Characterization of the cell-mediated immune response to Listeria monocytogenes in the murine BALB/c model

Abstract

This research was designed to characterize the in vivo and in vitro immune responsiveness of the BALB/c strain of mice to the facultative intracellular parasite Listeria monocytogenes. It was found in this model system that protective immunity developed concomitantly with delay-type hypersensitivity but that expression of the former disappeared after fifty-five days while the latter persisted. Spleen cells from animals demonstrating solid immunity to the organism were cultured in vitro for production of macrophage activation factor (MAF) and macrophage migration inhibitory factor (MIF). Analyses of the in vitro system demonstrated that seventy-two hours were necessary for maximal MAF and MIF activities. Maximum expression of MAF in peritoneal macrophage required only twenty-four hours of incubation prior to infection with L. monocytogenes and penicillin at 1.0 unit/ml was necessary in the assay system. Fresh cultures of macrophage were necessary for expression of MAF activity as all activity was lost after five days of culture in vitro prior to activation. Preliminary characterization of the two activities yielded results which were similar for both. MAF activity was expressed at dilutions of at least 1:32 while MIF activity was demonstrable at a 1:16 dilution. Both activities were stable at 56*C but lost potency when this temperature was exceeded. Sequential precipitation with ammonium sulfate yielded heterogeneous fractions in which MAF activity was recovered in the 40-60% saturation range while MIF activity was spread throughout all fractions. Sephadex G-150 column profiles yielded MAF and MIF activities corresponding to proteins of a molecular weight range of 25,000 to 45,000 daltons. Polyacrylamide gel electrophoresis and immunoelectrophoresis experiments suggested an association of activities in fractions containing albumin but were ineffective in delineating active and inactive proteins.