Immune globulin for intravenous use: enhancement of in vitro opsonophagocytic activity of neonatal serum.

Neonates born with less-than-protective levels of transplacentally derived specific antibody are at risk for the development of disease due to type III, group B Streptococcus (III-GBS). The effect of immune serum globulin modified for intravenous use (MISG) on in vitro opsonophagocytosis of III-GBS was evaluated. Cord blood was obtained from 13 healthy, full-term neonates, and bactericidal activity for III-GBS was measured. Before the addition of MISG, one of three serum specimens with moderate levels of antibody to III-GBS, and eight of 10 specimens with low antibody levels demonstrated no bactericidal activity. The mean bactericidal index increased from 27.1% before the addition of MISG to 96.5% with MISG added in a volume equal to that of serum. The effect of MISG on opsonophagocytosis decreased with its dilution in buffer, and no effect was shown at dilutions greater than or equal to 1:4. Thus, MISG can substantially increase in vitro opsonophagocytosis of III-GBS in sera from newborns.