IgG2 antibody is the essential subclass to protect against encapsulated bacteria FcγRlla is the only Fcγ receptor that interacts with human IgG2. The two genetically determined allotypes of human FcγRlla, FcγRlla-R131 and FcγRlla-H131 alleles have functionally different reactivities with IgG2 in vitro, and H/H-131 cells have markedly higher binding affinity for human IgG2. Homozygous FcγRllb-NA1/NA1 PMNLs show higher phagocytic capacity than FcγRllb-NA2/NA2 PMNLs. To evaluate in vivo significance of FcγRlla and FcγRllb allotypes, we analyzed FcγR allotypes in children with bacterial meningitis due to Haemophilus influenzae type b, Streptococcus pneumoniae and Neisseria meningitidis. FcγRll and FcγRllb polymorphisms were determined by using quantitative flow cytometry. FcγRlla were studied in 23 children with bacterial meningitis and 50 healthy Turkish controls, and Fcγllb in 18 and 43 such individuals, respectively. The distribution of FcγRlla in the healthy Turkish control group was found to be significantly different from that in the Chinese and Japanese population (p<0.05), but similar to that of the white population in the USA and the Netherlands. No case (0%) had the FcγRlla-H/H-131 FcγRllb-NA1/NA1 the corresponding figure in the controls was 4 (9.3%). Homozygous FcγRlla-H/H-131 phenotype was underrepresented with borderline significance (p: 0.057) in patients below two years of age in comparison with the healthy subjects and with patients with meningitis over two years of age (p: 0.059). Although the study needs to be conducted in a large series of patients in order to draw a firm conclusion, FcγRlla polymorphism may be a contributing factor to the increased susceptibility to meningitis with encapsulated bacteria in children below two years of age.

Keywords: FcγR allotypes, bacterial meningitis