Cellular Immunity to Leishmania donovani in Macrophages in Culture

Abstract

Macrophages from superinfected mice show a resistance to intracellular forms of L. donovani in culture. The mice were given 2 to 4 intraperitoneal injections of live parasites at 20to 30-day intervals. Peritoneal macrophages from the superinfected and normal control mice were cultured in Leighton tubes. After inoculation with LD bodies of L. donovani, cover slips were removed at intervals to determine the number of intracellular parasites present. In macrophages from normal mice the parasites usually multiplied for the first 72 hr, but in macrophages from superinfected hosts the parasites either failed to multiply or decreased in numbers. When serum from superinfected mice was added to the culture, there was no significant change in either the rate of parasite multiplication in macrophages from normal mice nor in the rate of destruction in cells from infected mice. Resistance was associated with the cells from the superinfected host. There was no evidence that serum antibodies participated in this cultural demonstration of cellular immunity. Cellular immunity to Leishmania seemed to resemble the cellular immunity described as a factor of resistance to several other microorganisms which parasitize macrophages, such as Toxoplasma, Salmonella, and tubercle bacilli. Although humans and animals have a long lasting resistance to reinfection after recovery from most forms of leishmaniasis, the nature of the immunity is not known. Stauber (1963) stated, concerning humoral aspects of resistance, there is yet no evidence for an antibody basis of acquired resistance to either dermal or visceral Serological tests that have been employed to date are neither highly specific nor do they demonstrate protective antibodies. Adler (1963, 1964), Manson-Bahr (1963), and Stauber (1963) have summarized our limited knowledge of immunity to leishmaniasis. In recent years only limited attempts have been made to demonstrate cell associated systems of resistance. Adler and Nelken (1965) failed to transfer the delayed hypersensitivity reaction by injecting washed leukocytes from the blood of one hypersensitive donor into norisensitive human recipients. Bray and Lainson (1965) were unsuccessful in similar experiments on humans, monkeys, rabbits, and guinea pigs. More recently, Boysia (1967) was able Received for publication 14 May 1968. * This investigation was supported in part by Contract DADA17-67 C-7142 from the U. S. Army Medical Research and Development Command, by Public Health Service Fellowship 1-F1-GM34,783 from the National Institute of General Medical Sciences and by the Michigan State University Agriculture Experiment Station. Michigan Agriculture Experiment Station Journal Article No. 4398. t transfer passively the delayed hypersensitivity reaction using lymph node cells from sensiized guinea pigs. None of these authors tested the resistance of the recipients to infection. Cellular immunity has been demonstrated to be an important factor in the host's resistance to a number of intracellular parasites including: Mycobacterium, Salmonella, Brucella, Listeria, and Toxoplasma. All of these organisms are known to be intracellular parasites of macrophages. It is this host cell which expresses the resistance to the parasite that has been termed cellular immunity. The subject has been reviewed by Suter and Ramseier (1964) and Shands (1967). Since Leishmania has a predilection for macrophages, it seemed promising to determine what role cellular immunity plays in the host immunity to leishmaniasis. MATERIALS AND METHODS