Contribution of serotype-specific IgG concentration, IgG subclasses and relative antibody avidity to opsonophagocytic activity against Streptococcus pneumoniae

Abstract

SUMMARYThe contribution of serotype-speci®c IgG concentration, subclasses, and avidity to opsonophagocytic activity (OPA) against Streptococcus pneumoniae (Pnc) was evaluated in sera of adults and infants immunized with different pneumococcal vaccines. Antibody concentrations and avidities were measured by enzymeimmunoassay (EIA) and OPAs by killing assay of Pnc. The most important factor contributing positively to OPA was the speci®c IgG level. In infants, a tendency to negative correlation was found between the concentration needed for killing of bacteria and avidity, suggesting that less antibodies of high rather than low avidity were required for killing. No such correlation was seen in adults. However, in adults the avidity was high already before vaccination and the variation was narrow. Thus, avidity was probably not a limiting factor in¯uencing OPA. The effect of IgG2/IgG1 ratio on OPA was mostly negative but insigni®cant.

Specificities and Opsonophagocytic Activities of Antibodies to Pneumococcal Capsular Polysaccharides in Sera of Unimmunized Young Children

“…However, for the estimation of immunity, a good correlation between the concentration of immunoglobulin G (IgG) measured by EIA and the OPAs of antibodies is needed. The correlation between the two methods has been reasonably good with postimmunization serum samples from infants and adults (1,13,21,22). However, sera from unimmunized individuals may have lower OPAs than expected on the basis of the antibody concentration obtained by EIA (1,11).…”

Opsonophagocytic activity against Streptococcus pneumoniae type 19F in allogeneic BMT recipients before and after vaccination with pneumococcal polysaccharide vaccine

“…In some cases polyreactive, non-specific antibodies with low functional activity can be detected by the EIA method, and explain the undetectable OPA in sera with high specific IgG levels. 29 In the study of Anttila and co-workers, 26 OPA against Pnc serotypes 6B, 19F and 23F was not detectable in most of the sera drawn from healthy adults without vaccination with Pnc vaccines whereas after immunization with plain Pnc PS or Pnc conjugate vaccines OPA was detectable in all serum samples. The IgG antibody concentrations to Pnc 19F showed a high degree of correlation with OPA, r values being 0.70 and 0.88 before and after vaccination, in contrast to 0.51 and 0.52 before and after vaccination in our study, respectively.…”

“…In normal adults the OPA of antibodies to Pnc serotypes 6B, 14, 19F, and 23F correlates with specific IgG, IgG1 and IgG2 antibody levels, but not with specific IgA and IgM levels. [26][27][28] IgG anti-19F PS concentrations у1-2 g/ml are needed to detect the OPA by the methodology we used. 26 In this study the 12 BMT recipients showing any response to Pnc PS vaccine achieved low IgG anti-19F concentrations.…”

“…[26][27][28] IgG anti-19F PS concentrations у1-2 g/ml are needed to detect the OPA by the methodology we used. 26 In this study the 12 BMT recipients showing any response to Pnc PS vaccine achieved low IgG anti-19F concentrations. This may partly explain the fact that regardless of IgG anti-19F increases there were no changes in the OPA in many cases.…”

“…25 The lower detection limit for IgG anti-19F was 0.17 g/ml. OPA against type 19F pneumococcus was determined by a killing assay using fresh human polymorphonuclear leucocytes and baby rabbit complement as described by Anttila et al 26 OPAs are expressed as titres: OPA is the reciprocal of the serum dilution with 50% killing as compared to the bacterial growth in controls without serum. A titre of 4 was given to sera with undetectable OPAs, the titre of 8 being the lowest positive result.…”