Factors influencing the host response to Leishmania mexicana

The immune response of resistant and susceptible mice infected with Leishmania mexicana has been studied. In resistant mice infection was associated with the development of delayed hypersensitivity to parasite antigens and the development of specific antibodies, and protective immunity to a subsequent challenge infection with L. mexicana was demonstrable. After adoptive transfer of lymph node cells and peritoneal cells from immune donors, recipient mice showed an increased ability to control a challenge infection. T lymphocytes from recovering mice, transferred together with parasite antigens, mediated a specific delayed hypersensitivity. In a local cell-transfer assay, peritoneal cells from immune mice produced significant protection against a living inoculum. Immune serum enhanced the protection conferred by peritoneal cells, but immune serum alone was ineffective. It is postulated that immunity to L. mexicana is mediated by collaboration between T-cell activated macrophages and antibodies. In susceptible BALB/c mice, infection with L. mexicana led to the activation of specific and non-specific suppressor cells. The former are related to T cells whereas the latter belong to the splenic population of adherent cells. Non-specific suppression by these adherent cells was at least partially associated with the release of a suppressor factor that could inhibit the blastogenic response of normal spleen cells activated by mitogens. Both in vitro and in vivo studies suggested the participation of a high parasite load in the induction of non-specific suppressor cells and polyclonal lymphocyte activation.