Fc gamma receptor IIa (CD32) heterogeneity in patients with recurrent bacterial respiratory tract infections.

Fc gamma RIIa (CD32) is the sole IgG Fc receptor capable of interaction with human IgG2, the main IgG subclass of bacterial capsular polysaccharides. The two genetically determined allotypes of human Fc gamma RIIa, Fc gamma RIIa-R131 and IIa-H131 alleles, have functionally different reactivities with human IgG2. The capacity of polymorphonuclear leukocytes (PMNL) homozygous for Fc gamma RIIa-H/H131 for IgG2 opsonized bacteria is significantly higher than phagocytosis by PMNL homozygous for Fc gamma RIIa-R/R131, independent of the Fc gamma RIIb-NA1/NA2 (CD16) allelic polymorphism. To test the clinical significance of these Fc gamma R polymorphisms, Fc gamma RIIa and Fc gamma RIIIb phenotypes of 48 children with recurrent bacterial respiratory tract infections were determined. Fc gamma RIIa-H/H131 was less than half that observed in 123 healthy adults (P = .01). IgG2 responses were low in 25 of 48 patients after immunization with pneumococcal vaccine. These results suggest that Fc gamma RIIa polymorphism may contribute to increased susceptibility to infections with encapsulated bacteria in a childhood population with low IgG2 anti-carbohydrate antibodies.