CHARACTERIZATION OF SPECIFIC IMMUNOGLOBULIN-G (IGG) AND ITS SUBCLASSES (IGG1 AND IGG2) AGAINST THE 23-VALENT PNEUMOCOCCAL VACCINE IN A HEALTHY ADULT-POPULATION - PROPOSAL FOR RESPONSE CRITERIA

The aim of the study was to standardize an enzyme-linked immunosorbent assay (ELISA) method far the quantification of immunoglobulin G (IgG) and its subclasses (IgG1 and IgG2) against the 23-valent pneumococcal vaccine and to establish the criteria for a normal response to the va ccine. Forty healthy individuals (20 women and 20 men; mean age, 29 ye ars) were studied. All were vaccinated with the 23-valent pneumococcal vaccine; blood samples were drawn just prior to and 3 weeks after imm unization, Quantification of specific Ige and its subclasses was perfo rmed by an ELISA with the vaccine as the antigen, The linearity of the ELISA method was demonstrated by the similar slopes of the linear reg ression lines generated from the titration of sera with different anti body concentrations, The specificity of the antibodies against the vac cine was demonstrated by (i) an absorption test with pneumococcal vacc ine, (ii) a cross-reactivity experiment with Haemophilus influenzae ty pe b polysaccharide, and (iii) affinity chromatography with protein A- Sepharose, Response to the vaccine was defined by using the lower leve l of the 90% probability interval (one-tailed) for postimmunization-sp ecific IgG, IgG1, and IgG2, By using this cutoff, responders were cons idered to be those with an absolute increase in antibody titers higher than 395 arbitrary units/ml for IgG, 0.350 A(450) units for IgG1, and 0.314 A(450) units for IgG2, Overall, 20 (50%) subjects had IgG, IgG1 , and IgG2 responses, 9 (22.5%) had Ige and IgG2 responses, 4 (10%) ha d IgG1 responses, 3 (7.5%) had IgG and IgG1 responses, and 4 (10%) wer e nonresponders, Ninety percent of our population responded to the 23- valent pneumococcal vaccine Up to 10% of healthy individuals may respo nd to an IgG subclass without significant increases in total IgG titer s, The ELISA method that is described may be useful for evaluating the specific antibody response against polysaccharides.