IRF4 at the crossroads of effector T-cell fate decision

Roles of the tacrolimus-dependent transcription factor IRF4 in acute rejection after liver transplantation

Acute rejection is a serious and life-threatening complication of liver transplantation (LTx). Tacrolimus (TAC) is a potent immunosuppressant used in experimental and clinical transplantation. Interferon regulatory factor 4 (IRF4) plays key roles as a transcription factor in the immune response. This study explored the role of IRF4 in acute rejection after LTx using TAC treatment. Here, LTx was performed in DA (RT1(n)) and Lewis (LEW) (RT1(l)) rats. The recipients were immunosuppressed with TAC (1.5mg/kg/day subcutaneously) or saline. Liver grafts were harvested 1, 3, 5, 7, and 10 days after LTx for histology, immunohistochemistry, western blotting and real-time PCR. Splenic mononuclear cells were activated with different doses of TAC. The nuclear factor of activated T cells (NFAT) signal pathway and CD4+ T subset-related transcription factors were assessed. The results showed that TAC treatment prolonged the survival of liver allografts in recipients, significantly attenuated hepatic tissue injury and improved liver function. IRF4 expression in grafts was down-regulated after TAC treatment. TAC inhibited the expression of IRF4, NFAT, Foxp3 and RORγt in splenic mononuclear cells in vitro. In conclusions, our studies showed that TAC attenuated acute rejection responses after LTx. This attenuation might depend on the TAC-NFAT-IRF4 signal pathway, which is crucial for the function of T helper subsets (Treg and Th17 cells) in acute rejection after LTx. These findings contribute to our understanding of the immune pharmacological mechanism of TAC to prevent rejection in LTx rats.

T helper 2 (Th2) cell differentiation, type 2 innate lymphoid cell (ILC2) development and regulation of interleukin-4 (IL-4) and IL-13 production

Interleukin-4 (IL-4), IL-5 and IL-13, the signature cytokines that are produced during type 2 immune responses, are critical for protective immunity against infections of extracellular parasites and are responsible for asthma and many other allergic inflammatory diseases. Although many immune cell types within the myeloid lineage compartment including basophils, eosinophils and mast cells are capable of producing at least one of these cytokines, the production of these "type 2 immune response-related" cytokines by lymphoid lineages, CD4 T helper 2 (Th2) cells and type 2 innate lymphoid cells (ILC2s) in particular, are the central events during type 2 immune responses. In this review, I will focus on the signaling pathways and key molecules that determine the differentiation of naïve CD4 T cells into Th2 cells, and how the expression of Th2 cytokines, especially IL-4 and IL-13, is regulated in Th2 cells. The similarities and differences in the differentiation of Th2 cells, IL-4-producing T follicular helper (Tfh) cells and ILC2s as well as their relationships will also be discussed.

Regulatory plasma cells

B cells can regulate immunity negatively or positively. Identifying the B cell subsets mediating these antagonistic activities, and the molecular mechanisms governing their differentiation, might enable the development of novel approaches to target B cells therapeutically. The suppressive functions of B cells are primarily mediated through their production of interleukin (IL)-10 and IL-35. Recent studies have shown that distinct sets of IgM(+)CD19(+)CD138(hi) plasma cells were the major B cell subsets producing these cytokines in a regulatory manner in vivo during autoimmune and infectious diseases. This review summarizes current knowledge on these 'regulatory plasma cells', and discusses the emerging data showing that the mechanisms involved in their generation partly overlap with those controlling the differentiation of 'effector regulatory T cells'.

Tim-3 protects decidual stromal cells from toll-like receptor-mediated apoptosis and inflammatory reactions and promotes Th2 bias at the maternal-fetal interface

Toll-like receptors (TLRs) are important in mediating immune responses against various pathogens during pregnancy. However, uncontrolled TLR-triggered inflammation will endanger normal pregnancy, resulting in pregnancy loss. Therefore, maintenance of a moderate inflammatory response is crucial for successful pregnancy under conditions of infection. Here, we demonstrated significantly lowered expression of T-cell immunoglobulin and mucin domain 3 (Tim-3) in miscarried decidual stromal cells (DSCs), indicating that Tim-3 might play important roles in maintaining successful pregnancies. Activation of TLR signaling induced pro-inflammatory cytokine production and apoptosis of DSCs, which was accompanied by up-regulated Tim-3 expression. Tim-3, in turn, protected DSCs from TLR-mediated apoptosis in an ERK1/2 pathway-dependent manner. In addition, Tim-3 inhibited TLR signaling-induced inflammatory cytokine production by DSCs through suppressing NF-κB activation. Tim-3 increased production of T helper 2 (Th2)-type cytokines by DSCs and reversed the inhibitory effect of LPS on Th2 cytokine generation by up-regulation of interferon regulatory factor 4 expression. Tim-3 blockade abolished the effect of Tim-3 on the inflammatory response to LPS stimulation. Thus, Tim-3 signaling could represent a “self-control” mechanism in TLR-triggered inflammation during pregnancy. These findings identify Tim-3 as a key regulator of DSCs and suggest its potential as a target for the treatment of spontaneous abortion.

IL-17A-producing CD8(+)T cells as therapeutic targets in autoimmunity

INTRODUCTION

The involvement of IL-17-producing CD8(+)T cells (TC17) in various conditions, such as infection, cancer and autoimmune inflammation, has been documented in both humans and mice; however, TC17 cells have received only marginal attention.

AREAS COVERED

Here, we provide an overview of the cytokines, chemokines, and cytokine and chemokine receptors that characterize the murine and human TC17 cell phenotype. We also discuss signaling pathways, molecular interactions, and transcriptional and epigenetic events that contribute to TC17 differentiation and acquisition of effector functions. Heterogeneity and inherent phenotypic instability of TC17 cells were shown both in humans and murine models. Aberrant expression of TC17 cells was observed in many autoimmune conditions. Moreover, functional analysis demonstrated in vivo plasticity of TC17 cells may be a key feature of TC17 cell biology in autoimmune diseases.

EXPERT OPINION

Due to its important roles in inflammation and autoimmunity, TC17 cell pathway may have promise as a potential therapeutic target for autoimmune diseases. The strategies include the suppression of TC17 cell generation and migration and the blockade of TC17 cell instability and heterogeneity. TMP778 may open an avenue to novel therapeutic strategies.

Essential role of IRF4 and MYC signaling for survival of anaplastic large cell lymphoma

IRF4 regulates MYC expression in ALCL. ALCL survival depends on IRF4/MYC signaling.