Kinetics of phagocyte response to group B streptococcal infections in newborn rats

Abstract

Inadequate in vivo mobilization of leukocytes may contribute to the unique susceptibility of neonates to infection. Kinetics of the phagocyte response of neonatal and adult rats to i.p. infection with group B Streptococcus, type Ia were studied. LD50 was considerably greater for adults than for neonates (1.1 .times. 107 colony-forming units [CFU]/g vs. 2.7 .times. 102 CFU/g). After challenge with group B Streptococcus, type Ia, the number of neonatal peritoneal leukocytes increased more slowly than did those of adult rats. At 4 h, the adult neutrophil count was 41 times greater than that of the neonate, but at 24 h, neonatal peritoneal neutrophils did not reach the adult 4 h level. Peritoneal macrophages increased more rapidly in adults than in neonates. After i.p. infection, adults and neonates developed bacteremia, but adults cleared the bacteria with greater efficiency. Adult blood neutrophils increased 247% by 12 h and then decreased; neonatal neutrophils steadily decreased to a 57% reduction by 24 h. The neonatal neutrophil response to group B Streptococcus, type Ia, infection is inadequate and may contribute to the high mortality associated with this infection.