Abnormalities in CD4+CD25+Foxp3+ regulatory T (T reg) cells have been implicated in susceptibility to allergic, autoimmune, and immunoinflammatory conditions. However, phenotypic and functional assessment of human T reg cells has been hampered by difficulty in distinguishing between CD25-expressing activated and regulatory T cells. Here, we show that expression of CD127, the α chain of the interleukin-7 receptor, allows an unambiguous flow cytometry–based distinction to be made between CD127lo T reg cells and CD127hi conventional T cells within the CD25+CD45RO+RA− effector/memory and CD45RA+RO− naive compartments in peripheral blood and lymph node. In healthy volunteers, peripheral blood CD25+CD127lo cells comprised 6.35 ± 0.26% of CD4+ T cells, of which 2.05 ± 0.14% expressed the naive subset marker CD45RA. Expression of FoxP3 protein and the CD127lo phenotype were highly correlated within the CD4+CD25+ population. Moreover, both effector/memory and naive CD25+CD127lo cells manifested suppressive activity in vitro, whereas CD25+CD127hi cells did not. Cell surface expression of CD127 therefore allows accurate estimation of T reg cell numbers and isolation of pure populations for in vitro studies and should contribute to our understanding of regulatory abnormalities in immunopathic diseases.

Preeclampsia is the leading cause of morbidity and mortality in pregnancy. Although the etiology of preeclampsia is still unclear, it is believed to involve rejection of the fetus, possibly due to an imbalance between regulatory (Treg) and effector T cells. To test this, we compared the frequencies of circulating CD4⁺ T cells expressing Foxp3, IFN-γ, IL-10, or IL-17 at the end of the third trimester of healthy and preeclamptic pregnancies. The size of the Treg cell compartment, defined by the frequency of CD4⁺CD25^high, CD4⁺CD127^lowCD25⁺, and CD4⁺Foxp3⁺ cells was significantly higher in normal compared with preeclamptic pregnancies. CD4⁺CD25^high and CD4⁺CD127^lowCD25⁺ populations in preeclampsia were not significantly different from those in nonpregnant controls, whereas CD4⁺Foxp3⁺ cells numbersre slightly lower in preeclampsia. The suppressive activity of ex vivo-sorted CD4⁺CD127^lowCD25⁺ Treg cells was not significantly different between the three study groups. The percentage of CD4⁺IL-17-producing T cells decreased significantly in healthy compared with preeclamptic pregnancies and nonpregnant controls, whereas CD4⁺IL-10- and CD4⁺IFN-γ-producing cells remained unchanged. Consequently, the ratio of Foxp3⁺ Treg to IL-17-expressing CD4⁺ T cells was significantly increased in healthy but not in preeclamptic pregnancies. Thus, preeclampsia is associated with the absence of normal systemic skewing away from IL-17 production toward Foxp3⁺ expression. Finally, preeclamptic women had significantly higher levels of soluble endoglin, an inhibitor of TGF-β receptor signaling, which may bias toward IL-17 production. These results suggest that homeostasis between regulatory and proinflammatory CD4⁺ T cells might be pivotal for the semiallogeneic fetus to be tolerated within the maternal environment.

Foxp3⁺ regulatory T cells (Tregs) play essential roles in maintaining the immune balance. Although the majority of Tregs are formed in the thymus, increasing evidence suggests that induced Tregs (iTregs) may be generated in the periphery from naive cells. However, unlike in the murine system, significant controversy exists regarding the suppressive capacity of these iTregs in humans, especially those generated in vitro in the presence of TGF-β. Although it is well known that IL-10 is an important mediator of Treg suppression, the action of IL-10 on Tregs themselves is less well characterized. In this article, we show that the presence of IL-10, in addition to TGF-β, leads to increased expansion of Foxp3⁺ iTregs with enhanced CTLA-4 expression and suppressive capability, comparable to that of natural Tregs. This process is dependent on IL-10R–mediated STAT3 signaling, as supported by the lack of an IL-10 effect in patients with IL-10R deficiency and dominant-negative STAT3 mutation. Additionally, IL-10–induced inhibition of Akt phosphorylation and subsequent preservation of Foxo1 function are critical. These results highlight a previously unrecognized function of IL-10 in human iTreg generation, with potential therapeutic implications for the treatment of immune diseases, such as autoimmunity and allergy.

Regulatory T cells (TREGs) constitutively expressing CD4, CD25, and the transcription factor Foxp3 can prevent a wide range of experimental and spontaneous autoimmune diseases in mice. In humans, CD4+CD25bright T cells, predominantly within the CD45RO+ activated/memory subset in adults and the CD45RA+ naive T-cell subset in infants, are considered to be the equivalent subset. Using novel combinations of monoclonal antibodies (mAbs), we examined expression of CD25 in human infant thymus, cord blood, adult peripheral blood, lymph node, and spleen. In addition to the CD4+CD25bright T cells, subfractionation on the basis of CD45 splice variants indicated that all samples contained a second distinct population of cells expressing a slightly lower level of CD25. In adult peripheral blood, this population expressed a naive CD45RA+ phenotype. The corresponding population in lymph node, spleen, and cord blood showed some evidence of activation, and expressed markers characteristic of TREGs, such as cytotoxic T lymphocyte-associated antigen 4 (CTLA-4). Sorted CD4+CD25+CD45RA+ T cells from both cord and adult blood expressed very high levels of mRNA for Foxp3 and manifested equivalent suppressive activity in vitro, indicating that they are bone fide members of the regulatory T-cell lineage. Targeting naive TREGs in adults may offer new means of preventing and treating autoimmune disease.

Extracellular vesicles (EVs) are blebs of either plasma membrane or intracellular membranes carrying a cargo of proteins, nucleic acids, and lipids. EVs are produced by eukaryotic cells both under physiological and pathological conditions. Genetic and environmental factors (diet, stress, etc.) affecting EV cargo, regulating EV release, and consequences on immunity will be covered. EVs are found in virtually all body fluids such as plasma, saliva, amniotic fluid, and breast milk, suggesting key roles in immune development and function at different life stages from in utero to aging. These will be reviewed here. Under pathological conditions, plasma EV levels are increased and exacerbate immune activation and inflammatory reaction. Sources of EV, cells targeted, and consequences on immune function and disease development will be discussed. Both pathogenic and commensal bacteria release EV, which are classified as outer membrane vesicles when released by Gram-negative bacteria or as membrane vesicles when released by Gram-positive bacteria. Bacteria derived EVs can affect host immunity with pathogenic bacteria derived EVs having pro-inflammatory effects of host immune cells while probiotic derived EVs mostly shape the immune response towards tolerance.