Human immunoglobulin G (IgG) Fc receptor IIA (CD32) polymorphism and IgG2- mediated bacterial phagocytosis by neutrophils

Abstract

Human Immunoglobulin G (IgG) Fc receptor IIa (FcγRIIa; CD32) is expressed on phagocytes, triggers phagocytosis, and represents the sole Fc receptor for IgG (FcγR) capable of interaction with IgG2, the main IgG subclass induced in response to bacterial capsular polysaccharides. The two genetically determined structurally different allotypes of human FcγRIIa, the products of the FcγRIIa-R131 and IIa-H131 alleles, have functionally different reactivities with human IgG2. In humans, the FcγRIIa-H131 allotype is known to interact efficiently with complexed human IgG2, whereas the IIa-H131 allotype does so only poorly. This polymorphism may therefore have implications for IgG2-mediated phagocytosis of encapsulated bacteria and susceptibility to bacterial infections. Phagocytosis of IgG2-opsonized bacteria by homozygous FcγRIIa-R/R131, heterozygous Ha-H/R131, and homozygous IIa-H/H131 polymorphonuclear cells (PMN) was compared. A higher phagocytic capacity of IgG2-opsonized group B type III streptococci by PMN of homozygous H/H131 individuals compared with PMN from homozygous R/R131 individuals was observed (P = 0.001), while heterozygous IIa-H/R131 PMN showed intermediate phagocytosis. In this model system, IgG2-mediated phagocytosis was independent of the FcγRIIIb-NA1/NA2 allelic polymorphism.