Allergen-specific IgG1 and IgG3 through FcγRII induce eosinophil degranulation

Evidence suggests that eosinophils contribute to inflammation in bronchial asthma by releasing chemical mediators and cytotoxic granule proteins. To investigate the mechanism of eosinophil degranulation in asthma, we established an in vitro model of allergen-induced degranulation. We treated tissue culture plates with short ragweed pollen (SRW) extract and sere from either normal donors or SRW-sensitive patients with asthma. Eosinophils were incubated in the wells and degranulation was assessed by measurement of eosinophil-derived neurotoxin in supernatants. We detected degranulation only when sere from SRW-sensitive patients were reacted with SRW. Anti-IgG and anti-Fc(γ)RII mAb, but not anti-IgE or anti-Fc(ε)RII mAb, abolished the degranulation. IgG-depleted serum did not induce degranulation; IgE-depleted serum triggered as much degranulation as untreated serum. Furthermore, serum levels of SRW-specific IgG1 or IgG3 correlated with the amounts of released eosinophil-derived neurotoxin. When eosinophils were cultured in wells coated with purified IgG or IgE, eosinophil degranulation was observed only with IgG. Finally, human IgG1 and IgG3, and less consistently IgG₂, but not IgG4, induced degranulation. Thus, sera from patients with SRW-sensitive asthma induce eosinophil degranulation in vitro through antigen-specific IgG1 and IgG3 antibodies. These antibodies may be responsible for degranulation of eosinophils in inflammatory reactions, such as bronchial asthma.