OP0268 Echerichia coli expands the proportion of helios+ natural CD25+CD127low/neg regulatory T cells in newborn children
Authors: A. Rudin, H. Rabe, A.-C. Lundell, I. Adlerberth, A.E. Wold
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> CD4<sup>+</sup> regulatory T cells (Tregs) in human newborns express FOXP3 and CTLA-4. Although they are naïve they are functional and essential in the maintenance of self-tolerance and immune homeostasis. Tregs can be subdivided into Helios<sup>+</sup> natural Tregs derived from the thymus and Helios<sup>–</sup> induced Tregs that are generated from conventional CD4 T cells in the periphery after stimulation. The gut microbiota is a stong stimulus for the development of the immune system in neonates and germ-free animal models have demonstrated that intestinal bacterial colonization is important for the induction of Tregs and tolerance. <h3>Objectives</h3> We here asked whether specific bacterial strains that colonize the human infant gut are able to expand the proportion of Tregs from newborns <i>in vitro</i>. We also asked whether the expanded cells were still suppressive and if they were dominated by natural or induced Tregs. Finally we asked whether an association could be found <i>in vivo</i> between early gut bacterial colonization and proportion of CTLA-4<sup>+</sup> putative Tregs. <h3>Methods</h3> Mononuclear cells were isolated from cord blood of healthy newborns and peripheral blood of healthy adults. We defined the regulatory T cells as the CD4+CD25+CD127<sup>low/neg</sup> T cells (Tregs) both in the subsequent cell sorting, the suppression assays and and when subdividing them into Helios<sup>+</sup> natural Tregs and peripherally induced Helios<sup>-</sup> Tregs. The cell cultures were stimulated with UV-killed bacteria isolated from infants, here <i>Escherichia coli</i>, <i>Staphylococcus aureus</i> or <i>Lactobacilli paracaseii</i>. We also analyzed the association between gut bacterial colonization and regulatory T cells in a prospective newborn-infant cohort of 64 children using multivariate factor analysis. <h3>Results</h3> The proportion of Tregs out of CD4+ cells was significantly lower in newborns compared to adults and newborns had a significantly higher fraction of Helios<sup>+</sup> natural Tregs compared to adults. Tregs from newborns suppressed autologous naïve CD4<sup>+</sup> responder cells equally well as Tregs from adults. Stimulation with <i>E. coli</i> significantly increased the proportion of Tregs of CD4<sup>+</sup> T cells in newborns in contrast to adults. When subdivided into natural Helios<sup>+</sup> and induced Helios<sup>–</sup> Tregs we found that the expansion of the Tregs in newborns was more pronounced in the natural than in the induced Treg fraction. The Tregs maintained their suppressive ability <i>in vitro</i> after bacterial stimulation. In the prospective newborn-infant cohort we found a positive association between early gut colonization with <i>E. coli</i> and proportion of CTLA-4<sup>+</sup> cells out of CD4<sup>+</sup> T cells at 1 month of age. <h3>Conclusions</h3> <i>E. coli</i> expands the proportion of preferentially Helios<sup>+</sup> natural CD25<sup>+</sup>CD127<sup>low/neg</sup> regulatory T cells from newborn children <i>in vitro</i> and these cells maintain their suppressive capacity. These results were supported by the finding that early colonization with <i>E. coli</i> and no other bacteria was associated with higher proportions of CTLA-4<sup>+</sup> cells of CD4<sup>+</sup> T cells in 1-month-old infants in the prospective newborn-infant cohort. Thus, early intestinal colonization with <i>E. coli</i> may play an important role in increasing the proportion of natural Tregs in infants, which may lead to development of stronger self-tolerance and immune homeostasis in children. <h3>Disclosure of Interest</h3> None Declared