An immunologic and cultural study of Pityrosporum folliculitis.

In patients with Pityrosporum folliculitis the mean serum antibody titer against Pityrosporum orbiculare was significantly higher than in healthy control subjects (p less than 0.01). The mean number of P. orbiculare organisms per square centimeter cultured from normal-looking skin in patients was not significantly higher than the number cultured from normal-looking skin in control subjects. Results of prick tests against P. orbiculare extract were negative or weak, indicating that patients with Pityrosporum folliculitis had no type I hypersensitivity against P. orbiculare. Immunohistochemical staining of skin lesions showed perivascular dermal cell infiltrates near the hair follicles dominated by anti-Leu 3a-reactive T lymphocytes. Human lymphocyte antigens with the DR locus, but not those with the DQ locus, on keratinocytes were observed in one case.