[Chronic urticaria and acquired complement deficiency due to a nephritic factor (C3NeF)].

Several studies have suggested that complement activation processes are frequently involved in the pathogenesis of urticaria. We report clinical evolution and studies of complement-mediated functions in a 47-year-old previously described patient presenting with chronic urticaria, in whom we found persistent low complement hemolytic activity (65-75% of normal values), depressed levels of third complement component (C3, between 55% and 65%) and of factor B (between 60% and 75%), together with C1, C4, C2, C5, C5b neoantigen and fluid phase terminal complement (SC5b-9) complex within the normal range, pointing to activation of the alternative pathway. A circulating low affinity C3 nephritic factor (C3NeF), known to enhance cleavage of human serum C3, was detected. The urticarial lesions, which were initially pruritic and persisted for less than 24 hours, became subsequently fixed and burning, and were accompanied by fever and arthralgia. Skin biopsy specimens showed moderate leukocytoclastic vasculitis. Response to varied treatment regimens, including antihistamines and colchicine, was poor. Therapy with oral corticosteroids produced some improvement. The association of chronic urticaria with C3NeF without clinical and biological signs of membranoproliferative glomerulonephritis and partial lipodystrophy has not to our knowledge been reported before. This observation raises the question of a possible role of C3NeF in the pathogenesis of urticaria.