IL17A and necrotizing enterocolitis: Recently, it was demonstrated that NEC is associated with elevated blood levels of CCR9 + CD4 + T cells as well as CCR9 + interleukin-17 (IL-17) producing Treg (previously called regulatory T cells); the histological NEC severity is positively and negatively correlated with their gut and blood concentration, respectively (Ma et al., 2019).