Activated Umbilical Cord Blood Cells from Pre-term and Term Neonates Express CD69 and Synthesize IL-2 but Are Unable to Produce IFN-γ

Background. The immune response exhibits quantitative and qualitative differences throughout human development. Both phenotypical and functional immaturity of newborn immune cellular components have been reported. We aimed to analyze possible differences in cellular activation assessed by expression of surface CD69 and cytokine production in mononuclear peripheral blood cells from premature ( 37 weeks of gestation) neonates compared to adult donors. Methods. Ten persons from each group were selected; none was infected, immunodepressed, under medical treatment, or had any congenital abnormalities. Blood was obtained from umbilical cord of term and pre-term donors and vein punction of adults. All samples were collected in heparin and subsequently activated with PHA-L or PMA plus ionomycin at 37°C for 4 h. After incubation, cells were labeled to determine CD69 expression on CD3+CD4+, CD3+CD8+, CD19+, and CD16+56+ subpopulations. Intracellular staining was performed to analyze IFN-γ, IL-2, and CD69 in CD3+ cells. After staining, cells were analyzed by flow cytometry. Results. We first found a substantially higher number of CD3+CD4+CD69+ cells in premature and term neonates than in adults. Secondly, percentage of CD3+CD8+, CD56+, and CD19+ cells expressing CD69 was similar among the three groups. Thirdly, expression of CD69 was higher in CD19+ cells than in CD16+56+ cells of all three groups. Regarding cytokine production, IFN-γ was detected only in cells from adults and was consistent in all individuals analyzed. In sharp contrast, IL-2 and intracellular CD69 (iCD69) were detected in all three groups, with no significant differences among them. Induction of IL-2 and iCD69 showed that lack of response with IFN-γ was restricted to pre-term and newborn populations. Conclusions. In summary, our results showed that a) CD69 is an early activation marker of both mononuclear umbilical cord and peripheral blood cells activated by a mitogenic stimulus, and b) newborn CD3+ cells probably lack conditions required to progress through the activation process that leads to IFN-γ production. These conditions are still unknown but certainly constitute an interesting issue for further studies.