The role of antibody in the interaction of Salmonella and listeria with peritoneal macrophages.

That in vitro killing by normal and activated macrophages of S. typhimurium and other gram-negative organisms is dependent on the presence of antibody has been confirmed. It has been shown that antibody is required for the binding of S. typhimurium to the surfaces of macrophages. This binding can be inhibited by the Fc portion of immunoglobulin, indicating that the Fc receptors on macrophages are used for binding S. typhimurium. It has also been confirmed that antibody does not appear to be necessary for killing of L. monocytogenes to occur. The organisms bind to the surface of macrophages by different receptors. Binding of L. monocytogenes occurs in the absence of added antibody and Fc fragments of immunoglobulin do not affect the binding. Attachment can be inhibited, however, by removal of divalent cations, a treatment that has no effect on antibody-mediated binding as, under these conditions, the binding of L. monocytogenes to macrophages can be enhanced by antibody. The significance of these findings is discussed.