Fca Receptor Iia (Cd32) Heterogeneity In Patients With Recurrent Bacterial Respiratory Tract Infections

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Abstract
Fc-ãRIIa (CD32) is the sole IgG Fc receptor capable ofinteraction with human IgG2, the main IgG subclass of bacterial capsular polysaccharides. The two genetically determined allotypes of human Fc-ãRIIa , Fc-ãRIIa-R131 and IIa-H 131 alleles, have functionally different reactivities with human IgG2. The capacity of polymorphonuclear leukocytes (PMNL) homozygous for Fc-ãRIIa-H/HI31 for IgG2 opsonized bacteria is significantly higher than phagocytosis by PMNL homozygous for Fc-ãRIIa-R/R131, independent of the Fc-ãRIIIb-NA1/NA2 (CDI6) allelic polymorphism. To test the clinical significance of these FcãR polymorphisms, Fc-ãRIIa and Fc-ãRIIIb phenotypes of 48 children with recurrent bacterial respiratory tract infections were determined. Fc-ãRIIa-H/HI31 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-ãRIIa polymorphism may contribute to increased susceptibility to infections with encapsulated bacteria in a childhood population with low IgG2 anti-carbohydrate antibodies.

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