IL21 and infection: Several studies have demonstrated that IL-21 is induced at both the mRNA and protein levels during natural infections with several species of schistosomes in humans and in murine models of schistosomiasis (Milner et al., 2010; Bourke et al., 2013; Zhang Y. et al., 2016), as well as following vaccination with schistosome-derived peptides (Zhang et al., 2013, 2018; Bourke et al., 2014; Fairfax et al., 2015).