Abstract
Protection against experimental Serratia marcescens infection in mice was enhanced by prior injection of formalin-killed or viable bacteria of the same strain. From the first to the fourth week after vaccination, specific immunity was involved in the host defence against systemic serratia infection. The transfer of antiserum specific for S. marcescens increased bacterial clearance from the liver, but did not increase the survival of the mice. Bacterial clearance from the liver was also increased by the transfer of spleen cells from immunised mice, but, again, survival was not increased. However, the transfer of both antiserum and spleen cells from vaccinated mice increased both bacterial clearance from the liver and survival (p less than 0.01). These results suggest an additive effect of humoral immunity and T-cell-mediated immunity in protection against systemic serratia infection.