Antibody class and subclass responses to pneumococcal polysaccharides following immunization of human...

Antibodies of the IgM class and IgG2 and IgA2 subclasses are prominent in responses to pneumococcal polysaccharides (PPS) but may be decreased in human immunodeficiency virus (HIV)-infected patients, among whom invasive pneumococcal disease is common. After immunization of HIV-infected and -seronegative subjects with pneumococcal vaccine, the number of PPS-specific antibody-secreting cells (ASC) producing IgM was significantly lower among HIV-infected subjects, whereas PPS-specific IgG and IgA ASC were more comparable. The subclass distribution of PPS-specific IgG2-producing (approximately 80%) and IgA2-producing (approximately 50%) ASC and antibodies in serum were similar. However, before immunization, the proportions of PPS-specific IgG2 for both serotypes 8 and 14 in baseline sera from HIV-infected patients were significantly decreased compared with controls. Thus, the response to PPS among HIV-infected patients may be characterized by lower levels of specific IgG2 before immunization and prominent defects in IgM responses soon after stimulation.