Activation of complement by Pityrosporum orbiculare.

The ability to activate complement in human serum was evaluated for the two yeast-like organisms Pityrosporum orbiculare, the presumed etiologic agent of tinea versicolor, and Candida albicans. Complement activation was measured by: (a) using inhibition of rabbit red blood cell lysis by human serum after incubation with the organisms, and (b) quantitation of the amount of C3 deposited on the surface of the yeast by an enzyme-linked immunoabsorbent assay. It was found that both organisms had approximately equal ability to activate complement in normal serum or serum having only the alternative pathway intact, even though extracts of C. albicans contained significantly greater amounts of both carbohydrate and antigenic material capable of combining with the antibody present in normal human serum. The marked difference in inflammation in the cutaneous lesions produced by these two organisms does not appear to be related to their complement-activating ability and is more likely due to some other factor such as differences in invasiveness or in ability to elicit other immunologic reactions.