Cross-reactions in cell-mediated immunity to Salmonella causing enteric fever.

Cross-reactivity in a delayed-type hypersensitivity (DH) response was studied in mice immunised with live Salmonella typhi, S. paratyphi A and S. paratyphi B. Extensive cross-reactions outside the serogroup limits were observed. The ability of DH cross-reacting and non-cross-reacting sonicates to generate activated macrophages was studied in mice immunised 3 months earlier with S. paratyphi B. Whereas DH cross-reacting S. poona sonicate generated activated macrophages the non-cross-reacting S. typhi sonicate did not. To determine whether infections due to diarrhoea-causing salmonellae generated cross-reactive cell-mediated immune responses against enteric fever-causing organisms, similar reverse experiments were performed in mice immunised with S. enteritidis. S. paratyphi A sonicate generated both effector responses, i.e., DH and activated macrophages.