Several lines of evidence suggest that passive immunization as adjunctive therapy for or prevention of group B streptococcal (GBS) sepsis in neonates will require the use of preparations of human intravenous immune globulin (IVIG) that are hyperimmune for protective antibodies to GBS. Results from both in vitro and in vivo experiments utilizing commercially available IVIG preparations suggest that the doses
necessary for achieving levels of pathogen-specific antibody capable of promoting efficient opsonization and phagocytosis of GBS may be prohibitive. Several laboratories have reported that standard IVIG preparations contain only modest levels of antibodies to the four capsular polysaccharides of GBS (the protective moieties), are variable in their effect on in vitro opsonophagocytosis by dose and method of preparation, and are significantly less protective in animal models than is IVIG prepared from adults immunized with GBS polysaccharide vaccines. Further, when we gave a single infusion of standard IVIG at a dose of either 500 or 750 mg/kg to 10 premature neonates during the first week of life, opsonophagocytosis of type III GBS by their sera and adult neutrophils was observed only when high levels of specific antibody were achieved, levels only transiently achieved in nonimmune infants. Commercial preparation of human immune globulin hyperimmune for GBS will be required for optimal adjunctive therapy in patients with sepsis due to GBS and for the possible prevention of late-onset infant disease.