Neutrophil mobilization induced by complement fragments during experimental group B streptococcal (GBS) infection

Degradation products of the third component of complement have been reported to have the ability to mobilize leukocytes from the marrow and induce leukocytosis. The effect of C3d,g preparations on neutrophil responses in a neonatal rat model of group B streptococcal infection in which neutrophil mobilization from the marrow is inadequate has been evaluated. Dimeric and monomeric fragments of C3d,g were isolated from human serum; the identity of the C3d,g preparations was confirmed by SDS-PAGE, Western blotting, and N-terminal amino acid sequencing. Uninfected neonatal rats responded to intraperitoneal injection of C3d,g with a peripheral blood neutrophilia at 30 minutes and 4 hours after inoculation. C3d,g, which lacks intrinsic chemotactic activity, enhanced the local accumulation of neutrophils in the peritoneal cavity of infected, but not uninfected, neonatal rats. In addition, myeloid cell release from the marrow of isolated femurs of neonatal rats receiving C3d,g was significantly enhanced. Thus, the effect of C3d,g in this model was to mobilize marrow cells and induce peripheral leukocytosis. Chemotactic factors released at the site of infection then resulted in the local accumulation of these inflammatory cells. Complement-derived components capable of releasing marrow myeloid elements may play a major role in determining the outcome of bacterial infection in the immature host.