The early establishment of a complete microbiome has been shown to play an integral part in the development and maintenance of an intact intestine and its immune system, although much remains unknown about the specific mechanisms of immune modulation in newborns. In our study we show in a co-culture model of the undeveloped small intestine that members of Lactobacillus spp. influence STAT1 and NF-kB p65 nuclear translocation in both intestinal epithelial cells as well as underlying macrophages. Moreover, by using imaging flow cytometry we were able to monitor each individual cell and create a framework of the percentage of cells in which translocation occurred in challenged versus control cell populations. We also observed a significant difference in baseline translocation in intestinal cells when cultured alone versus those in a co-culture model, underpinning the importance of 3D models over monolayer set-ups in epithelial in vitro research. In conclusion, our work offers new insights into the potential routes by which the commensal microbiome primes the early immune system to fight pathogens, and shows how strain-specific these mechanisms really are.

The dynamic process of the development of the immune system can in itself result in age-related immune malfunctions. In this study, we analysed lymphocyte subsets in the peripheral blood of 60 healthy donors, divided into groups of children, adolescents, and adults, focusing on effector (Teff) and regulatory (Treg) T lymphocytes and STAT1/STAT5 signalling response in helper T lymphocytes (Th) in adults, using flow cytometry. Our results demonstrate a decrease in the percentage of total Tregs and an increase in the percentage of total Teffs with age and a consequential immense increase in the Teff/Treg ratio. The increase of Teffs was most apparent in Th1, Th1Th17, and Th17CD161− subsets. Significant Th lymphocyte STAT1 expression differences were observed between children and adolescents, which were associated with the decrease in activated Tregs. Higher expression of STAT1 was found in FoxP3hi than in FoxP3low Th lymphocytes, while significant IL-2 induced STAT5 phosphorylation differences were found among the subsets of Th lymphocytes in adults. Our study demonstrates age-related changes in circulating Teff and Treg, as well as significant differences in STAT5/STAT1 signalling among FoxP3+ Th lymphocytes, providing new advances in the understanding of immunosenescence.

In murine systemic lupus erythematosus (SLE), aberrant regulation of interferon (IFN)-alpha-STAT1 signaling and perturbed homeostasis of CD4⁺FOXP3⁺ regulatory T cells (Tregs) were described. In the present study, STAT1 signaling and circulating Treg subsets were assessed by flow cytometry in 39 SLE patients and their potential association with disease course was examined during long-term follow-up. Levels of STAT1 protein as measured by median fluorescence intensity (MFI) were significantly increased in SLE CD4 T cells when compared with rheumatoid arthritis patients and healthy controls and were positively correlated with disease activity. The highest STAT1 MFI was found in CD45RA^-FOXP3^hi-activated Treg (aTreg) subset, which demonstrated the highest STAT1 phosphorylation responses among SLE CD4 T cells and significant decrease in proliferation marker Ki-67 expression after IFN-alpha stimulation. Percentage of Ki-67⁺ aTregs was significantly decreased in SLE patients and was negatively correlated with CD4 T cell STAT1 MFI. A subgroup of SLE patients characterized by lower aTreg counts experienced more severe relapsing disease course during 1,000 days of follow-up. Mean CD4 T cell STAT1 MFI in follow-up samples from SLE patients was negatively correlated with mean of follow-up aTreg counts. Our findings indicate that augmented STAT1 signaling may be involved in perturbed aTreg homeostasis, which could represent a possible marker of SLE disease severity.