STAT3 and parasitic infectious disease: To conclude, we and others already have shown that, in synergy with IFN-γ, the IL-21/IL-21R axis is required for the optimal expression of ISGs, including several chemokines and chemokine receptors, as well MHC class molecules required for protection against parasitic infections, in a STAT3-independent, most likely STAT1-dependent, manner in humans or in mice (Wan et al., 2015; Solaymani-Mohammadi and Berzofsky, 2019).