Immunomodulation by surface components of Listeria monocytogenes: a review.

Surface components of bacteria make the initial contact with host defence mechanisms. Such components from Listeria monocytogenes have been studied in attempts to elucidate mechanisms of pathogenicity. The cell walls of different serotypes of L. monocytogenes have been reported to contain abundant peptidoglycan, teichoic acid, lipoteichoic acid, endotoxin, and lipopeptidopolysaccharide. Cell walls are B cell mitogens in vivo and in vitro, fix complement, are chemotaxigenic and decrease resistance to infection with Listeria. A soluble, high molecular weight immunosuppressive agent is also a B cell mitogen in vitro. It induces an inflammatory response and a population of suppressor macrophages in vivo. Monocytosis-producing activity is a low molecular weight material associated with the cell membrane. It induces a labile, transient endogenous mediator and causes a 3-6 fold elevation in blood monocyte levels 48 h after injection. Mice genetically sensitive to Listeria infection fail to produce or respond to the endogenous monocytosis-inducing factor. The potential use of these factors in diagnosis of Listeria and in unravelling interrelationships in host defense mechanisms is discussed.