By: Sophia Björkander

Host: Prof. Eva Sverremark-Ekström

Title: Phenotypes and functional characteristics of FOXP3+ (regulatory) T-cells in childhood and the influence of gut bacteria



T-regulatory cells (Tregs) protect from immune-mediated disease by regulating immune effector responses and by maintaining tolerance towards self-compounds and non-harmful antigens like allergens and commensal compounds. It is known that the gut microbiota influences general immune maturation in both mice and humans. In addition, commensal bacteria affect the maturation and function of Tregs in mice. Today, Treg maturation during childhood and the impact of the gut microbiota on peripheral Tregs has not been extensively studied in humans. Certain gut bacteria like Staphylococcus aureus (S. aureus) act as both commensal and pathogen, making them interesting to study in the context of immune regulation and Treg-function. 

In PAPER I, we explored the effects of S. aureus-supernatant (-sn) and Lactobacillus (L) reuteri-sn on adult Tregs in PBMC-cultures. In addition to production of IL-10, IL-17 and IFN-γ, S. aureus-sn induced increased expression of CTLA-4 and CD161 and an increased percentage of CD161+ Tregs. Further, we show that production of IFN-γ and IL-17 was higher within the CD161+ subpopulation, still there was significant production of cytokines also from CD161- cells. Based on expression of CD161 and HELIOS we identified four distinct Treg-populations that responded differentially to S. aureus-sn in terms of IFN-γ-production, showing that IFN-γ was linked to CD161 and not to HELIOS. Co-stimulation with L. reuteri-sn dampened S. aureus-sn-induced responses. Together, this data show that S. aureus-sn induces pleotropic and subpopulation specific activation of Tregs.     

In PAPER II, we investigated the phenotypic and functional features of Tregs in childhood in response to S. aureus-sn and if L. reuteri could dampen S. aureus-induced Treg-activation in vitro during childhood. CBMC/PBMC from children at birth, age two and age seven were compared to adult PBMC. The percentage of Tregs remained constant with age while the percentages of CD45RA+ and HELIOS+ Tregs decreased. However, the results show that CD45RA and HELIOS-expression is not completely linked. To investigate Treg-plasticity and TH-mimicking we evaluated CD161 and CXCR3 and found that Treg-expression of these markers positively correlated with age. Treg-capacity to produce IL-10, IL-17 and IFN-γ was impaired during childhood after stimulation with S. aureus-sn. Further, L. reuteri-sn was able to partly dampen S. aureus-induced Treg-activation also during childhood. Finally, early colonization with S. aureus and lactobacilli-strains associated with Treg-phenotype and IL-10-production. In conclusion, there is gradual maturation of Treg-phenotype and functional responses during childhood in response to microbial stimulation and colonization seems to influence peripheral Treg-maturation.