THE ADMINISTRATION OF COMPLEMENT COMPONENT C9 ENHANCES THE SURVIVAL OF NEONATAL RATS WITH ESCHERICHIA-COLI SEPSIS

To determine the significance of neonatal C9 deficiency, an animal mod el was developed in the rat. By rocket immunoelectrophoresis, the conc entration of C9 in pooled adult rat serum was 224 +/- 7.2 mu g/mL. In contrast, the concentration of C9 in pooled serum from 1-d-old rats wa s only 43 +/- 3.8 mu g/mL and increased during the first 3 wk of life to 170 +/- 20 mu g/mL. Similarly, the capacities of neonatal rat serum to kill two pathogenic strains of Escherichia coli and to lyse sensit ized sheep erythrocytes were diminished compared with adult serum but increased during the first 3 wk of life. Supplemental human C9 signifi cantly enhanced the bactericidal and hemolytic activity of neonatal ra t serum. The capacity of neonatal rats to survive after the intrapulmo nary injection of E. coli was positively correlated with the serum C9 concentration, bactericidal activity, and hemolytic activity. In 2-d-o ld rats infected with E. coli, the intraperitoneal administration of h uman C9 significantly enhanced survival and also enhanced the protecti ve effect of intraperitoneal human IgG antibodies. The data indicate t hat C9 deficiency predisposed neonatal rats to invasion by E. coli. Th e neonatal rat appears to be a suitable model with which to investigat e the significance of C9 deficiency.