Failure of FIV-infected cats to control Toxoplasma gondii correlates with reduced IL2, IL6, and IL12 and elevated IL10 expression by lymph node T cells

Increased susceptibility to intracellular pathogens in HIV-infected individuals and FIV-infected cats is attributed to a defective T-helper 1 (Th1) immune response. However, little is known about specific cytokine responses to secondary pathogens. To address this question, control and FIV-infected cats were challenged with Toxoplasma gondii, and lymph node cells analyzed for cytokine mRNA expression. Twenty-four weeks post-FIV infection, prior to T. gondii challenge, IL2 and IL12 mRNAs were depressed, whereas IL10 and IFNγ mRNAs were increased in CD4+ and CD8+ subsets. Following T. gondii challenge, control cats showed increased expression of IL2, IFNγ, IL10, IL12, and IL6 mRNAs. In contrast, IL2, IL6, IFNγ, and IL12 mRNAs were suppressed in FIV–T. gondii co-infected cats, whereas IL10 remained at the high prechallenge levels. IFNγ and IL10 mRNAs were produced by both CD4+ and CD8+ cells in FIV–T. gondii cats. Elevated IL10 may suppress a Th1 cytokine response to T. gondii challenge.