Jyoti Das

A critical role for NF-kappa B in GATA3 expression and TH2 differentiation in allergic airway inflammation.

The transcription factor GATA-3 is expressed in T helper 2 (TH2) but not TH1 cells and plays a critical role in TH2 differentiation and allergic airway inflammation in vivo. Mice that lack the p50 subunit of nuclear factor κB (NF-κB) are unable to mount airway eosinophilic inflammation. We show here that this is not due to defects in TH2 cell recruitment but due to the inability of the p50−/− mice to produce interleukin 4 (IL-4), IL-5 and IL-13: cytokines that play distinct roles in asthma pathogenesis. CD4+ T cells from p50−/− mice failed to induce Gata3 expression under TH2-differentiating conditions but showed unimpaired T-bet expression and interferon γ (IFN-γ) production under TH1-differentiating conditions. Inhibition of NF-κB activity prevented GATA-3 expression and TH2 cytokine production in developing, but not committed, TH2 cells. Our studies provide a molecular basis for the need for both T cell receptor and cytokine signaling for GATA-3 expression and, in turn, TH2 differentiation.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and T-cell responses: what we do and don't know

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important hematopoietic growth factor and immune modulator. GM-CSF also has profound effects on the functional activities of various circulating leukocytes. It is produced by a variety of cell types including T cells, macrophages, endothelial cells and fibroblasts upon receiving immune stimuli. Although GM-CSF is produced locally, it can act in a paracrine fashion to recruit circulating neutrophils, monocytes and lymphocytes to enhance their functions in host defense. Recent intensive investigations are centered on the application of GM-CSF as an immune adjuvant for its ability to increase dendritic cell (DC) maturation and function as well as macrophage activity. It is used clinically to treat neutropenia in cancer patients undergoing chemotherapy, in AIDS patients during therapy, and in patients after bone marrow transplantation. Interestingly, the hematopoietic system of GM-CSF-deficient mice appears to be normal; the most significant changes are in some specific T cell responses. Although molecular cloning of GM-CSF was carried out using cDNA library of T cells and it is well known that the T cells produce GM-CSF after activation, there is a lack of systematic investigation of this cytokine in production by T cells and its effect on T cell function. In this article, we will focus mainly on the immunobiology of GM-CSF in T cells.

An important regulatory role for CD4+CD8αα T cells in the intestinal epithelial layer in the prevention of inflammatory bowel disease

The normal immunoregulatory mechanisms that maintain homeostasis in the intestinal mucosa, despite continuous provocation by environmental antigens, are jeopardized in inflammatory bowel diseases. Although previous studies have suggested that intestinal intraepithelial lymphocytes prevent spontaneous intestinal inflammation, there is limited knowledge about the characteristics of regulatory cells in the intestinal intraepithelial lymphocytes population. Here we show that CD4+CD8αα+ double-positive cells present in the intestinal intraepithelial lymphocytes population can suppress T helper 1-induced intestinal inflammation in an IL-10-dependent fashion. CD4+ T cells stimulated along the Th2 but not the Th1 lineage, when transferred to RAG-1−/− mice, acquire CD8αα expression on reaching the intestinal epithelium, and on arrival there, augment their production of IL-10. We show that a precursor CD4+ T cell after limited, but not repeated, stimulation by IL-4 is able to become a double-positive-regulatory cell on exposure to the intestinal microenvironment in mice. Both CD8αα acquisition and IL-10 production depend critically on the NF-κB-GATA-3-axis that we have previously shown is essential for differentiation to the Th2 phenotype and for the induction of airway inflammation. Our studies identify a mechanism for the generation of regulatory T cells in the intestine that may play an important role in controlling inflammatory bowel disease.

The role of activation-induced cell death in the differentiation of T-helper-cell subsets

Activation-induced cell death (AICD) has been demonstrated in T-cell hybridomas, immature thymocytes, and activated mature T cells. However, the molecular mechanisms of AICD and its physiological role in T-helper-cell differentiation remain uncertain. Recently, we have shown that Th1 and Th2 cells have distinct mechanisms of AICD. Our findings suggest that signaling from cytokines initiates the differentiation program, but that the selective action of death effectors determines the fate of differentiating T-helper cells, and thus, the ultimate balance between T-helper subpopulations. Among T cells, activation-induced expression of the tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is observed exclusively in Th2 clones and primary T-helper cells differentiated under Th2 conditions, while the expression of CD95L (Fas ligand) occurs mainly in Th1 cells. Furthermore, Th1 cells are more susceptible than Th2 cells to apoptosis induced through either TRAIL or CD95L, and radiolabeled Th1 cells can be induced into apoptosis via fratricide by both Th1 and Th2 cells, while Th2 cells are spared. The pan-caspase inhibitor, z-VAD, prevents AICD in Th1 cells, but not Th2 cells, indicating different mechanisms of AICD in each T-helper subtype. Antibody blockade of TRAIL and CD95L significantly boosts interferon-γ (IFN-γ) production in vitro. Also, young mice with mutant CD95 (MRL/MpJ-lpr/lpr) have a stronger Th1 response to ovalbumin immunization than do controls. We conclude that apoptosis mediated by CD95L and TRAIL is critical in the selective removal of differentiating T helper cells.

Natural killer T cells and CD8+ T cells are dispensable for T cell-dependent allergic airway inflammation.

Natural killer T cells and CD8 + T cells are dispensable for T cell–dependent allergic airway inflammation

Inflammatory bowel disease requires the interplay between innate and adaptive immune signals

Inflammatory bowl disease (IBD) is a type 1 T helper cell (Th1)-mediated autoimmune disease. Various studies have revealed that environmental pathogens also play a significant role in the initiation and progression of this disease. Interestingly, the pathogenesis of IBD has been shown to be related to nitric oxide (NO) released from innate immune cells. Although NO is known to be highly toxic to the gut epithelia, there is very little information about the regulation of NO production, One major question in the etiology of IBD is how Th1 cells and pathogens interact in the induction of IBD. In present study, we focused on the regulation of NO. We show that macrophages require both interferon-γ (IFN-γ)-mediated and TLR4-mediated signals for the production of NO, which causes inflammation in the intestine and subsequently IBD. Thus, IBD is the result of concerted actions of innate immune signals, such as the binding of LPS to TLR-4, and adaptive immune signals, such as IFN-γ produced by Th1 cells.

Transforming growth factor-β protein inversely regulates in vivo differentiation of interleukin-17 (IL-17)-producing CD4+ and CD8+ T cells.

Background: In vitro TGF-β differentiates Th17 and Tc17 cells, but TGF-βRIIDN mice display multiorgan autoimmune disorders. Results: CD4+T cells from TGF-βRIIDN mice are resistant to Th17 cell differentiation, whereas CD8+T cells acquire IL-17-producing phenotype, and IL-17 neutralization or depletion inhibited inflammation in TGF-βRIIDN mice. Conclusion: Tc17 cell differentiations in vivo are distinct from Tc17 cell differentiations in vitro. Significance: The Tc17 cell differentiation program is unique to Th17. TGF-β is a pleiotropic cytokine that predominantly exerts inhibitory functions in the immune system. Unexpectedly, the in vitro differentiation of both Th17 and Tc17 cells requires TGF-β. However, animals that are impaired in TGF-β signaling (TGF-βRIIDN mice) display multiorgan autoimmune disorders. Here we show that CD4+ T cells from TGF-βRIIDN mice are resistant to Th17 cell differentiation and, paradoxically, that CD8+ T cells from these animals spontaneously acquire an IL-17-producing phenotype. Neutralization of IL-17 or depletion of CD8+ T cells dramatically inhibited inflammation in TGF-βRIIDN mice. Therefore, the absence of TGF-β triggers spontaneous differentiation of IL-17-producing CD8+ T cells, suggesting that the in vivo and in vitro conditions that promote the differentiation of IL-17-producing CD8+ T cells are distinct.

CD4+ T Cell-derived Novel Peptide Thp5 Induces Interleukin-4 Production in CD4+ T Cells to Direct T Helper 2 Cell Differentiation

Background: CD4+ T cells produce IL-4 that drives Th2 cell differentiation. Early production of IL-4 in naïve T cells leads to Th2 cell differentiation. Results: Thp5, a novel peptide, regulates IL-4 production in early activated CD4+ T cells. Conclusion: Early activated CD4+ T cells produce Thp5, which plays a critical role in the differentiation of Th2 cells. Significance: Thp5 acts as an important determinant of Th2 cell differentiation during early T cell activation. The differentiation of naïve CD4+ T cells into T helper 2 (Th2) cells requires production of the cytokine IL-4 in the local microenvironment. It is evident that naïve/quiescently activated CD4+ T cells produce the IL-4 that drives Th2 cell differentiation. Because early production of IL-4 in naïve T cells leads to preferential Th2 cell differentiation, this process needs to be tightly regulated so as to avoid catastrophic and misdirected Th2 cell differentiation. Here, we show that Thp5, a novel peptide with structural similarity to vasoactive intestinal peptide, regulates production of early IL-4 in newly activated CD4+ T cells. Induction of IL-4 in CD4+ T cells by Thp5 is independent of the transcription factor STAT6 but dependent on ERK1/2 signaling. Furthermore, cytokines (IL-12 and TGF-β) that promote the differentiation of Th1 or Th17 cells inhibit Thp5 induction, thus suppressing Th2 cell differentiation. We further showed that Thp5 enhances Th2 responses and exacerbates allergic airway inflammation in mice. Taken together, our findings reveal that early activated CD4+ T cells produce Thp5, which plays a critical role as a molecular switch in the differentiation of Th cells, biasing the response toward the Th2 cell phenotype.

Pivotal roles of CD8+ T cells restricted by MHC class I–like molecules in autoimmune diseases

Unlike T cells restricted by major histocompatibility complex (MHC) class Ia or class II molecules, T cells restricted by MHC class I–like molecules demonstrate properties of both innate and adaptive immunity and are therefore considered innate-like lymphocytes (ILLs). ILLs are believed to have immunoregulatory functions, but their roles in autoimmunity and defense against infections remain elusive. To study the properties of ILLs, we generated mice expressing only MHC class I–like molecules by crossing CIITA−/− with Kb−/−Db−/− mice. Surprisingly, these mice developed a lymphoproliferative syndrome and autoimmunity, most notably inflammatory bowel disease (IBD) and insulitis. The CD8+ ILLs in these mice exhibit a constitutively activated phenotype, and depletion of these cells abolished the autoimmune disorders. In addition, adoptive transfer of CD8+ ILLs from Kb−/−Db−/−CIITA−/− mice to Rag-1−/−pfn−/− mice also resulted in IBD and insulitis. These findings provide direct evidence that CD8+ ILLs are sufficient to initiate and mediate autoimmune diseases.

Prostanoid Receptor 2 Signaling Protects T Helper 2 Cells from BALB/c Mice against Activation-induced Cell Death

Background: The mechanism by which BALB/c mice exhibit a propensity to induce T helper 2 (Th2) responses and allergic diseases is unknown. Results: Prostaglandin endoperoxide E2 (PGE2) prevents activation-induced cell death in Th2 cells of BALB/c mice via the E-prostanoid 2 (EP2) receptor and is dependent on granzyme B. Conclusion: Signaling of PGE2 through EP2 promotes Th2 immune responses. Significance: EP2 can be targeted as a therapeutic modality for Th2-mediated diseases. T helper 2 (Th2) cells play a central role in the progression of many diseases such as allergic airway inflammation, autoimmune diseases, and infections caused by intracellular pathogens. Consequently, animals such as BALB/c mice, which exhibit a propensity for generating Th2 responses, are susceptible to allergic airway inflammation, type-II autoimmune diseases, and various infections induced by intracellular pathogens, namely, Leishmania. In contrast, C3H/OuJ mice have a tendency for generating T helper 1 (Th1) responses and show resistance to these diseases. Here, we show that prostaglandin endoperoxide E2 selectively inhibits activation-induced cell death of Th2 cells by signaling through its receptor E-prostanoid receptor 2 (EP2). Consequently, Th2 cells derived from BALB/c mice expressed very high levels of EP2. On the other hand, Th2 cells derived from C3H/OuJ mice expressed very low levels of EP2, which failed to support the survival of Th2 cells. Furthermore, we found that this effect of EP2 on Th2 cells from BALB/c mice was executed by a granzyme B-mediated mechanism. EP2 belongs to a group of G-protein-coupled receptors that are amenable to therapeutic targeting. Our findings therefore identify EP2 as a promising target for small molecule-directed immunomodulation.