Selective activation and expansion of high-affinity CD4+ T cells in resistant mice upon infection with Leishmania major.

Using multimers of MHC class II molecules linked to a peptide derived from the Leishmania LACK antigen, we have compared the fate of parasite-specific CD4+ T cells in resistant and susceptible mice transgenic for the beta chain of a LACK-specific TCR. Activated T cells were readily detected in the draining lymph nodes of infected animals. Although the kinetics of activation and expansion were similar in both strains, T cells from susceptible and resistant mice expressed low- and high-affinity TCR, respectively. As T cells from resistant mice produced more IFN-gamma and less IL-4 than those from susceptible animals, our results suggest that differences in TCR usage between MHC-matched animals may influence the development of the antiparasite immune response.