A polyclonal human IgG preparation hyperimmune for type III, group B Streptococcus: in vitro opsonophagocytic activity and efficacy in experimental models.

Neonates at risk for disease due to type III, group B Streptococcus (III-GBS) are those born with low serum levels of transplacentally derived, specific III-GBS antibody. Specific antibody is also required in vitro for opsonophagocytosis of III-GBS. Commercially available human immune serum globulins contain only moderate levels of III-GBS antibody. In the present study, IgG that was isolated from the serum of a human volunteer after vaccination with III-GBS polysaccharide contained very high levels of III-GBS antibody. Small amounts of this hyperimmune preparation added in vitro significantly increased the opsonophagocytosis of III-GBS in neonatal sera in the presence of polymorphonuclear leukocytes. Furthermore, small volumes of the preparation were protective in mouse and neonatal rat models of III-GBS disease. The administration of such hyperimmune human IgG preparations should be considered for preventing or treating III-GBS disease in infants.