IL17A and parasitic infectious disease: By day 6 p.i., IL-12p40 (Fig. 5D) and IL-9 (Fig. 6C) levels were significantly elevated above those of controls and continued to rise through day 10 p.i. Increasing levels of IL-10 and IL-12p40, an antagonist of IL-12, likely blunt the Th1 response, perhaps explaining IFN-γ levels that increased with parasitemia (Fig. 5C) in the absence of any changes in levels of tumor necrosis factor-α (TNF-α) (Fig. 5E), IL-1β (Fig. 5F), or IL-17 (Fig. 5G) during infection.