Specific IgG subclass antibody levels and phagocytosis of serotype 14 pneumococcus following immunization

Complement and specific antibody directed against capsular polysaccharide are necessary for efficient phagocytosis of pneumococci. In normal adults, specific antibody to pneumococci is predominantly of the IgG2 subclass. However, the role of IgG2 in bacterial clearance is debatable. We therefore decided to investigate the relationship between specific IgG subclass antibody levels and phagocytosis of serotype 14 pneumococcus, before and after immunization with a pneumococcal capsular polysaccharide vaccine. Specific IgG subclass antibody was measured by an ELISA technique and the effect of serum on phagocytosis of radiolabelled pneumococci by normal polymorphs was determined. We found that in the presence of complement, phagocytosis correlated significantly with both specific IgG1 and IgG2 antibody titres (r = 0.547, P = 0.002 and r = 0.464, P = 0.009, respectively). However, in decomplemented sera, the correlation with IgG1 antibody was lost, whereas that with IgG2 antibody was strengthened (r = 0.641, P = less than 0.001). The possibility that IgG2 binds to receptors on polymorphs should be considered.