INFLUENCE OF THE HOST AND PARASITE STRAIN IN A MOUSE MODEL OF VISCERAL LEISHMANIA-INFANTUM INFECTION

We investigated the respective roles of the host and parasite strain i n a murine model of visceral leishmaniasis. Balb/c and C57B1/6 mice we re selected for their respective 'non cure' and 'cure' haplotypes vis- a-vis Leishmania major. Mice were infected with 10(7) stationary-phase promastigotes of four strains of Leishmania infantum with different i nfection profiles in mice: visceralization or regulation, as establish ed by Sulahian et al. (Sulahian et al. (1998) FEMS Immunol. Med. Micro biol. 17, 131-138). The infection was monitored by measuring parasite load in the liver and spleen on days 9, 22, 44 and 57 post-infection, using a sensitive microtitration technique. Similar profiles (visceral izing or regulating) were observed in the two mouse strains, suggestin g a predominant role of the Leishmania strain in the visceralization p rocess. The host response was assessed by analyzing the granulomatous response in the liver and by quantifying specific IgG, IgG1 and IgG2a as a marker of the Th1/Th2 immune response. A granulomatous response w as observed in both strains of mice but was more pronounced with visce ralizing strains of L. infantum and in C57B1/6 mice compared to Balb/c mice. The kinetics of anti-leishmania IgG antibody production was sim ilar in all the groups, but the distribution of IgG1 and IgG2a isotype s was different between the two mouse strains: Balb/c mice had a predo minantly Th2-like response whereas C57B1/6 had a mixed Th1/Th2-like re sponse. This study demonstrates the determining role of both the paras ite and mouse strain in the outcome of L. infantum infection. The Th1/ Th2 concept does not seem to explain susceptibility and resistance to infection in our model of visceral L. infantum infection, contrary to the L. major model. (C) 1998 Published by Elsevier Science B.V. All ri ghts reserved.