Human-isotype-specific enzyme immunoassay for antibodies to pneumococcal polysaccharides.

A simple enzyme immunoassay has been developed to allow the quantitation of the human response to immunization with pneumococcal polysaccharide. The assay uses the 14-valent vaccine (Pneumovax) as a convenient antigen to adsorb to the solid-phase microdilution plate wells and commercially available isotype-specific antibody conjugates. The results have been expressed as arbitrary pneumococcal polysaccharide antibody units by reading off a standard curve constructed by using heterogeneous pooled serum. All nonimmunized subjects tested had immunoglobulin G (IgG) antibodies present in serum. All six control subjects who were immunized with Pneumovax demonstrated an IgG response, and the majority responded with a rise in IgA- and IgM-specific antibody concentrations at a mean of 6 weeks postimmunization. Five out of six cord sera tested contained IgG antibodies only, which were present in concentrations similar to those seen in adults, whereas in 6- to 12-month-old infants only low levels of IgG and IgM and no IgA antibodies were detected. Serum taken from 10 hypogammaglobulinemic patients immediately prior to infusion of immunoglobulin showed low to negative IgG antibody concentrations, and no IgA or IgM antibody was present.