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 CD4⁺ 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.