Seven-day administration of recombinant human granulocyte colony- stimulating factor to newborn rats: modulation of neonatal neutrophilia, myelopoiesis, and group B Streptococcus sepsis

Single-pulse administration of rhG-colony-stimulating factor (CSF) to neonatal rats was previously demonstrated to induce peripheral neutrophilia and modulate bone marrow (BM) neutrophil storage and proliferative pools (NSP + NPP). In this study, we investigated the prolonged effects of 7 days of rhG-CSF therapy (5 micrograms/kg/per day). Sprague-Dawley newborn rats (less than or equal to 24 hours) were injected intraperitoneally (IP) (daily for 7 days) with rhG-CSF or phosphate-buffered saline/human serum albumin (PBS/HSA). RhG-CSF induced a significant early and late peripheral neutrophilia: 6,905 +/- 1,625 (day 1) and 9,223 +/- 515 microL (day 7) v 1,275 +/- 90/microL (P less than or equal to .0001). In addition, 7 days of rhG-CSF resulted in a significant increase in the BM NSP: 3,247 +/- 190/microL v 1,677 +/- 339/microL (P less than or equal to .001). There was, however, no depletion or significant change in the BM NPP. Seven days of rhG-CSF also induced a mild increase in BM CFU-GM colony formation (P less than or equal to .01). There was, however, no significant change in liver/spleen CFU-GM colonies or in the CFU-GM proliferative rate in either the BM or liver/spleen cultures. Finally, 7 days of prophylactic rhG-CSF therapy resulted in a synergistic response with antibiotic therapy and significantly modulated the mortality rate during experimental group B streptococcal sepsis (GBS) (100% v 50%) (GvsC) (P less than or equal to .001). Pulse rhG-CSF administered at 6 hours or 18 hours after GBS inoculation, however, failed to act synergistically with antibiotics to improve survival or prevent peripheral neutropenia. This study suggests that 7 days of prophylactic rhG-CSF therapy induces peripheral neutrophilia, myeloid maturation, increases neutrophil BM reserves and also may provide immunologic enhancement of neonatal host defense during experimental GBS in term neonatal rats.