SEVERITY OF INFECTIONS IN IGA DEFICIENCY - CORRELATION WITH DECREASEDSERUM ANTIBODIES TO PNEUMOCOCCAL POLYSACCHARIDES AND DECREASED SERUM IGG2 AND OR IGG4/

In order to define abnormalities of humoral immunity which determine s usceptibility to respiratory tract infections in IgA-deficient adults, serum IgG subclass concentrations, and serum concentrations of pneumo coccal antibodies and Haemophilus influenzae type B (Hib) antibodies s era from IgA-deficient adults with and without susceptibility to respi ratory tract infections were compared. Infection susceptibility was no t related to the degree of IgA deficiency, but was related to deficien cy of IgG4 and, to a lesser extent, IgG2, as well as to low basal seru m concentrations of pneumococcal polysaccharide antibodies. The combin ation of IgG2 and/or IgG4 deficiency and a non-protective basal serum concentration of antibody against two or more pneumococcal polysacchar ides was present in the serum of six of 12 (50%) patients with severe infections, but only one of 44 (2%) patients without infections. Furth ermore, the preservation of antibody responses against the most immuno genic pneumococcal polysaccharide type 3, but not against the less imm unogenic types 7F, 9N and 14, in patients with severe infections sugge sted that abnormalities of pneumococcal polysaccharide antibody respon ses might include defects of affinity maturation.