Effects of bacterial products on lymphocytes and macrophages: their possible role in natural resistance to Listeria infection in mice

Fluids from Listeria monocytogenes cultures contain products that possess a number of biologic activities. The fluids contain a mitogenic substance for B lymphocytes. Thus, their injection into mice produces striking hyperplasia of the B cell zones of the spleen. Also, lymphocytes in vitro are stimulated to proliferate, regardless of whether they are first depleted of T lymphocytes by exposure to anti theta serum plus complement. These fluids injected intraperitoneally activate macrophages as judged by morphologic criteria. Mice that receive the products develop a transitory state of nonspecific resistance to infection by live Listeria. The relationships between B cell mitogenicity and macrophage activation and protection were not established. This kind of reaction of lymphoid cells to Listeria products may represent an early nonspecific line of defense against bacterial invasion.