IL9 and viral infectious disease: Genes like TLR-7, TLR-9, the transcriptional factor forkhead box P3, the chemokine receptor CXCR3, CD40L, and interleukin 9 (IL-9) are located on chromosome X and have been shown to influence cytokine production [i.e., tumor necrosis factor α (TNF-α), interferon α (IFN-α) production], and the ability to respond to viral infections differently in women when compared to men (Klein et al., 2010; Giefing-Kröll et al., 2015; Oghumu et al., 2019).