IL9 and infection: It is important to note that in the fight against infection by pathogens such as parasites, Th1 (with its primary cytokine, IFN-γ), Th2 (with its main cytokine, IL-4), Th9 (with its main cytokine, IL-9) and Th17 (with its main cytokine, IL-17) immune responses play a vital role [43–47].