T4-positive cells was found in late lesions. Moreover, a reduction of the ratio of circulating T4-positive to T8-positive cells was observed in most cases. The number of epidermal T6-positive (Langerhans/indeterminate) cells was decreased in the lower as compared with the upper stratum spinosum. About 5% of perivascular infiltrating cells were T6-positive. These results suggest that cell-mediated immune mechanisms are probably important in the pathogenesis of PLEVA .