Lower antibody response to Porphyromonas gingivalis associated with immunoglobulin G Fcγ receptor IIB polymorphism

Human Fc gamma RIIB is one of the receptors for immunoglobulin G (IgG) and suppresses the activation of B lymphocytes through cross-linking with the B cell receptor via immune complexes. This function of Fc gamma RIIB is essential for the negative regulation of antibody production. Our previous study has demonstrated the gene polymorphism Fc gamma RIIB-I232T to be associated with periodontitis. The polymorphism Fc gamma RIIB-232T has been reported to inhibit B-cell antigen receptor signaling more effectively compared to Fc gamma RIIB-232I, while other groups concluded that Fc gamma RIIB-232T had no ability to inhibit activatory receptors. In this study, we examined whether Fc gamma RIIB-I232T polymorphism would change the IgG antibody response to the periodontopathic bacteria Porphyromonas gingivalis. Forty-seven patients with periodontitis were genotyped with the direct sequencing of genome DNA. Serum IgG and specific IgG subclass levels for the sonicate of P. gingivalis and the recombinant 40 kDa outer membrane protein (OMP) were determined. No significant difference in the total IgG level and IgG response to P. gingivalis sonicate were observed between sera from Fc gamma RIIB-232T carriers and non-carriers. The Fc gamma RIIB-232T carriers revealed a significantly lower IgG(2) response to P. gingivalis 40 kDa OMP compared to non-carriers (p = 0.04, Mann-Whitney U-test). Lower responses of Fc gamma RIIB-232T carriers were also observed in specific IgG and IgG(1) levels. The Fc gamma RIIB-232T carriers revealed a low level of IgG(2) response to P. gingivalis 40 kDa OMP, even with a high average probing pocket depth. These results suggest that association of the Fc gamma RIIB-232T allele with periodontitis might be related to the lower levels of antibody response to P. gingivalis.