Complement deposition in the skin of patients with herpes-associated erythema multiforme.

Granular staining for C3 by direct immunofluorescence is a frequent finding along the dermoepidermal junction and in papillary blood vessels in the early skin lesions of erythema multiforme. In order to evaluate whether the complement cascade is activated by the classical or alternative pathway, ten biopsies from patients with herpes-associated erythema multiforme, which were positive for granular C3 along the dermoepidermal junction, were stained by an immunofluorescence technic for other complement components. Staining for the components of classical pathway, C1q and C4, were found in none of the ten biopsies. However, in nine of ten biopsies, granular staining for properdin was present along the dermoepidermal junction. These findings suggest complement activation by the alternative complement pathway in herpes-associated erythema multiforme.