Enhancement of protection against Salmonella infection in mice mediated by a synthetic lipopeptide analogue of bacterial lipoprotein in S. typhimurium vaccines.

Vaccines consisting of acetone-killed Salmonella typhimurium were supplemented with a synthetically prepared lipopeptide derivative of bacterial lipoprotein, Pam3Cys-Ser-Ser-Asn-Ala. NMRI mice were immunized with these vaccines, receiving two intraperitoneal injections and were challenged intraperitoneally with graded doses of S. typhimurium C5. The protective capacity of the supplemented vaccines was compared with that of the unsupplemented bacterial vaccine, and with the effectiveness of the supplementing component alone. The LD50 served as a criterion for protective capacity. The results showed that 90% of the S. typhimurium S-form vaccine could be replaced by the adjuvant lipopeptide without a recognizable decrease in protective immunizing capacity. A similar but less pronounced enhancement of protection was obtained with a R-mutant vaccine supplemented with the lipopeptide; by supplementing the standard vaccine dose with lipopeptide an increase in protection was also achieved. Lipopeptide alone was not effective in protecting mice from infection with S. typhimurium.