IL9 and infection: In turn, the Th2 lymphocyte subpopulation produces interleukin-4 (IL-4), interleukin-5 (IL-5), interleukin-9 (IL-9), interleukin-10 (IL-10), etc., and is associated with susceptibility to infections, pathogenicity, and the survival of parasites in host tissues [18,19].