Enhanced IgG1 and IgG3 responses to pneumococcal polysaccharides in isolated IgA deficiency.

Serum IgG subclass-specific antibody concentrations to pneumococcal polysaccharides (PnPs) 1 and 14 were measured in 13 adult patients with isolated IgA deficiency and nine healthy adults immediately before and 4 weeks following immunization with polyvalent pneumococcal vaccine. Samples were analysed by enzyme immunoassay using pooled human serum as a reference preparation. A significant rise in median post-immunization antibody concentrations to PnPs14 was seen for all IgG subclasses, for IgA-deficient patients and for controls. For PnPs1, post-immunization IgG2 and IgG4 antibody concentrations rose significantly in the patient group, and IgG4 antibody concentrations rose significantly in the controls. The median IgG1 and IgG3 antibody concentrations to PnPs1 were significantly higher pre- and post-immunization in IgA-deficient individuals in comparison with controls, as were post-immunization IgG3 antibody concentrations to PnPs14. This enhancement of IgG1 and IgG3 antibody responses to pneumococcal polysaccharide antigens in IgA-deficient patients suggests an alteration in regulation of the normal switching processes in the generation of subclass and isotype diversity or could possibly be due to alteration in the affinity of subclass specific antibody.