Effects of complement inactivation and IgG depletion on skin reactivity to autologous serum in chronic idiopathic urticaria

Abstract

Background: Intradermal injection of autologous serum elicits a wheal-and-flare response in about 60% of patients with chronic idiopathic urticaria (CIU). This reactivity has been attributed to the presence of IgG autoantibodies directed against IgE or the α-chain of the high-affinity IgE receptor (FcϵRIα) expressed on basophils and mast cells, leading to the hypothesis that at least some forms of CIU could be sustained by an autoimmune process. Objectives: The aim of this study was to investigate the relationship between the presence of anti-IgE or anti-FcϵRI antibodies and the ability to induce wheal-and-flare responses in CIU sera selected for the capacity to give a positive skin test response. Methods: Fifteen patients with CIU and a positive skin test response to autologous serum were injected intradermally with native serum and with serum heated at 56°C for 30 minutes and then adsorbed on Sepharose-protein G to obtain IgG depletion. Serum levels of anti-IgE and anti-FcϵRIα antibodies were measured by ELISA by using purified IgE and recombinant RIα-soluble double-fusion protein RIα-human serum albumin-RIα, respectively. The histamine-releasing activity of sera was tested by using ELISA with whole human blood from a healthy donor. Results: All patients had positive cutaneous responses to native serum injection. Anti-FcϵRIα antibodies were present in 14 of 15 native sera, only two of which were able to induce in vitro basophil degranulation. On the contrary, detectable amounts of anti-IgE antibodies were not found in any serum. IgG depletion by protein G resulted in complete (10/14 samples) or considerable (4/14 samples) removal of anti-FcϵRIα antibodies. The two sera endowed with functional activity lost their capacity to trigger histamine release from basophils after heating and protein G adsorption. Nonetheless, heat-decomplemented/IgG-depleted sera elicited wheal-and-flare reactions comparable with those observed with untreated sera. Conclusions: These results strongly suggest that skin reactivity to autologous serum could be due to as yet unidentified non–Ig reactants present in the sera of patients with CIU. (J Allergy Clin Immunol 2000;106:567-72.)