A protective role of extrathymic alpha beta TcR cells in the liver in primary murine salmonellosis.

The liver comprises unique T cells differentiating extrathymically and expressing an intermediate intensity of alpha beta T-cell receptor (TcR) and a high intensity of leucocyte function antigen-1 (LFA-1). To elucidate the functional roles of the intermediate alpha beta TcR cells in host defence against bacterial infection, we examined the effects of depletion of the intermediate alpha beta TcR cells by in vivo administration of monoclonal antibodies (mAb) to intercellular adhesion molecule-1 (ICAM-1)/LFA-1 and alpha beta TcR on the bacterial growth in the liver after infection with Salmonella chorelaesuis in mice. Pretreatment with mAb to LFA-1 (200 micrograms/mouse) together with mAb to ICAM-1 (200 micrograms/mouse), which could preferentially deplete the intermediate alpha beta TcR cells and gamma delta TcR cells in the liver, resulted in a severely reduced ability to resolve acute phase of Salmonella infection in the liver. Pretreatment with a low dose of anti-alpha beta TcR mAb (60 micrograms/mouse), which depleted only bright alpha beta TcR cells, did not affect the bacterial growth in the liver at the early stage after Salmonella infection, while the depleting of both intermediate and bright alpha beta TcR cells by pretreatment with a high dose of anti-alpha beta TcR mAb (120 micrograms/mouse) allowed the bacteria to multiply exaggeratedly in the liver at this stage. These results suggest that intermediate alpha beta TcR cells may play an important role in protection at the early stage after Salmonella infection in liver and that the interaction of ICAM-1/LFA-1 is critically involved in protective roles of extrathymic T cells bearing intermediate alpha beta TcR in liver at the early stage after Salmonella infection.