CCR9 and necrotizing enterocolitis: In addition, an increased frequency of a subset of Treg, namely C-C motif chemokine receptor 9 (CCR9)-positive interleukin 17 (IL-17) producing Treg with strongly impaired immunosuppressive capacities, was found in peripheral blood during NEC and the conversion of CCR9+ Treg into this IL-17 producing subset was promoted by IL-6 [144].