Cytokine Production of CD8 + Immune T Cells but Not of CD4 + T Cells from Toxoplasma gondii -Infected Mice Is Polarized to a Type 1 Response Following Stimulation with Tachyzoite-Infected Macrophages

To examine whether cytokine production of CD4⁺immune T cells and CD8⁺immune T cells in Toxoplasma gondii-infected mice differ in their responses to infected cells and to soluble antigens of the parasite, we compared the production of interferon-γ (IFN-γ), interleukin-2 (IL-2), IL-4, and IL-10 by the immune T cell populations following in vitro stimulation with tachyzoite-infected macrophages and tachyzoite lysate antigens(TLA). Both CD4⁺and CD8⁺immune T cells produced large amounts of IFN-γ in response to either infected macrophages or TLA, but the CD4⁺T cells produced greater amounts of the cytokine than did the CD8⁺T cells with both stimulations. Both T cell populations also produced IL-2 after stimulation with infected macrophages, whereas only CD4⁺T cells did when stimulated with TLA. CD4⁺immune T cells also produced large amounts of IL-4 and IL-10 after stimulation with infected macrophages, but CD8⁺T cells did not. These results indicate that CD4⁺immune T cells produce IFN-γ, IL-2, IL-4, and IL-10 in response to infected macrophages, whereas CD8⁺immune T cells produce predominantly IFN-γ and IL-2. Since IL-4 and IL-10 could suppress IFN-γ-mediated protective mechanisms against the parasite, the production of these cytokines by CD4⁺immune T cells in response to infected cells could negatively affect their protective activity in vivo.