[Circulating immune complexes and necrotizing vasculitis]

55 patients with necrotizing and with various forms of lymphocytic vasculitis were investigated for the presence of vascular deposits of immunoglobulins (Ig) and C3 by immunofluorescence testing of skin biopsies and with a 125I-Clq-binding assay for the presence of circulating immune complexes. Vascular deposits of Ig and C3 were found frequently both in patients with necrotizing and with lymphocytic vasculitis. In contrast, C1q binding activity was found almost exclusively in sera of patients with systemic necrotizing vasculitis. With one exception, all sera with C1q binding activity were from patients with vascular deposits of Ig and C3. The implications of these findings for our understanding of the development of system involvement in necrotizing vasculitis are discussed.