Variations in susceptibility to Leishmania amazonensis infection in lines of mice selected for high or low immunoresponsiveness

Susceptibility and resistance to Leishmania amazonensis in H-2q syngeneic high and low antibody responder mice (Biozzi mice)

H-2 syngeneic H and L (Biozzi) mice provide a model to study Leishmania infections in which polar resistant and susceptible phenotypes are independent from H-2 differences. High-Ab-responder (H) and low-Ab-responder (L) mice syngeneic at the H-2 locus (H-2q) were, respectively, susceptible and highly resistant to Leishmania amazonensis infection. L-mice resistance was associated with high IFN-gamma and transient IL-4 production by lymph node (LN) cells, in contrast with sustained IL-4 and decreasing IFN-gamma production by susceptible H mice. IL-12 production could be detected only in LN from resistant mice. The cytokine production pattern was consistent with preferential progression to a Th1-type response in resistant L-mice, and to a Th2-type response in susceptible H-mice. We also investigated whether this shift towards Th1- or Th2-type cytokine responses was dependent upon H or L antigen presenting cells' (APC) intrinsic ability to preferentially stimulate either T-cell subset. To this end, LN-derived T-cell lines were grown from 12-day infected mice, when both strains produced IFN-gamma and IL-4. L-derived T-cell lines developed a Th2 cytokine pattern whereas H-derived T-cell lines produced IFN-gamma, IL-4 and IL-10 whatever the APC origin (H or L) used for their derivation. This work constitutes the first characterization of cellular immune responses to the intracellular parasite, L. amazonensis in H-2 syngeneic mice, an infection model in which polar resistant and susceptible phenotypes are determined by non-MHC genes.