Intestinal infection of BALB/c mice with Yersinia enterocolitica O9 causesmajor modifications in phenotype and functions of spleen cells

Yersinia enterocolitica serotype O9 may cause a persistent intestinal infec tion with few or no symptoms in humans and in BALB/c mice. The present stud y demonstrated profound alterations in the immune status of BALB/c mice inf ected with Y. enterocolitica O9. Infected mice developed splenomegaly and p henotypic analysis of spleen cells revealed increases in CD3(+) total T cel ls, CD4(+) helper T cells, CD8(+) cytotoxic T cells and CD11b(+) phagocytic cells. Spleen cells from infected mice exhibited impaired responses to mit ogens and suppressed the proliferation of normal splenocytes in response to mitogens. Suppression of responses to concanavalin A and heat-killed yersi niae was associated with increased production of gamma interferon and react ive nitrogen intermediates. Y. enterocolitica-infected mice resisted challe nge with a lethal dose of the intracellular pathogen Listeria monocytogenes . These findings suggest that infection of mice with Y. enterocolitica O9 i nduces gamma-interferon-secreting cells that promote macrophage activation, mediating resistance to infection with L. monocytogenes, and macrophage pr oduction of reactive nitrogen intermediates, which results in in vitro inhi bition of lymphocyte response to mitogens.