Protective role for interleukin-5 during chronic Toxoplasma gondii infection

To investigate the role of interleukin-5 (IL-5) during Toxoplasma gondii in fection, IL-5 knockout (KO) mice and C57BL/6 control mice were infected int raperitoneally with ME49 cysts and the course of infection was monitored. T he mortality rate during chronic infection was significantly greater in IL- 5-deficient animals, and consistent with this finding, the KO mice harbored a greater number of brain cysts and tachyzoites than did their wild-type c ounterparts. Although the IL-5 KO animals did not succumb until late during infection, increased susceptibility, as measured by accelerated weight los s, was detectable during the acute stages of infection. The amounts of tota l immunoglobulin (Ig), IgM, and IgG2b were comparable in both strains, whil e the amount of IgG1 was much smaller in IL-5 KO mice. Spleen cell producti on of IL-12 in response to T. gondii antigen was approximately threefold lo wer in the KO strain, and this decrease correlated with a selective loss of B lymphocytes during culture. A link between the presence of B cells and a ugmented IL-12 production was established by the finding that after removal of B cells with monoclonal antibody and complement, wild-type- and KO-deri ved cells produced equivalent levels of IL-12 in response to T,gondii antig en. These results demonstrate a protective role of IL-5 against T. gondii i nfection and suggest that IL-5 may play a role in the production of IL-12.