A protective role of extrathymic αβ TcR cells in the liver in primary murine salmonellosis

The liver comprises unique T cells differentiating extrathymically and expressing an intermediate intensity of αβ T-cell receptor (TcR) and a high intensity of leucocyte function antigen-1 (LFA-1). To elucidate the functional roles of the intermediate αβ TcR cells in host defence against bacterial infection, we examined the effects of depletion of the intermediate αβ TcR cells by in vivo administration of monoclonal antibodies (mAb) to intercellular adhesion molecule-1 (ICAM-1). LFA-1 and αβ TcR on the bacterial growth in the liver after infection with Salmonella chorelaesuis in mice. Pretreatment with mAb to LFA-1 (200 μg/mouse) together with mAb to ICAM-1 (200 μg/mouse), which could preferentially deplete the intermediate αβ TcR cells and γδ 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-αβ TcR mAb (60 μg/mouse), which depleted only bright αβ 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 αβ TcR cells by pretreatment with a high dose of anti-αβ TcR mAb (120 μg/mouse) allowed the bacteria to multiply exaggeratedly in the liver at this stage. These results suggest that intermediate αβ 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 αβ TcR in liver at the early stage after Salmonella infection.