The synergistic contribution of macrophages and antibody to protection against Salmonella typhimurium during the early phase of infection.

The contribution of phagocytes and antibody to protection against Salmonella typhimurium during the early phase of infection in mice was analysed. Following intravenous injection, most of the bacteria were trapped in the liver and spleen within 10 to 60 min and killed within 6 h; surviving organisms began to multiply in these tissues after 24 h and reached a maximum at 5 to 7 d. The transient killing phase was abrogated by treatment with carrageenan, a macrophage blocker, but not by whole-body X-irradiation. These observations suggest that carrageenan-sensitive, but radio-resistant macrophages play an important role in the early phase of the infection. Actively immunized mice showed accelerated trapping and killing; the protection observed at the early stage of infection in immunized mice could be passively transferred to normal mice, whereas carrageenan-treated mice did not kill the bacterial even after receiving immune serum. It seems that the synergistic action of macrophages and antibody provided the main initial primary defence in immune animals.