Association between FcγRIIa-R131 allotype and bacteremic pneumococcal pneumonia

Human Fc gamma RIIa has 2 codominantly expressed allotypes, which differ greatly in their ability to ligate immunoglobulin G(2) (IgG(2)). Whereas Fc gamma RIIa-R131 binds only weakly to IgG(2), Fc gamma RIIa-H131 binds to it efficiently and might be primarily responsible for the phagocytosis of IgG(2)-opsonized bacteria. IgG(2) plays a pivotal role in defense against pneumococcal infection. This prospective study showed that 50% of patients with bacteremic pneumococcal pneumonia were homozygous for Fc gamma RIIa-R131, compared with 28% with nonbacteremic pneumococcal pneumonia and 29% of uninfected controls (P < .05). The gene frequency of Fc gamma RIIa-R131 was 0.67 in bacteremic patients, significantly higher than in the other groups (P < .05), All bacteremic patients who died within 1 week of hospitalization were homozygous for Fc gamma RIIa-R131. Therefore, the severity of pneumococcal infection may, in part, be genetically mediated. Taken together with similar findings in cases of meningococcal disease, these results suggest that such genetic factors may be generalizable to infections caused by encapsulated bacteria.