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In this study we analyzed the influence of cyclosporin A (CyA) on the process of phagocytosis of L. major promastigotes and amastigotes by inflammatory peritoneal macrophages (MP) from BALB/c mice. Our data clearly demonstrate that CyA profoundly enhanced the degradation by peritoneal MP of both intracellular L. major promastigotes and amastigotes. This effect was T cell-independent and specifically associated with CyA, since the similarly structured cyclosporin F (CyF) was ineffective. CyA did not alter the replication and infectivity of extracellular parasites. From these results we conclude that the inhibition of intracellular parasite replication in the presence of CyA substantially contributes to the previously described suppressive effect of CyA on the development of L. major-induced lesions in BALB/c mice.

Destruction of intracellularly living Leishmania major amastigotes is achieved by activated macrophages. In this report, we have investigated the contribution of IL-4, TNF-alpha and IFN-gamma to the induction of antileishmanial macrophage activation. It was found that as single lymphokine only IFN-gamma led to amastigote elimination by peritoneal exudate macrophages. Neither IL-4 nor TNF-alpha or the combination of both cytokines led to antimicrobial activation. When the macrophages were incubated with concentrations of IFN-gamma that by themselves were insufficient for maximum cell activation, it was found that both IL-4 and TNF-alpha very effectively synergized with IFN-gamma for induction of antiparasitic activity. The activation which was achieved when IFN-gamma was combined with IL-4 could be blocked not only with antibodies to either of the lymphokines, but also with an antiserum specific for TNF-alpha, suggesting the involvement of endogenously generated TNF-alpha in this synergism. Any of the synergistic activities observed presumably lead to the activation of the L-arginine dependent pathway used by the cell for the production of nitrogen oxides as effector molecules for parasite killing since NG-monomethyl-L-arginine (L-NMMA), a specific inhibitor of this pathway, completely blocked the killing of intracellular parasites. We conclude that macrophage activation for antiparasitic activity is directed by a complex network of cytokine-interactions, in which IL-4 and TNF-alpha very effectively synergize positively with low levels of IFN-gamma.

The influence of niridazole, an anti-helminthic drug, on cell-mediated immune responses was investigated. Allograft rejection in mice as well as the in vitro induction of cytotoxic T lymphocytes (CTL) against murine alloantigen were used as the test system. Repeated daily oral treatment of host mice with niridazole (100 mg/kg) prior to and during allotransplantation resulte in the postponement of graft rejection, inducing a transitory functional state of allograft tolerance. The time interval between the termination of niridazole administration and onset of graft rejection was estimated to be 5-7 days. In order to test the effect of niridazole or its derivatives on the in vitro induction of alloreactive CTL, the serum or urine of mice which were treated with niridazole were added to the cultures, instead of adding niridazole directly to the cultures. Such serum and urine were found to be inhibitory for in vitro induction of CTL. The serum and urine had no effect on the effector phase of CTL.