Functional activities of various preparations of human intravenous immunoglobulin against type III group B Streptococcus.

Two preparations of human immunoglobulin modified for intravenous use (iv immunoglobulin) by different methods (reduction-and-alkylation, or pH 4 treatment) were evaluated for in vitro and in vivo activity against a strain of type III group B Streptococcus (GBS). Both preparations contained similar amounts of total IgG and specific IgG antibody against the type-specific polysaccharide. In vitro, opsonophagocytic studies revealed that pH 4-treated iv immunoglobulin was significantly more effective than reduced-and-alkylated iv immunoglobulin in supporting neutrophil-mediated killing of the type III GBS strain. In vivo, both preparations resulted in similar levels of serum antibody in newborn rats, but pH 4-treated iv immunoglobulin was significantly more protective against the type III GBS strain. This was demonstrated by the lower magnitude of bacteremia, improved survival, and lower protective dose (PD50) in recipients of pH 4-treated iv immunoglobulin. Thus, reduced-and-alkylated iv immunoglobulin was less effective in vitro and in vivo against the strain of type III GBS than was pH 4-treated iv immunoglobulin. Further studies are needed to elucidate the mechanisms for this apparent discrepancy in functional activities of iv immunoglobulin.