All Treg markers, but CD39 and CD45RA+CD31- were independently associated with clinical sepsis and not presumed sepsis, suggesting that the main phenotypic Treg characteristics identified in this study, such as Treg frequency, T effector frequency, Integrin α4β1and activation markers CTLA-4 and PD1 be associated with the development of neonatal sepsis. Here, CTLA4 is linked to Neonatal sepsis.