Nelydia F. Concepcion

Solid-phase antigen density and avidity of antibodies detected in anti-group B streptococcal type III IgG enzyme immunoassays

Two enzyme immunoassays which measure anti-group B streptococcal type III capsular carbohydrate IgG antibodies were compared. One utilised poly-L-lysine conjugated coating antigen while the other used tyraminated coating antigen. Both carbohydrate antigens appeared to be antigenically identical but the poly-L-lysine based assay gave significantly lower values for some sera. Sera were identified which had low and high avidity anti-group B streptococcal type III IgG antibodies by the thiocyanate elution method. These antibodies gave results on a dilution range of coating concentrations consistent with their relative avidity. Comparison of dilution ranges of the two conjugates used for coating suggests that the poly-L-lysine conjugate coats with a ten-fold lower efficiency than the tyramine conjugate and therefore detects only higher avidity antibodies. Four fractions containing different relative avidities of affinity-purified IgG were produced from a single serum. These fractions behaved in the same manner as sera containing antibodies of different avidities. The results of this study suggest that the method of polysaccharide conjugation in enzyme immunoassays may affect the antigen concentration on the solid phase and thence the detection of antibodies of various avidities.

Demonstration of Opsonic and Protective Activity of Human Cord Sera against Type III Group B Streptococcus that Are Independent of Type-Specific Antibody

ABSTRACT: In an effort to further understand the host defense against group B streptococcus (GBS), we examined 71 human cord sera for their content of type III GBS IgG antibody by enzyme-linked immunosorbent assay and correlated the results with opsonic and protective activity against type III GBS. Most cord sera (67%) containing >0.1 μg/ml of type III GBS IgG antibody promoted phagocytosis and killing in vitro and protection against type III GBS in neonatal rats. However, 26% of cord sera containing <0.1 tig/ml of type III IgG antibody exhibited similar activity in vitro and in vivo against type III GBS. This opsonic and protective activity was retained in IgG fraction of whole serum, and was not directly associated with complement activity or with fibronectin. Further studies are needed to understand the mechanisms responsible for the opsonic and protective activity of some cord sera against type III GBS that may be independent of antibody to the type-specific polysaccharide antigen.

Opsonic Activity of Human IgG and IgM Antibody for Type III Group B Streptococci

ABSTRACT: We separated IgG and IgM from 10 adult sera containing measurable (>0.05 /µg/mL) antibody of both isotypes to the type III polysaccharide of group B streptococci. Ig preparations were used to preopsonize 3Hlabeled type III group B streptococci which were added to adherent monolayers of human, monocyte-derived macrophages. Reproducibly significant phagocytosis, measurable by accumulation of radioactivity and confirmed by electron microscopy, required both antibody (from adult serum or Ig preparation) and complement (from cord serum deficient in specific antibody). All adult IgG and IgM preparations were opsonic in the presence of complement. When a cord serum containing IgG but no IgM antibody was separated by the same procedure, the IgG fraction was opsonic but the fraction that would contain IgM was not. The opsonic activity of IgM in adult sera persisted after the removal of contaminating IgG4. These observations indicate that both IgG and IgM antibody in adult sera are opsonic for type III GBS and support the hypothesis that IgM deficiency in newborns may be a contributing factor to certain bacterial infections.