Importance of lymphokines in the control of multiplication and dispersion of Leishmania donovani within liver macrophages of resistant and susceptible mice.

Leishmania donovani is an obligate intracellular parasite of mammalian macrophages. The immunosuppressant cyclosporin A (CsA), which inhibits the production of interleukin (IL)-1, IL-2, and interferongamma, increased infections 3-fold without affecting expression of the Lsh gene. The objective of this study was to determine how activation of macrophages by lymphokines affects the multiplication and propagation of the parasite within liver macrophages. Susceptible C57BL/6J and resistant C57L/J mice were treated with 200 mg/ kg CsA and then infected intravenously with 107 amastigotes. Two weeks later macrophages were collected from the liver by perfusion, plated on coverslips, and incubated for 4, 24, and 48 hr. The percentage of infected macrophages and the number of amastigotes/100 cells were determined after staining the cells with Giemsa's stain. The number of infected macrophages and amastigotes per macrophage was significantly greater in animals of both strains that had been treated with CsA. This study demonstrated clearly that lymphokines or other soluble mediators produced by T cells act, in part, to control infection by L. donovani by minimizing both multiplication within macrophages and their dispersion. When infected with Leishmania donovani, some inbred strains of mice demonstrate a greater multiplication of the parasite within liver and spleen macrophages; others show less multiplication of the organism (Bradley, 1977). Innate resistance to this intracellular parasite is controlled by a single gene (Lsh), which maps on chromosome 1 (Bradley et al., 1979). Many in vivo studies have demonstrated that T cells are ineffective in regulating the expression of this gene, which also controls infection by other intracellular pathogens (Bradley and Kirkley, 1972; O'Brien and Metcalf, 1982; Skamene et al., 1982; Hoermache et al., 1983; Ulczak and Blackwell, 1983). Whereas T lymphocytes have not shown any regulating effect on the expression of the Lsh gene, the importance of T cells in the elimination of Leishmania donovani in C57BL/6J mice has been well demonstrated by Skov and Twohy (1974). Recently, Reiner and Finke (1983) and Reiner (1987) showed that the production of inReceived 18 August 1988; revised 4 May 1989; accepted 6 June 1989. * Present address and author to whom correspondence should be addressed: University of British Columbia, Department of Medicine, Division of Infectious Diseases, G. F. Strong Research Laboratory, Vancouver General Hospital, 2733 Heather Street, Vancouver, British Columbia, Canada V5Z 1M9. terleukin (IL)-1 and IL-2 by BALB/c cells is inhibited during infection in vitro and in vivo, and Murray et al. (1987) reported that the infection reduces the capacity of animals to produce interferon (IFN)-gamma. These findings demonstrate clearly that the infection suppresses several immunological functions of the host, permitting the establishment of the parasite. Murray et al. (1982) have also shown that the level of parasitism seems to be inversely related to the ability of the organism to stimulate the production of macrophage-activating lymphokines by T cells. Suppression by the immunosuppressive drug cyclosporin A (CsA) of T helper cell function and the secretion of IL1 by macrophages permits a highly significant increase in the parasite load of infected animals (Olivier and Tanner, 1989). It was, thus, of interest to determine the effect of the drug at the macrophage level, because, in CsA-treated mice, the production of macrophage-activating lymphokines is inhibited (Olivier and Tanner, 1989). That study also showed the level at which lymphokines affect the establishment of the parasite during the first (innate) phase of the infection and the importance of T helper cell populations in controlling L. donovani. In that study an increase of the level of infection in resistant and susceptible strains of mice was clearly observed. In this study we sought to determine if this was due to greater multipli-