Cytokine regulation of lung Th17 response to airway immunization using LPS adjuvant.

Infections caused by bacteria in the airway preferentially induce a Th17 response. However, the mechanisms involved in the regulation of CD4 T-cell responses in the lungs are incompletely understood. Here, we have investigated the mechanisms involved in the regulation of Th17 differentiation in the lungs in response to immunization with lipopolysaccharide (LPS) as an adjuvant. Our data show that both Myd88 and TRIF are necessary for Th17 induction. This distinctive fate determination can be accounted for by the pattern of inflammatory cytokines induced by airway administration of LPS. We identified the production of interleukin (IL)-1ß and IL-6 by small macrophages and IL-23 by alveolar dendritic cells (DCs), favoring Th17 responses, and IL-10 repressing interferon (IFN)-γ production. Furthermore, we show that exogenous IL-1ß can drastically alter Th1 responses driven by influenza and lymphocytic choriomeningitis virus infection models and induce IL-17 production. Thus, the precision of the lung immune responses to potential threats is orchestrated by the cytokine microenvironment, can be repolarized and targeted therapeutically by altering the cytokine milieu. These results indicate that how the development of Th17 responses in the lung is regulated by the cytokines produced by lung DCs and macrophages in response to intranasal immunization with LPS adjuvant.

The TNF-family cytokine TL1A promotes allergic immunopathology through group 2 innate lymphoid cells.

The tumor necrosis factor (TNF)-family cytokine TL1A (TNFSF15) costimulates T cells and promotes diverse T cell-dependent models of autoimmune disease through its receptor DR3. TL1A polymorphisms also confer susceptibility to inflammatory bowel disease. Here, we find that allergic pathology driven by constitutive TL1A expression depends on interleukin-13 (IL-13), but not on T, NKT, mast cells, or commensal intestinal flora. Group 2 innate lymphoid cells (ILC2) express surface DR3 and produce IL-13 and other type 2 cytokines in response to TL1A. DR3 is required for ILC2 expansion and function in the setting of T cell-dependent and -independent models of allergic disease. By contrast, DR3-deficient ILC2 can still differentiate, expand, and produce IL-13 when stimulated by IL-25 or IL-33, and mediate expulsion of intestinal helminths. These data identify costimulation of ILC2 as a novel function of TL1A important for allergic lung disease, and suggest that TL1A may be a therapeutic target in these settings.

IL-1ß strikingly enhances antigen-driven CD4 and CD8 T-cell responses.

Protective immune response requires massive expansion of antigen-triggered naïve cells, extensive differentiation into effector cells, migration of effectors into the periphery, and generation of a functional memory compartment. IL-1ß strikingly enhances expansion of antigen-primed CD8 and CD4 T cells in vivo. Its T-cell expansion in lymph nodes and spleen was direct, requiring that the stimulated T cells express IL-1R1. Immunization in the presence of IL-1ß increases the frequency of IL-17- and IFN-γ-producing cells among primed CD4 cells and the frequency of granzyme B-expressing and IFN-γ-producing cells and of cytotoxic cells among primed CD8 cells. IL-1ß-induced increase in the number of the activated CD4 and CD8 cells and augmented differentiation of the antigen-triggered T cells is very pronounced in liver and lungs. CD4 and CD8 cells primed in the presence of IL-1ß display augmented cell number and enhanced cytokine production when rechallenged 2 mo after priming with antigen and lipopolysaccharide (LPS). In five in vivo models, IL-1ß enhanced the protective value of weak vaccines. Preliminary analysis of in vivo gene expression in CD4 cells stimulated with IL-1ß revealed that IL-1ß caused gene expression changes consistent with the up-regulation of pathways involved in cell replication, cell survival, and enhanced energy metabolism. Thus, IL-1ß enhances antigen-primed CD4 and CD8 T-cell expansion, differentiation, and migration to the periphery and memory, the specific functions required for generation of effective protective immune responses.

Fibrosin, a novel fibrogenic cytokine, modulates expression of myofibroblasts.

Granulation tissue fibroblasts, or myofibroblasts are characterized by the presence of alpha smooth muscle actin fibers (alpha SMA). These specialized cells are involved in wound contraction and in retractile phenomena observed during fibrotic disease. Myofibroblasts have also been shown to play a role in embryonic development. Growth factors such as Transforming growth factor beta TGFbeta and Nerve growth factor (NGF) can modulate the differentiation of myofibroblasts. In this report, we show that in vitro application of fibrosin, a novel fibrogenic cytokine, stimulates expression of alpha SMA-producing cells at least four-fold above that observed in control cultures. In addition, administration of fibrosin in a wound healing model in mice stimulates increased numbers of myofibroblasts 7 days after injury, when compared with untreated, or, control, wounded mice. These results suggest that fibrosin plays an important role in up regulating the appearance of myofibroblasts during wound healing, and possibly in fibrotic diseases. It may, therefore, be important in the process of scarring.

T-bet is rapidly induced by interferon-gamma in lymphoid and myeloid cells.

Differentiation of naive CD4(+) T cells into IFN-gamma-producing T helper 1 (T(H)1) cells is pivotal for protective immune responses against intracellular pathogens. T-bet, a recently discovered member of the T-box transcription factor family, has been reported to play a critical role in this process, promoting IFN-gamma production. Although terminal T(H)1 differentiation occurs over days, we now show that challenge of mice with a prototypical T(H)1-inducing stimulus, Toxoplasma gondii soluble extract, rapidly induced IFN-gamma and T-bet; T-bet induction was substantially lower in IFN-gamma-deficient mice. Naive T cells expressed little T-bet, but this transcription factor was induced markedly by the combination of IFN-gamma and cognate antigen. Human myeloid antigen-presenting cells showed T-bet induction after IFN-gamma stimulation alone, and this induction was antagonized by IL-4 and granulocyte/macrophage colony-stimulating factor. Although T-bet was induced rapidly and directly by IFN-gamma, it was not induced by IFN-alpha, lipopolysaccharide, or IL-1, indicating that this action of IFN-gamma was specific. Moreover, T-bet induction was dependent on Stat1 but not Stat4. These data argue for a model in which IFN-gamma gene regulation involves an autocrine loop, whereby the cytokine regulates a transcription factor that promotes its own production. These findings substantially alter the current view of T-bet in IFN-gamma regulation and promotion of cell-mediated immune responses.

Autoreactivity, dynamic tuning and selectivity.

The immune system adjusts its response to the context in which antigens, including self-antigens, are recognized. Recent observations support a conceptual framework for understanding how this may be achieved at the cellular and cell-population levels. At both levels, 'perturbations' elicit competition between excitation and de-excitation, resulting either in adaptation or in various responses. The responsiveness of individual cells is dynamically tuned, reflecting their recent experience. The tuning of T-cell activation thresholds by self-ligands facilitates positive selection and continuously regulates the level of autoreactivity in the periphery. Autoreactivity appears to be involved in regulation of the immune response, homeostasis, maintaining of the functional integrity of naïve and memory cells, and in other physiological functions.

Interferon gamma stabilizes the T helper cell type 1 phenotype.

T helper cell (Th)1-primed CD4 T cells from wild-type donors make little interleukin (IL)-4 when restimulated under Th2 conditions. However, such restimulation of Th1-primed cells from interferon (IFN)-gamma(2/-) or IFN-gamma receptor (IFN-gammaR)(-/-) mice resulted in substantial production of IL-4 and other Th2 cytokines. Adding IFN-gamma to the priming culture markedly diminished the capacity of Th1-primed IFN-gamma(2/-) cells to express IL-4. Even IFN-gamma-producing cells from IFN-gammaR(-/-) mice could acquire IL-4-producing capacity. Thus, IFN-gamma is not required for the development of IFN-gamma-producing capacity, but it plays a critical role in suppressing the IL-4-producing potential of Th1 cells.

Stat6 is necessary and sufficient for IL-4's role in Th2 differentiation and cell expansion.

IL-4 plays a critical role in the differentiation of TCR-stimulated naive CD4 T cells to the Th2 phenotype. In response to IL-4, the IL-4R activates a set of phosphotyrosine binding domain-containing proteins, including insulin receptor substrate 1/2, Shc, and IL-4R interacting protein, as well as Stat6. Stat6 has been shown to be required for Th2 differentiation. To determine the roles of the phosphotyrosine binding adaptors in Th2 differentiation, we prepared a retrovirus containing a mutant of the human (h)IL-4R alpha-chain, Y497F, which is unable to recruit these adaptors. The mutant hIL-4Ralpha, as well as the wild-type (WT) hIL-4Ralpha, was introduced into naive CD4 T cells. Upon hIL-4 stimulation, Y497F worked as well as the WT hIL-4Ralpha in driving Th2 differentiation, as measured by Gata3 up-regulation and IL-4 production. Furthermore, IL-4-driven cell expansion was also normal in the cells infected with Y497F, although cells infected with Y497F were not capable of phosphorylating insulin receptor substrate 2. These results suggest that the signal pathway mediated by Y497 is dispensable for both IL-4-driven Th2 differentiation and cell expansion. Both WT and Y497F hIL-4Ralpha lose the ability to drive Th2 differentiation and cell expansion in Stat6-knockout CD4 T cells. A constitutively activated form of Stat6 introduced into CD4 T cells resulted in both Th2 differentiation and enhanced cell expansion. Thus, activated Stat6 is necessary and sufficient to mediate both IL-4-driven Th2 differentiation and cell expansion in CD4 T cells.

Disrupting Il13 impairs production of IL-4 specified by the linked allele.

Interleukin 13-deficient (IL-13-/-) mice express a defect in priming for IL-4 production that is not corrected by adding IL-13 to the priming culture. This is partly accounted for by the consumption of IL-4 without endogenous replacement during culture of IL-13-/- CD4+ T cells. We examined cells from mice in which disrupted Il13 was linked to wild-type Il4 on one chromosome and wild-type Il13 was linked to a "knocked-in" green fluorescent protein (Gfp) gene in the Il4 locus. Our results show that the deficit in IL-4 production was due, at least in part, to a cis effect, in which disrupted Il13 diminished IL-4 production from the linked Il4 gene.

Regulation of expression of IL-4 alleles: analysis using a chimeric GFP/IL-4 gene.

CD4 cells from mice heterozygous for an IL-4 and a GFP/IL-4 gene frequently express a single allele. Analysis of IL-4 or GFP production by cells from recently primed Th2 cells indicates that essentially all are competent to transcribe either allele but have a low probability of doing so. By contrast, long-term Th2 clones show distinct and heritable ratios in the proportion of cells that express IL-4 or GFP. We conclude that in the course of Th2 priming an early efficient event renders both alleles capable of being inefficiently transcribed; a second, less frequent event occurs that renders one allele more competent, accounting for the differential expression of IL-4 and GFP in different clones.

Lack of skin fibrosis in tight skin (TSK) mice with targeted mutation in the interleukin-4R alpha and transforming growth factor-beta genes.

Scleroderma is a disorder characterized by fibrosis of the skin and internal organs and autoimmunity. Whereas the cause is unknown, interleukin-4 and transforming growth factor-beta have been postulated to play a major part in the fibrosis. To investigate the part played by these cytokines, we prepared TSK/+ mice with a targeted mutation in the interleukin-4R alpha or transforming growth factor-beta genes. The breeding failed to produce TSK/+ transforming growth factor-beta -/- mice so analysis of the role of transforming growth factor-beta was limited to TSK/+ transforming growth factor-beta +/- mice. We observed that TSK/+ interleukin-4R alpha -/- did not develop dermal thickening, and deletion of one allele of the transforming growth factor-beta gene resulted in diminished dermal thickness compared with TSK/+ mice; however, the deletion of interleukin-4R alpha or transforming growth factor-beta had no effect on lung emphysema, which is another characteristic of TSK syndrome. Electron microscopic analysis of skin showed that the collagen fibrils in TSK/+ interleukin-4R alpha -/- mice exhibit normal periodicity but have a smaller diameter than the fibers found in C57BL/6 mice. Analysis of skin and serum samples showed that the deletion of interleukin-4R alpha or one allele of transforming growth factor-beta prevented the increase of skin thickness paralleled with a decrease in the dermal hydroxyproline content and development of autoantibodies associated with TSK syndrome. These results demonstrate the importance of interleukin-4 and transforming growth factor-beta for the development of cutaneous fibrosis in vivo and suggest an important part for these cytokines in wound healing and connective tissue maintenance in general.

Cell division is not a "clock" measuring acquisition of competence to produce IFN-gamma or IL-4.

Naive CD4 T cells acquire the potential to produce IFN-gamma and IL-4 by culture in the presence of their cognate Ag, APC, and appropriate cytokines. In this study, we show that commitment to IFN-gamma production on the part of rigorously purified naive CD4 T cells can occur without cell division. Indeed, even entry into S phase is not essential. Moreover, both CD4 and CD4/CD8 thymocytes from TCR-transgenic mice (5CC7 mice) on a Rag2(-/-) background can acquire IFN-gamma-producing capacity when stimulated by peptide, APC, and IL-12. These cells can do so without dividing and some acquire IFN-gamma-producing activity without entry into S phase. Not only is cell division not required for acquisition of cytokine-producing potential, cell populations that have undergone the same numbers of divisions can have quite different proportions of IFN-gamma- or IL-4-producing cells, depending on the duration of priming or, in the case of IL-4, on the concentration of peptide. Thus, cell division is not a clock for the expression of these cytokines. Factors associated with priming conditions including strength of stimulation, duration of priming, and number of divisions each play a role.

Conventional, naive CD4+ T cells provide an initial source of IL-4 during Th2 differentiation.

IL-4 is known to promote the differentiation of CD4+ T cells into IL-4-secreting Th2 cells. However, the cellular source of the early burst of IL-4 that drives Th2 responses in vivo has not been conclusively identified. Mice deficient for the IL-4 receptor alpha-chain (IL-4Ralpha-/-) retain the capacity to secrete IL-4 and can be used to identify those cell types that produce IL-4 without a requirement for prior IL-4-mediated stimulation. To address whether naive, conventional CD4+ T cells may act as initial producers of IL-4 in Ag-specific responses, we crossed the BALB/c IL-4Ralpha-/-mice to DO11.10/scid TCR transgenic mice. Lymph node cells from wild-type and IL-4Ralpha-/- DO11.10/scid mice secreted approximately 50 pg of IL-4 per10(6) cells within 48 h after peptide stimulation. This small amount of IL-4 was sufficient to cause the differentiation of wild-type CD4+ T cells into Th2 cells, particularly if IFN-gamma and IL-12 were neutralized during the priming cultures. CD4+ cells from the IL-4Ralpha-/- mice gave rise to a minor proportion (approximately 2%) of IL-4-producing cells upon stimulation in the presence of anti-IFN-gamma and anti-IL-12. These data show that conventional, naive CD4+ T cells may be considered as initial sources of IL-4 and, in the absence of IFN-gamma and IL-12, this IL-4 can induce Th2 polarization.

Transient inhibition of interleukin 4 signaling by T cell receptor ligation.

Interleukin (IL)-4 and IL-12 together with T cell receptor (TCR) engagement are crucial for the differentiation of CD4(+) T cells into T helper (Th)2 or Th1 cells, respectively. Although IL-4 receptors (IL-4Rs) but not IL-12Rs are expressed on naive CD4(+) T cells, IL-4 has no apparent advantage over IL-12 in driving naive T cell differentiation when the cells are primed with both IL-4 and IL-12 in vitro. It was found that IL-4-induced phosphorylation of Janus kinases 1 and 3, IL-4R alpha, signal transducer and activator of transcription 6, and insulin receptor substrate 2 was strikingly but transiently inhibited by TCR ligation both in conventional and TCR transgenic T cells. TCR engagement also blocked the expression of an IL-4-inducible gene. Signals induced by other cytokines, including IL-2, IL-6, and interferon alpha, but not by insulin-like growth factor 1, were also blocked by TCR engagement. The capacity of various inhibitors to reverse TCR-mediated inhibition of IL-4 signaling suggested that activation of the Ras-mitogen-activated protein kinase pathway and of the calcineurin pathway contribute to desensitizing IL-4R. IL-4 responsiveness returned at about the time ( approximately 12 h) that IL-12-mediated signaling was first observed. Thus, through different mechanisms, neither IL-4R nor IL-12R has any clear advantage in polarizing cells; rather, the availability of cytokine is probably the limiting factor in this process.

A targeted mutation in the IL-4Ralpha gene protects mice against autoimmune diabetes.

Autoimmune insulin-dependent diabetes mellitus (IDDM) occurs spontaneously in mice-bearing transgenes encoding the influenza hemagglutinin under the control of the rat insulin promoter and a T cell receptor specific for an hemagglutinin peptide associated with I-E(d). Such "double transgenic" mice expressing wild-type or targeted IL-4Ralpha genes were examined for the onset of IDDM. Eight of 11 mice homozygous for wild-type IL-4Ralpha were hyperglycemic by 8 weeks of age, whereas only 1 of 16 mice homozygous for the targeted allele were hyperglycemic at this time. Most 1L-4Ralpha-/- mice remained normoglycemic to 36 weeks of age. Although only 10% of double transgenic mice homozygous for the wild-type IL-4Ralpha allele survived to 30 weeks, 80% of mice homozygous for the targeted allele did so. Heterozygous mice displayed an intermediate frequency of diabetes. Even as late as 270 days of age, mice homozygous for the targeted allele had no insulitis or only peri-insulitis. Thus, the inability to respond to IL-4 and/or IL-13 protects mice against IDDM in this model of autoimmunity.

Self-tolerance: context dependent tuning of T cell antigen recognition.

Physiological messages to cells are encoded in the magnitude, and in the time- and space-contingencies, of sets of stimuli. In particular, individual T cells continuously integrate antigenic and other signals and respond differentially to the rate of change in the level of stimulation, translated intracellularly into 'metabolic perturbations'. The organization of the immune response at the cell-population level in space and time is also conductive to discriminating the magnitude of 'system perturbations'. In this way, the immune system was 'designed' to respond in a characteristic explosive way mainly to episodes of infection and not to the continuous presence of self-antigens. T cells are selected to be moderately autoreactive, and the degree of autoreactivity that they express is continuously controlled through activation-threshold tuning. Their level of autoreactivity is maintained in a range that facilitates survival and self-renewal and is probably used in performing some immunoregulatory functions and possibly other physiological functions. Autoreactivity and outward-directed immunity are regulated simultaneously and interactively through the interplay of selection, tuning, controlled activation and feedback.

Survival and cytokine polarization of naive CD4(+) T cells in vitro is largely dependent on exogenous cytokines.

Naive CD4(+) T cells differ from memory cells by their heightened expression of the disialoceramide recognized by antibody 3G11. 3G11(bright) cells respond well to immobilized anti-CD3 / anti-CD28 and to their cognate antigens but produce little or no IFN-gamma or IL-4 "acutely" and undergo cell death even in the presence of IL-2. They can be rescued by IL-4, IL-6 or IL-12. IL-6 is particularly notable since it is neutral in regard to Th1 / Th2 priming, allowing an assessment of the role of endogenous IL-4 in priming for IL-4 production. Naive TCR-transgenic BALB / c scid T cells cultured with an ovalbumin peptide and IL-4(- / -) antigen-presenting cells in the presence of IL-6 showed a modest degree of priming for IL-4 production if both IFN-gamma and IL-12 were neutralized. This priming is far less than that observed if IL-4 is added to the priming culture. These results indicate that IL-4 production as a result of TCR engagement is sufficient for only a minor component of the polarization observed when unseparated BALB / c CD4 T cell populations are primed or when IL-4 is intentionally added to the priming culture.

Single cell analysis reveals that IL-4 receptor/Stat6 signaling is not required for the in vivo or in vitro development of CD4+ lymphocytes with a Th2 cytokine profile.

The concept that IL-4 is the primary signal for Th2 lymphocyte differentiation has recently been put in doubt by studies in which the production of Th2-associated cytokines was detected in mice deficient in IL-4 synthesis or IL-4R triggering. In this study, we formally demonstrate by single cell analysis that CD4+ lymphocytes with a classical Th2 phenotype (IL-4+, IL-5+, IFN-gamma-, IL-2-) develop in significant numbers in helminth-infected mice deficient in either IL-4R alpha-chain or Stat6. While an expanded population of Th1 (IL-4-, IL-5-, IFN-gamma+, IL-2+) lymphocytes was observed in the same animals, surprisingly, cells with a mixed Th0 cytokine pattern were rare. The cytokine production phenotypes of the Th1 and Th2 subpopulations generated in infected Stat6-deficient mice were unaffected by in vitro neutralization of endogenous IL-4 or IFN-gamma. Nevertheless, while addition of exogenous rIL-12 resulted in transitory IFN-gamma production by Th2 lymphocytes from both wild-type and Stat6-deficient mice, IL-4 synthesis was preserved in the former, but temporarily ablated in the latter cells. Importantly, IL-4+ IFN-gamma- and IL-4- IFN-gamma+ populations similar to those arising in helminth-infected Stat6-deficient mice could also be generated in vitro by repetitive polyclonal stimulation of CD4+CD62Lhigh lymphocytes from uninfected mice of the same strain. Together, the results of these single cell analysis experiments demonstrate that IL-4R/Stat6 signaling, while influencing the final frequency of Th2 lymphocytes, is not essential for Th2 cell development, and suggest that this pathway has a previously unrecognized function in stabilizing Th2 populations once they have emerged.