INTERACTIONS BETWEEN MURINE AIDS (MAIDS) AND TOXOPLASMOSIS IN CO-INFECTED MICE

We coinfected C57B1/6 mice with LP-BM5 murine leukaemia viruses, respo nsible for murine AIDS (MAIDS), and an avirulent strain of Toxoplasma gondii. Virus-infected mice were infected perorally on day 30 with 10 cysts of T. gondii, and T. gondii-infected mice were challenged with L P-BM5 on day 20, 30 or 60 after parasite inoculation. Uninfected and s ingly infected mice were used as controls. The kinetics of parasite bu rden in blood, lungs and brain, together with blood lymphocyte subsets , and spleen and lymph node weights, were serially determined in each group of mice. The kinetics of parasite counts in mice infected by LP- BM5 then by T. gondii were similar to those in mice infected by T. gon dii only, except for lung counts, which reached higher values than in animals infected with T. gondii alone, then fell and re-increased unti l the end of the experiment. The only significant change in parasite b urdens when mice were first infected by T. gondii and then by LP-BM5, compared with T. gondii controls, was an increase in lung counts in mi ce challenged with LP-BM5 20 days after T. gondii inoculation. Whateve r the schedule of co-infection, the kinetics of lymphocyte subsets in co-infected mice differed from those in T. gondii- or LP-BM5-infected mice; in dually infected mice CD4(+) and CD8(+) cell counts were inter mediate between values in mice singly infected by the parasite or the virus. Enlargement of spleen and lymph nodes, which is a major criteri on of MAIDS progression, was significantly less marked in co-infected mice than in mice infected with LP-BM5 alone. These data point to cros s-regulation of T. gondii and LP-BM5 infections, which results in incr eased susceptibility to T. gondii, and may alter the progression of MA IDS.