T regulatory cells: aid or hindrance in the clearance of disease?

A splice of life: the discovery, function, and clinical implications of FOXP3 isoforms in autoimmune disease

Regulatory T cells (Tregs) are a specialized subset of CD4+ T cells essential for the maintenance of immune homeostasis and prevention of autoimmunity. Treg lineage and functions are programmed by the X-chromosome encoded transcription factor forkhead box P3 (FOXP3). In humans, multiple FOXP3 isoforms are generated through alternative splicing. A full-length isoform containing all coding exons (FOXP3-FL) and a version lacking the second exon (FOXP3-ΔE2) are the predominant FOXP3 isoforms. Additionally, there are two minor isoforms lacking either exon 7 (FOXP3-ΔE7) and both exons 2 and 7 (FOXP3-ΔE2ΔE7). Although healthy humans express approximately equal levels of the FOXP3-FL and FOXP3-ΔE2 isoforms, sole expression of FOXP3-ΔE2 results in the development of a systemic autoimmune disease that resembles immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome. These clinical observations strongly suggest functional defects in suppression by Tregs programmed by the FOXP3-ΔE2 isoform. Work from the past two decades has provided phenotypic and functional evidence of differences between Tregs programmed by the FOXP3-FL, FOXP3-ΔE2, and FOXP3-ΔE7 isoforms. In this review, we discuss the discovery of the FOXP3 isoforms, differences in the phenotype and function of Tregs programmed by different FOXP3 isoforms, and the role that these isoforms are known to play in autoimmunity.

Dysregulation of T cell response in the pathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD), comprised of Crohn's disease (CD) and ulcerative colitis (UC), are gut inflammatory diseases that were earlier prevalent in the Western Hemisphere but now are on the rise in the East, with India standing second highest in the incidence rate in the world. Inflammation in IBD is a cause of dysregulated immune response, wherein helper T (Th) cell subsets and their cytokines play a major role in the pathogenesis of IBD. In addition, gut microbiota, environmental factors such as dietary factors and host genetics influence the outcome and severity of IBD. Dysregulation between effector and regulatory T cells drives gut inflammation, as effector T cells like Th1, Th17 and Th9 subsets Th cell lineages were found to be increased in IBD patients. In this review, we attempted to discuss the role of different Th cell subsets together with other T cells like CD8+ T cells, NKT and γδT cells in the outcome of gut inflammation in IBD. We also highlighted the potential therapeutic candidates for IBD.

MEK-inhibitor treatment reduces the induction of regulatory T cells in mice after influenza A virus infection

Regulatory T cells (Tregs) play a crucial and complex role in balancing the immune response to viral infection. Primarily, they serve to regulate the immune response by limiting the expression of proinflammatory cytokines, reducing inflammation in infected tissue, and limiting virus-specific T cell responses. But excessive activity of Tregs can also be detrimental and hinder the ability to effectively clear viral infection, leading to prolonged disease and potential worsening of disease severity. Not much is known about the impact of Tregs during severe influenza. In the present study, we show that CD4+/CD25+FoxP3+ Tregs are strongly involved in disease progression during influenza A virus (IAV) infection in mice. By comparing sublethal with lethal dose infection in vivo, we found that not the viral load but an increased number of CD4+/CD25+FoxP3+ Tregs may impair the immune response by suppressing virus specific CD8+ T cells and favors disease progression. Moreover, the transfer of induced Tregs into mice with mild disease symptoms had a negative and prolonged effect on disease outcome, emphasizing their importance for pathogenesis. Furthermore, treatment with MEK-inhibitors resulted in a significant reduction of induced Tregs in vitro and in vivo and positively influenced the progression of the disease. Our results demonstrate that CD4+/CD25+FoxP3+ Tregs are involved in the pathogenesis of severe influenza and indicate the potential of the MEK-inhibitor zapnometinib to modulate CD4+/CD25+FoxP3+ Tregs. Thus, making MEK-inhibitors even more promising for the treatment of severe influenza virus infections.

Making a Monkey out of Human Immunodeficiency Virus/Simian Immunodeficiency Virus Pathogenesis: Immune Cell Depletion Experiments as a Tool to Understand the Immune Correlates of Protection and Pathogenicity in HIV Infection

Understanding the underlying mechanisms of HIV pathogenesis is critical for designing successful HIV vaccines and cure strategies. However, achieving this goal is complicated by the virus's direct interactions with immune cells, the induction of persistent reservoirs in the immune system cells, and multiple strategies developed by the virus for immune evasion. Meanwhile, HIV and SIV infections induce a pandysfunction of the immune cell populations, making it difficult to untangle the various concurrent mechanisms of HIV pathogenesis. Over the years, one of the most successful approaches for dissecting the immune correlates of protection in HIV/SIV infection has been the in vivo depletion of various immune cell populations and assessment of the impact of these depletions on the outcome of infection in non-human primate models. Here, we present a detailed analysis of the strategies and results of manipulating SIV pathogenesis through in vivo depletions of key immune cells populations. Although each of these methods has its limitations, they have all contributed to our understanding of key pathogenic pathways in HIV/SIV infection.

c-Jun N-terminal kinase 1 defective CD4+CD25+FoxP3+ cells prolong islet allograft survival in diabetic mice

CD4+CD25+FoxP3+ cells (Tregs) inhibit inflammatory immune responses to allografts. Here, we found that co-transplantation of allogeneic pancreatic islets with Tregs that are defective in c-Jun N-terminal kinase 1 (JNK1) signaling prolongs islet allograft survival in the liver parenchyma of chemically induced diabetic mice (CDM). Adoptively transferred JNK1^−/− but not wild-type (WT) Tregs survive longer in the liver parenchyma of CDM. JNK1^−/− Tregs are resistant to apoptosis and express anti-apoptotic molecules. JNK1^−/− Tregs express higher levels of lymphocyte activation gene-3 molecule (LAG-3) on their surface and produce higher amounts of the anti-inflammatory cytokine interleukin (IL)-10 compared with WT Tregs. JNK1^−/− Tregs inhibit liver alloimmune responses more efficiently than WT Tregs. JNK1^−/− but not WT Tregs are able to inhibit IL-17 and IL-21 production through enhanced LAG-3 expression and IL-10 production. Our study identifies a novel role of JNK1 signaling in Tregs that enhances islet allograft survival in the liver parenchyma of CDM.

Genetic, Immunologic, and Environmental Basis of Sarcoidosis

Sarcoidosis is a multisystem disease with tremendous heterogeneity in disease manifestations, severity, and clinical course that varies among different ethnic and racial groups. To better understand this disease and to improve the outcomes of patients, a National Heart, Lung, and Blood Institute workshop was convened to assess the current state of knowledge, gaps, and research needs across the clinical, genetic, environmental, and immunologic arenas. We also explored to what extent the interplay of the genetic, environmental, and immunologic factors could explain the different phenotypes and outcomes of patients with sarcoidosis, including the chronic phenotypes that have the greatest healthcare burden. The potential use of current genetic, epigenetic, and immunologic tools along with study approaches that integrate environmental exposures and precise clinical phenotyping were also explored. Finally, we made expert panel-based consensus recommendations for research approaches and priorities to improve our understanding of the effect of these factors on the health outcomes in sarcoidosis.

Immunological effects of vaccines combined with granulocyte colony-stimulating factor on a murine WEHI-3 leukemia model

Granulocyte colony-stimulating factor (G-CSF) mobilizes regulatory T cells (Tregs) from bone marrow into the peripheral blood, by reducing the expression of stromal cell-derived factor-1α (SDF-1α). However, G-CSF has rarely been studied in acute myeloid leukemia (AML) immunotherapy. The present study performed a Transwell migration assay in vitro to determine the contribution of SDF-1α to the migration of leukemia cells, and the effects of G-CSF were evaluated. The effects of G-CSF on SDF-1α and Tregs in the AML microenvironment were examined, by employing a WEHI-3-grafted BALB/c mouse AML model (AML-M4). It is evident that G-CSF reversed immunosuppression of the AML microenvironment by reducing SDF-1α in bone marrow and elevating Tregs in the peripheral blood in in vivo studies. Furthermore, AML mice treated with vaccines combined with G-CSF achieved a longer survival time than those treated with vaccines without G-CSF, showing the efficiency of the regimen. The present study demonstrates the effects of G-CSF on the mobilization of leukemia cells and Tregs into the peripheral blood. In addition, immunotherapy with G-CSF priming represents a promising therapeutic strategy of targeting the immunosuppression.

Prophylactic and therapeutic modulation of innate and adaptive immunity against mucosal infection of herpes simplex virus

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) are the most common cause of genital ulceration in humans worldwide. Typically, HSV-1 and 2 infections via mucosal route result in a lifelong latent infection after peripheral replication in mucosal tissues, thereby providing potential transmission to neighbor hosts in response to reactivation. To break the transmission cycle, immunoprophylactics and therapeutic strategies must be focused on prevention of infection or reduction of infectivity at mucosal sites. Currently, our understanding of the immune responses against mucosal infection of HSV remains intricate and involves a balance between innate signaling pathways and the adaptive immune responses. Numerous studies have demonstrated that HSV mucosal infection induces type I interferons (IFN) via recognition of Toll-like receptors (TLRs) and activates multiple immune cell populations, including NK cells, conventional dendritic cells (DCs), and plasmacytoid DCs. This innate immune response is required not only for the early control of viral replication at mucosal sites, but also for establishing adaptive immune responses against HSV antigens. Although the contribution of humoral immune response is controversial, CD4(+) Th1 T cells producing IFN-γ are believed to play an important role in eradicating virus from the hosts. In addition, the recent experimental successes of immunoprophylactic and therapeutic compounds that enhance resistance and/or reduce viral burden at mucosal sites have accumulated. This review focuses on attempts to modulate innate and adaptive immunity against HSV mucosal infection for the development of prophylactic and therapeutic strategies. Notably, cells involved in innate immune regulations appear to shape adaptive immune responses. Thus, we summarized the current evidence of various immune mediators in response to mucosal HSV infection, focusing on the importance of innate immune responses.

Association of two clones allows for optimal detection of human FOXP3

FOXP3 is a key transcription factor expressed by regulatory T cells (Treg cells). However, differences in staining and analysis protocols have led to conflicting results. Moreover, the transient upregulation of FOXP3 that follows activation in non-Treg cells renders the interpretation of FOXP3 data more difficult in humans than in mice. Human peripheral blood mononuclear cells (PBMCs), isolated CD25(-) or CD25(+)CD4(+) T cells were stained with three different anti-FOXP3 clones (PCH101, 206D, and 259D) alone or in combination, and using different permeabilization methods. FOXP3 expression was evaluated following T cell activation by several pathways. Gating based on a population that did not express FOXP3 (such as CD3(-)CD4(-) T cells) allowed for the optimal characterization of Treg cells. The 206D clone detected a lower percentage of cells than PCH101 or 259D. In contrast, 259D stained a population of activated T cells that PCH101 did not. Staining with two clones together consistently increased the proportion of FOXP3(+) cells. However, it is likely that only the double positive cells are Treg cells, as they expressed the highest CD25 and lowest CD127 levels. Our results emphasize that the choice of staining protocol leads to very different results concerning the frequency of Treg cells in humans. A more consistent identification of these cells will improve the knowledge of their biology, particularly during disease processes.

Regulatory T cells and EBV associated malignancies

It has been shown that the T-regulatory cells (Tregs) not only play a key role in the establishment and maintenance of peripheral tolerance to prevent the autoimmune disease, but also inhibit the anti-tumor immunity. Recently, many studies have demonstrated that cytotoxicity T cells (CTL) can control the growth of EBV-positive tumor cells in vitro, including Hodgkin's lymphoma (HL), nasopharyngeal carcinoma, posttransplantation lymphoproliferative disorders (PTLD), depending on the large mount of EBV antigens presented by MHC molecules on the surface of these malignant cells. However, limited benefit of CTL adoptive immunotherapy has been reported in the treatment of EBV positive HL and NPC, and Tregs are regarded as a critical hurdle in this issue. In the present review, we discuss the correlation of EBV antigens expression in the tumor cells and the induction of Tregs in tumor microenvironment. Treg subsets and its possible mechanism to attenuate the anti-tumor immunity in EBV associated malignancies are also discussed, following by the possible strategies of targeting Tregs in the future immunotherapy for EBV positive cancers.

Inflammatory markers in depression

PURPOSE OF REVIEW

To provide a critical update of the literature linking depression and inflammation, together with possible underlying mechanisms and longer term risk of cardiovascular disease.

RECENT FINDINGS

The current literature lends further support to the view that major depression is associated with a proinflammatory response, as indexed by elevation in C-reactive protein and cytokines such as interleukin 6 and tumour necrosis factor-alpha. Antidepressants suppress the inflammatory response, whereas electroconvulsive therapy acutely increases proinflammatory cytokine levels. Most, though not all, studies support a link between depression, inflammation and cardiovascular events.

SUMMARY

Depression is an inflammatory state that may increase the risk of cardiac disease. Whether or not the immune system is an appropriate target for antidepressant development has yet to be established.

Cutting edge: Experimentally induced immune activation in natural hosts of simian immunodeficiency virus induces significant increases in viral replication and CD4+ T cell depletion

Chronically SIVagm-infected African green monkeys (AGMs) have a remarkably stable nonpathogenic disease course, with levels of immune activation in chronic SIVagm infection similar to those observed in uninfected monkeys and with stable viral loads for long periods of time. In vivo administration of LPS or an IL-2/diphtheria toxin fusion protein (Ontak) to chronically SIVagm-infected AGMs triggered increases in immune activation and subsequently of viral replication and depletion of intestinal CD4(+) T cells. Our study indicates that circulating microbial products can increase viral replication by inducing immune activation and increasing the number of viral target cells, thus demonstrating that immune activation and T cell proliferation are key factors in AIDS pathogenesis.