Analysis of the role of natural killer cells in Listeria monocytogenes infection: Relation between natural killer cells and T-cell receptor γδ T cells in the host defence mechanism at the early stage of infection

We have reported that T cells bearing T-cell receptors (TcR) of γδ type (γδ T cells) appear in the peritoneal cavity in a relatively early stage of primary intraperitoneal (i.p.) Listeria monocytogenes infection, and play a significant role against the infection. To elucidate the protective role of natural killer cells which also appear in the early stage of L. monocytogenes infection, mice were treated with anti-NK1.1 monoclonal antibody (mAb) to deplete NK cells before the infection. They exhibited accelerated clearance of L. monocytogenes, accompanied by enhanced induction of γδ T cells in the peritoneal cavity compared with non-treated mice. When the mice were depicted of γδ T cells by in vivo administration of anti-TcR γδ mAb, the bacterial burdens of organs from infected mice were not affected by NK cell depletion. These results suggest that, although NK cells increase significantly during the early stage of L. monocytogenes infection, they do not take part in the early host resistance against i.p. L. monocytogenes infection. It is also suggested that increased γδ T cells in the peritoneal cavity of NK cell- depleted mice can be one of the factors responsible for the enhanced clearance of L. monocytogenes in the early stage of infection.