Listeria monocytogenes reactive T lymphocytes in healthy individuals.

Peripheral blood mononuclear cells of healthy individuals were enriched for T lymphocytes and stimulated with killed organisms of Listeria sp. Different strains of Listeria sp. induced comparable T cell responses independent from their pathogenicity and virulence. Evidence is presented that killed L. monocytogenes organisms lacked mitogenic activity for human B and T lymphocytes. It is concluded that Listeria reactive T lymphocytes are commonly present in healthy individuals and hence may contribute to the rare occurrence of listeriosis in normal adults.