Respiratory syncytial virus-specific immunoglobulins in preterm infants.

Incomplete transfer of maternal antibodies specific to respiratory syncytial virus (RSV) has been suggested as an explanation for the increased risk of RSV infections in preterm infants. Antibodies directed against the two major RSV envelope glycoproteins, F and G, are protective in vitro and in vivo. Our study was conducted to measure IgG, IgG1, IgG2, and IgG3 antibody titers against the RSV F and G glycoproteins in cord sera from infants born at different gestational ages. Titers of neutralizing antibody were measured in a subset of the subjects. The mean (+/- SEM) log2 titers of IgG antibodies directed against the RSV F and G glycoproteins were significantly lower in infants born at < or = 28 weeks of gestation (11.2 and 10.8 for F and G glycoproteins, respectively) than in term infants (12.6 and 12.8 for F and G, respectively) (p < 0.05). Preterm infants born at > or = 29 weeks had titers of antibodies against the F glycoprotein comparable to those of term infants. The highest titers of RSV-specific antibodies were in the IgG1 and IgG2 subclasses. Mean (+/- SEM) neutralizing antibody titers were lower in infants born at < or = 28 weeks (7.7 +/- 0.4) than in term infants (10.2 +/- 0.3) (p < 0.001). We conclude that (1) RSV-specific antibody titers were lower than in term infants only in the most premature infants (< or = 28 weeks) and (2) preterm infants born at > or = 29 or > or = 33 weeks of gestation had RSV-specific titers against F and G glycoproteins, respectively, that were comparable to those of term infants. Preterm infants born at < or = 28 weeks could represent a target population for passive immunoprophylaxis.