Interestingly, the transcription factor, IFN-stimulated gene factor 3 (ISGF3) induces the expression of the IL-27 subunit p28 by primed DCs, and IL-27 produced by DCs is required for the differentiation of TFH cells and the subsequent IL-21 expression by TFH cells during infections with trematodes, including S. mansoni and F. hepatica (Gringhuis et al., 2014). Here, IL21 is linked to infection.