IgMand IgA in addition to IgG autoantibodiesagainst FcεRIα are frequent and associated with disease markers of chronic spontaneous urticarial.

BACKGROUND: IgG-autoantibodiesagainst the high affinity IgE-receptor,FceRIα, contribute the pathogenesis of autoimmune chronic spontaneous urticaria (CSU). However, it is not known if such patients also exhibit IgM or IgA autoantibodies against FceRIα. OBJECTIVES: To develop an ELISAto assess serum levels of IgG, IgM andIgA autoantibodies against FceRIα, and to investigateif their presence is linked to clinical features of CSU including the response to autologous serum skin testing (ASST). METHODS: Serum samples of 35 CSU patients (25 ASST-positive) and 52 healthy controlindividuals were analyzed using a newly developed competitive ELISA for IgG, IgM and IgAautoantibodies to FceRIα. RESULTS: One in four CSU patients (8/35, 24%) had elevated serum levels of IgG-anti-FceRIα compared with(3/52, 6%) in healthy controls. More than half of patients had IgM (21/35, 60%) and IgA (20/35, 57%) vs (3/52, 5%) each in healthy controls. ElevatedIgM, but not IgG or IgA autoantibodies, were significantly more frequent in ASST-positive CSU patients (18/25, 72%) compared with ASST-negative patients (3/10, 33%, P =0.022).Also, elevated levels of IgM-anti-FceRIα, but not of IgG or IgA against FceRIα, were linked to low blood basophil(r = 0.414, P = 0.021) and eosinophil(r = 0.623, P < 0.001) counts. CONCLUSIONS: Increased serum levels of IgM-anti-FceRIα are common in patients with CSU and linked to features of autoimmune CSU. The role and relevance of autoantibodies to FceRIα in CSU can and should be further characterized in future studies, and our novel assay can help with this.