No abstract

The regulatory T (Treg) cells restrain immune responses through suppressor-function elaboration that is dependent upon expression of the transcription factor Foxp3. Despite a critical role for Treg cells in maintaining lympho-myeloid homeostasis, it remains unclear whether a single mechanism or multiple mechanisms of Treg cell-mediated suppression are operating in vivo and how redundant such mechanisms might be. Here we addressed these questions by examining the role of the immunomodulatory cytokine IL-10 in Treg cell-mediated suppression. Analyses of mice in which the Treg cell-specific ablation of a conditional IL-10 allele was induced by Cre recombinase knocked into the Foxp3 gene locus showed that although IL-10 production by Treg cells was not required for the control of systemic autoimmunity, it was essential for keeping immune responses in check at environmental interfaces such as the colon and lungs. Our study suggests that Treg cells utilize multiple means to limit immune responses. Furthermore, these mechanisms are likely to be nonredundant, in that a distinct suppressor mechanism most likely plays a prominent and identifiable role at a particular tissue and inflammatory setting.

Nitric oxide (NO) is important in many biological functions. It is generated from L-arginine by the enzyme NO synthase (NOS). The cytokine-inducible NOS (iNOS) is activated by several immunological stimuli, leading to the production of large quantities of NO which can be cytotoxic. To define the biological role of iNOS further, we generated iNOS mutant mice. These are viable, fertile and without evident histopathological abnormalities. However, in contrast to wild-type and heterozygous mice, which are highly resistant to the protozoa parasite Leishmania major infection, mutant mice are uniformly susceptible. The infected mutant mice developed a significantly stronger Th1 type of immune response than the wild-type or heterozygous mice. The mutant mice showed reduced nonspecific inflammatory response to carrageenin, and were resistant to lipopolysaccharide-induced mortality.

The interleukin 2 receptor y chain (IL-2R'y) is a component of the receptors for IL-2, IL-4, IL-7, and IL-15. Mutations in IL-2Ry in man appear responsible for the X chromosome-linked immunodeficiency SCIDX1, characterized by a defect in T-cell and natural killer (NK)-cell differentiation with the presence of poorly functioning B cells. To explore at which level IL-2Ry affects lymphoid development in vivo, we have analyzed mice derived from embryonic stem (ES) cells with mutant IL-2Ry loci generated by Cre/loxPmediated recombination. In the peripheral blood of chimeric animals, lymphoid cells derived from IL-2Ry-ES cells were not detected, although control ES cells carrying an IL-2R'y gene with embedded loxP sites gave rise to T-, B-, and NK-cell lineages. Germline IL-2Ry-deficient male animals, however, developed some mature splenic B and T cells, although the absolute number of lymphocytes was almost 10-fold reduced. In contrast, there was a complete disappearance of NK cells (over 350-fold reduction). Development of gut-associated intraepithelial lymphocytes was also severely diminished, and Peyer's patches were not detected. In vitro mitogenic responses of thymocytes, IL-4-directed immunoglobulin class switch of splenocytes, and NK activity were defective. Thus, IL-2Ry facilitates mainstream B-and T-cell generation and function and also appears to be essential for NK-cell development.Lymphoid development results from the expansion and differentiation of committed precursor cells under the influence of the bone marrow, thymic, and gut microenvironments, which requires both stem cell-stromal cell contact and interactions between soluble cytokines and their receptors (1, 2). The interleukin 2 receptor y chain (IL-2Ry), initially identified as an effector component of the IL-2R (3), figures prominantly in lymphopoiesis, through its participation in the receptors for IL-2, IL-4, IL-7, and IL-15 (4-8). Severe combined immunodeficiency Xl (SCIDX1), an X chromosomelinked immunodeficiency characterized by a severe block in T-cell and NK-cell differentiation with the presence of normal or elevated numbers of poorly functioning B cells (9, 10), is associated with mutations in IL-2Ry (11). Still, the level at which IL-2Ry mutations disrupt normal cytokine/receptor function and cause SCIDX1 is not known.A variety of lymphokines play a role in the early stages of lymphoid development. In mice, in vivo blockade of the IL-7/IL-7R system with antibodies results in a complete block in B-cell generation and a substantial decrease in T lymphopoiesis (12, 13). In contrast, mice deficient for IL-2, IL-4, or both lymphokines have normal numbers of mature B and T cells (14-16). Therefore the phenotype in human SCIDX1 (near absence of T cells, elevated proportions of B cells) cannot be easily explained by defects in the IL-2, IL-4, or IL-7 receptor systems, without a species-specific difference in receptor function. In addition, the use of IL-2Ry in additional cytokine receptors (such as IL-15R and perhaps others) and the r...

Previous studies in vivo have shown that IL-10 infusion can prevent lethal endotoxic shock. Mice deficient in the production of IL-10 (IL1OT) were used to investigate the regulatory role of IL-10 in the responses to LPS in three experimental systems. In a model of acute endotoxic shock, it was found that the lethal dose of LPS for IL1OT mice was 20-fold lower than that for wild type (wt) mice suggesting that endogenous IL-10 determines the amount of LPS which can be tolerated without death. The high mortality rate of IL1OT mice challenged with modest doses of LPS was correlated to the uncontrolled production of TNF as treatment with anti-TNF antibody (Ab) resulted in 70% survival. Additional studies suggested that IL-10 mediates protection by controlling the early effectors of endotoxic shock (e.g., TNFa) and that it is incapable of directly antagonizing the production and/or actions of late appearing effector molecules (e.g., nitric oxide). We also found that ILAOT mice were extremely vulnerable to a generalized Shwartzman reaction where prior exposure to a small amount of LPS primes the host for a lethal response to a subsequent sublethal dose. The priming LPS dose for IL1OT mice was 100-fold lower than that required to prime wt mice implying that IL-10 is important for suppressing sensitization. In agreement with this assumption, IL-10 infusion was found to block the sensitization step. Interestingly, IL-10 was not the main effector of endotoxin tolerance as ILAOT mice could be tolerized to LPS. Furthermore, IL-10 infusion could not substitute for the desensitizing dose of LPS. These results show that IL-10 is a critical component of the host's natural defense against the development of pathologic responses to LPS although it is not responsible for LPS-induced tolerance. (J. Clin. Invest. 1995Invest. . 96:2339Invest. -2347

Infection with the malaria parasite, Plasmodium, is characterized by excessive inflammation. The establishment of a precise balance between the pro- and anti-inflammatory responses is critical to guarantee control of the parasite and survival of the host. Interleukin (IL)-10, a key regulatory cytokine produced by many cells of the immune system, has been shown to protect mice against pathology during acute Plasmodium chabaudi chabaudi AS model of malaria. However, the critical cellular source of IL-10 is still unknown. Here, we demonstrate that T cell-derived IL-10 is necessary for the control of pathology during acute malaria, as mice bearing specific deletion of Il10 in T cells fully reproduce the phenotype observed in Il10−/− mice, with significant weight loss, drop in temperature and increased mortality. Furthermore, we show that IFN-γ+ Th1 cells are the main producers of IL-10 throughout acute infection, expressing high levels of CD44 and ICOS and low levels of CD127. Although Foxp3+ regulatory CD4+ T cells produce IL-10 during infection, highly activated IFN-γ+ Th1 cells were shown to be the essential and sufficient source of IL-10 to guarantee protection against severe immune-mediated pathology. Finally, in this model of malaria we demonstrate that the generation of protective IL10+IFN-γ+ Th1 cells is dependent on IL-27 signaling, and independent of IL-21.

No abstract

The idea that stem cell therapies work only via cell replacement is challenged by the observation of consistent intercellular molecule exchange between the graft and the host. Here we defined a mechanism of cellular signaling by which neural stem/precursor cells (NPCs) communicate with the microenvironment via extracellular vesicles (EVs), and we elucidated its molecular signature and function. We observed cytokine-regulated pathways that sort proteins and mRNAs into EVs. We described induction of interferon gamma (IFN-γ) pathway in NPCs exposed to proinflammatory cytokines that is mirrored in EVs. We showed that IFN-γ bound to EVs through Ifngr1 activates Stat1 in target cells. Finally, we demonstrated that endogenous Stat1 and Ifngr1 in target cells are indispensable to sustain the activation of Stat1 signaling by EV-associated IFN-γ/Ifngr1 complexes. Our study identifies a mechanism of cellular signaling regulated by EV-associated IFN-γ/Ifngr1 complexes, which grafted stem cells may use to communicate with the host immune system.