Acquired resistance to facultative intracellular bacteria: relationship between persistence, cross-reactivity at the T-cell level, and capacity to stimulate cellular immunity of different Listeria strains

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Abstract
C57BL/6 mice were infected with different strains of Listeria sp., and bacterial survival in spleens was assessed. Six strains (EGD, NCTC 5348, ATCC 19113, ATCC 19114, NCTC 10527, and ATCC 19116) were able to persist in spleens (persistent strains), whereas with five other strains (ATCC 19111, ATCC 19119, ATCC 33090, ATCC 33091, and ATCC 14870), only few if any bacteria were demonstrable after infection with up to 10(8) organisms (nonpersistent strains). Immunization of mice with persistent listeriae induced strong immune responses as determined in vitro (antigen-induced proliferation and interleukin production) and in vivo (protection and delayed-type hypersensitivity), whereas immunization with nonpersistent bacteria resulted in weaker responses. On the other hand, T lymphocytes from mice immunized with live organisms of the persistent strain EGD were stimulated equally well by heat-killed listeriae of all strains. Furthermore, three T-cell clones which were able to adoptively mediate antibacterial protection in vivo could be stimulated by heat-killed organisms of persistent as well as nonpersistent Listeria strains. It is concluded that both persistent and nonpersistent listeriae express antigenic epitopes which are recognized by protective T cells, although nonpersistent strains are not effective in inducing cellular immune responses due to rapid elimination in the host.