COMPARISON OF NATURALLY ACQUIRED AND VACCINE-INDUCED ANTIBODIES TO HAEMOPHILUS-INFLUENZAE TYPE-B CAPSULAR POLYSACCHARIDE

The objective of this study was to assess qualitative differences in t he types of Haemophilus influenzae type B (Hib) capsular polysaccharid e (polyribosylribitol phosphate [PRP]) antibodies induced in children 15 to 27 months of age by (i) natural exposure, (ii) PRP vaccine, and by (iii) PRP-diphtheria toroid conjugate vaccine, (iv) PRP-group B Nei sseria meningitidis outer membrane vesicle conjugate vaccine, and (v) Haemophilus type B oligosaccharide conjugate vaccine (HbOC). The highe st levels of total Hib-PRP antibody measured by radioimmunoassay and i mmunoglobulin G (IgG) measured by enzyme-linked immunosorbent assay we re seen after HbOC immunization. IgG1 Hib-PRP antibodies predominated in all groups, and there were no differences between the groups in the proportion of IgG and IgA Hib-PRP antibodies. However, the proportion s of IgM differed significantly by group. The highest proportions of I gM occurred in naturally acquired antibody and after PRP vaccine, and the lowest proportion occurred after HbOC vaccine. IgG light-chain V k appa II type alpha PRP antibody was present in all groups, and the lev el correlated with the total IgG Hib-PRP antibody level. Therefore, Hb OC induced the highest concentrations of V kappa II type alpha PRP ant ibody, and the naturally acquired antibody group had the lowest levels . IgG light-chain V kappa III antibody levels were also highest in the HbOC group, but there was no correlation between V kappa III antibody levels and total amount of IgG Hib-PRP antibody. These data demonstra te qualitative differences in the antibody repertoires induced by natu ral exposure, the Hib-PRP vaccine, and each of the different Hib conju gate vaccines. We doubt that there are major differences in the protec tion afforded by these different antibody repertoires, because these d ifferences do not appear to correlate with differences in protective e fficacy in older children.