Protective mechanisms against infection by Listeria monocytogenes: accumulation and activation of macrophages.

The protective mechanisms against Listeria monocytogenes were analysed in mice. Listeria immune mice were rechallenged with viable listeria, and the degree of activation of macrophages, the degree of accumulation of macrophages to the infected sites, and these mechanisms were studied. Enhanced acquired resistance to the reinfection became detectable from the early stage of immunization. It was observed that activation of macrophages was mediated by pretreatment with antigen from the early stage of immunization. Enhanced accumulation of macrophages at the infected sites was observed only in the early stage. Enhanced accumulation and activation of macrophages in the early stage were generated by mediators from listeria antigen sensitized T lymphocytes which were different from classical tuberculin type. Enhanced activation of macrophages in the later stage was generated by MAF and/or MIF from sensitized T lymphocytes of classical tuberculin type. It was suggested that acquired cellular resistance to listeria in the early stage depends on both activation and accumulation of macrophages, and that in the later stage depends on activation of macrophages.