Abstract
Susceptibility of mice to infection with Yersinia enterocolitica has been shown to be related to neither the Ity locus encoding for resistance to Salmonella typhimurium and other pathogens nor the H-2 locus. Recent studies in our laboratory have demonstrated that T-cell-mediated immune responses are required for overcoming primary Yersinia infection. In the present study, we investigated the course of infection with Y. enterocolitica and the resulting immune responses in Yersinia-susceptible BALB/c and Yersinia-resistant C57BL/6 mice. In the early phase of infection, the clearance of the pathogen was comparable in both strains of mice, suggesting similar mechanisms of innate resistance. Splenic T cells from Yersinia-infected C57BL/6 mice exhibited marked proliferative responses and produced gamma interferon (IFN-gamma) upon exposure to heat-killed yersiniae. By contrast, the Yersinia-specific T-cell response in BALB/c mice was weak, and IFN-gamma production could not be detected before day 21 postinfection. T cells isolated from C57BL/6 mice 7 days after infection mediated immunity to Y. enterocolitica but those from BALB/c mice did not, while at 21 days postinfection T cells from both strains mediated protection. Neutralization of IFN-gamma abrogated resistance to yersiniae in C57BL/6 mice but to a far smaller extent in BALB/c mice. Administration of recombinant IFN-gamma or anti-interleukin-4 antibodies rendered BALB/c mice resistant to yersiniae, whereas this treatment did not significantly affect the course of the infection in C57BL/6 mice. These results indicate that the cellular immune response, in particular the production of IFN-gamma by Yersinia-specific T cells, is associated with resistance of mice to Y. enterocolitica.