Using an indirect double layer immunofluorescence method, fresh skin lesions of 10 patients with different forms of cutaneous vasculitis were tested for the occurrence of complement-factors C1q (C1), alpha2D(C3) and beta1F (C5). In contrast to the irregularly found complement fixing immunoglobulins IgG and IgM, complement could be regularly seen bound to the cutaneous vessel walls; mostly the C3-factor alpha2D. C1q was demonstrable, combined with IgG and/or IgM only in 2 cases. In 5 patients there was a non-homogenous, roddy fluorescenece of the epidermal basal membrane zone and the cutaneous vessels, when alpha2D or beta1F were tested. Our findings suggest that the "alternate pathway" beginning with C3-activation is followed in most cases, whereas a typical "immune complex vasculitis" is obviously rare. The constant occurrence of complement in the cutaneous vessel walls of vascultis lesions is consistent with the known chemotactic and destructive role of complement factors in experimental models of angiitis, but it may not necessarily involve a specific immunological process.
