Mast cell is a major key effector in the pathogenesis of chronic spontaneous urticaria (CSU) and activated by not only IgE but also circulating FcεRI-specific IgG antibody. This study aimed to measure circulating IgG to FcεRIα in sera of CSU patients.

Eighty-eight patients with CSU and 76 healthy controls (HCs) were enrolled. To detect circulating IgG to FcεRIα level by ELISA, the novel IgE_TRAP called YH35324 was used to bind to the FcεRIα site of each serum autoantibodies including IgG. The results of autoantibodies in patients with CSU were compared to the ELISA results using recombinant FcεRIα. ELISA inhibition test with the addition of YH35324 confirmed its binding specificity. The IgG levels were measured and presented by the ratio of signal pre-incubated with IgE_TRAP to mock-incubated one, and the lower ratio of IgG implied the higher levels of FcεRI-specific IgG. The autoimmune group was defined if CSU patients had positive results to ASST and/or ANA. Clinical and autoimmune parameters including atopy, urticaria activity score (UAS), serum total/free IgE levels, serum antinuclear antibody (ANA) and autologous serum skin test (ASST) were assessed. 

The ratio of serum IgG to FcεRIα was significantly lower in patients with CSU than in HCs (P<0.05), while no differences were noted in serum levels of IgG to recombinant FcεRIα autoantibodies. The autoimmune CSU group had significantly lower ratios of IgG autoantibodies to FcεRIα than the nonautoimmune CSU group (P=0.02). No significant associations were found between the presence of IgG antibodies and sex, age, atopy, urticaria duration, UAS, or serum total/free IgE levels. 

The present study confirmed the presence of circulating autoantibodies, IgG to FcεRIα in sera of CSU patients, especially in the patients related to autoimmunity.