The microbial content and complement C3 cleaving capacity of comedones in acne vulgaris.

: Complement C3 deposition around lesions is an early event in the inflammation of acne vulgaris. The aims of this study were to determine the relationship between the capacity of individual comedones to cleave complement C3 and their microbial flora. The contents of 48 open comedones were expressed from the upper back of acne vulgaris patients and each comedo was homogenized individually and assayed for microbial content and capacity to induce cleavage of complement C3 in an in vitro assay system. An association between Propionibacterium population size and extent of C3 cleavage was found, but Staphylococcus and Pityrosporum population sizes did not appear to have an appreciable influence. A strong association between the weight of expressed material and C3 cleavage was apparent, irrespective of microbial population size. This observation suggests that comedones contain non-microbial material having the capacity to induce complement cleavage and hence initiate inflammation.