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 To-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.