FcgRIIa (CD32): A potential marker defining susceptibility to localized juvenile periodontitis
Studies have indicated that blacks are at greater risk for localized juvenile periodontitis (LJP) compared with other ethnic groups. It also has been noted that LJP may be inherited. Studies show that black LJP patients mount a strong IgG response to Actinobacillus actinomycetemcomitans (A.a.). A large part of this response is mediated by antibodies of IgG2 subclass. Phagocytic cells, particularly neutrophils, are considered to be important in host defense against periodontal bacteria. Not all neutrophils, however, are able to recognize bacteria with IgG2 antibodies. A genetically determined allelic polymorphism as been described for this receptor. H131 binds CD32 efficiently, but the alternative form, R131, does not. Only phagocytes expressing H131 (allotypes of FcgammaRIIa) are able to bind antibodies of this subclass efficiently.
It has been hypothesized in this study that risk for development of LJP in black patients is defined by a propensity toward preferential synthesis of IgG2 antibodies to A.a., together with an increased frequency of the R131 allele of FcgammaRIIa. It has been proposed that individuals who are homozygous for the R131 allele (CD32 allotype expressed on phagocytic cells) would be at greatest risk for this disease given the limited capacity of the receptor allotype to recognize IgG2 antibodies produced in response to infection by A.a. Therefore, the IgG2 cannot bind the R131 efficiently; thus, neutrophils bearing the R131 allotype cannot ingest and destroy the IgG2-affected A.a., placing these individuals at risk of LJP. [I.s.]
Wilson, M.E., and J.R. Kalmer, J Periodont, 67:323, 1996