Suppression of resistance to Giardia muris and cytokine production in a murine model of acquired immune deficiency syndrome

Peyer's patch (PP) T cells through the production of appropriate cytokines foster the development of immunity to the intestinal protozoan parasites such as Giardia. T cell destruction by the human immunodeficiency virus precedes the development of acquired immune deficiency syndrome. Thus, HIV may increase susceptibility to intestinal parasite infections. Therefore, we measured the resistance and T cell cytokine responses to Giardia in C57Bl/6 mice infected with the retrovirus LP-BM5 which produces a murine AIDS (MAIDS). Mice with MAIDS and controls were intragastrically challenged with 1 x 10⁵ G. muris cysts. Fecal counts were measured weekly following challenge. Also, PP T cell production of interleukin (IL)2, IL3, IL4, and Interferon-γ in response to G. muris trophozoite antigens displayed on antigen presenting cells were measured at these times. Prior to day 14 of the infection, the number of Giardia cysts in the retrovirus group paralleled that in controls. However, by day 21 after Giardia infection, mice with MAIDS failed to clear the Giardia cysts from the intestine while the control mice were completely free of cysts. IL2 and IL4 production in response to Giardia trophozoites by unfractionated PP lymphocytes were severely depressed in the retrovirus infected group, while IFN-γ production was increased. Depressed cytokine production was most likely due to depressed PP T cell numbers. When fractionated enriched T cells were adjusted to a uniform concentration in in vitro immunization cultures, the production of IL2 and IL4/IL5 were similar between retrovirus infected compared with control mice. Recoverable PP T cells were lower in mice with MAIDS. These data suggest that the production of key PP T cell cytokines, IL2 and IL4, which foster the development of appropriate mucosal immunity are severely depressed following infection with the murine retrovirus LP-BM5. This immunodeficiency leads to a failure to clear the intestinal protozoan parasite Giardia muris.