The cellular response to Listeria monocytogenes is mediated by a heterogeneous population of immunospecific T cells.

Immunospecific T cells cooperate with macrophages in the expression of delayed type hypersensitivity and cellular resistance to Listeria monocytogenes. The mediator cells involved are generated in response to an immunizing Listeria infection. Immunospecific T cells are formed in lymphoid tissue and appear briefly in the blood. Many localize at sites of microbial implantation, but others leave the blood spontaneously and infiltrate tissues throughout the body. Both circulating T cells and those in tissues participate in the expression of delayed type hypersensitivity and cellular resistance. Several lines of evidence suggest that these two phenomena are mediated by heterogeneous but possibly cooperating T cell populations.