Single-cell RNA sequencing unveils an IL-10-producing helper subset that sustains humoral immunity during persistent infection

Molecular switches for regulating the differentiation of inflammatory and IL-10-producing anti-inflammatory T-helper cells

CD4 T-helper (Th) cells secret a variety of inflammatory cytokines and play critical roles in host defense against invading foreign pathogens. On the other hand, uncontrolled inflammatory responses mediated by Th cells may result in tissue damage and inflammatory disorders including autoimmune and allergic diseases. Thus, the induction of anti-inflammatory cytokine expression becomes an important "brake" to repress and/or terminate aberrant and/or unnecessary immune responses. Interleukin-10 (IL-10) is one of the most important anti-inflammatory cytokines to limit inflammatory Th cells and immunopathology and to maintain tissue homeostasis. Many studies have indicated that Th cells can be a major source of IL-10 under specific conditions both in mouse and human and that extracellular signals and cell intrinsic molecular switches are required to turn on and off Il10 expression in different Th cells. In this review, we will highlight the recent findings that have enhanced our understanding on the mechanisms of IL-10 induction in distinct Th-cell subsets, including Th1, Th2, and Th17 cells, as well as the importance of these IL-10-producing anti-inflammatory Th cells in immunity and inflammation.

Molecular Signatures of Dengue Virus-Specific IL-10/IFN-γ Co-producing CD4 T Cells and Their Association with Dengue Disease

Dengue virus (DENV) can cause diseases ranging from dengue fever (DF) to more severe dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Whether antiviral T cells contribute to the protection against or pathogenesis of severe disease is not well defined. Here, we identified antigen-specific IL-10+IFN-γ+ double-positive (DP) CD4 T cells during acute DENV infection. While the transcriptomic signatures of DP cells partially overlapped with those of cytotoxic and type 1 regulatory CD4 T cells, the majority of them were non-cytotoxic/Tr1 and included IL21, IL22, CD109, and CCR1. Although we observed a higher frequency of DP cells in DHF, the transcriptomic profile of DP cells was similar in DF and DHF, suggesting that DHF is not associated with the altered phenotypic or functional attributes of DP cells. Overall, this study revealed a DENV-specific DP cell subset in patients with acute dengue disease and argues against altered DP cells as a determinant of DHF.

An overview of T follicular cells in transplantation: spotlight on their clinical significance

Introduction: For late stage organ failure patients, transplantation is the best option to increase life expectancy with a superior quality of life. Unfortunately, after transplantation many patients are at risk of cellular and antibody-mediated rejection (ABMR). The latter is initiated by donor specific antibodies (DSA) which depend on the actions of B cells, T follicular helper (Tfh) cells and T follicular regulatory (Tfr) cells that are present in the germinal center of lymphoid organs.Areas covered: In this overview paper, we discuss the biology and function of Tfh and Tfr cells in lymphoid tissues, transplanted organs and their circulating counterparts. We report on their relevance to alloimmunity and on the effects of immunosuppressive drugs on these immunocompetent cell populations.Expert opinion: Growing knowledge about the actions of Tfh and Tfr allows for a better understanding of the immunological mechanisms of ABMR after organ transplantation. This understanding feeds the hypothesis that immunosuppressive drugs targeting the actions of Tfh cells have huge therapeutic potential. This new concept in the treatment of the humoral rejection response will improve graft and patient survival after organ transplantation.

Title: IL-10-producing T cells and their dual functions

Interleukin (IL)-10 is considered a prototypical anti-inflammatory cytokine, which significantly contributes to the maintenance and reestablishment of immune homeostasis. However, this classical view fails to fully describe the pleiotropic roles of IL-10. Indeed, IL-10 can also promote immune responses, e.g. by supporting B-cell and CD8⁺ T-cell activation. The reasons for these seemingly opposing functions are unclear to a large extent. Recent and previous studies suggest that the cellular source and the microenvironment impact the function of IL-10. However, studies addressing the mechanisms which determine whether IL-10 promotes inflammation or controls it have just begun. This review first summarizes the recent findings on the heterogeneity of IL-10 producing T cells and their impact on the target cells. Finally, we will propose two possible explanations for the dual functions of IL-10.

IL-12 signaling drives the differentiation and function of a TH1-derived TFH1-like cell population

CD4⁺ T follicular helper (T_FH) cells provide help to B cells and promote antibody-mediated immune responses. Increasing evidence supports the existence of T_FH populations that secrete cytokines typically associated with the effector functions of other CD4⁺ T cell subsets. These include T helper 1 (T_H1)-biased T_FH (T_FH1) cells that have recognized roles in both immune responses to pathogens and also the pathogenesis of autoimmune disease. Given their apparent importance to human health, there is interest in understanding the mechanisms that regulate T_FH1 cell formation and function. However, their origin and the molecular requirements for their differentiation are unclear. Here, we describe a population of murine T_H1-derived, T_FH1-like cells that express the chemokine receptor Cxcr3 and produce both the T_H1 cytokine interferon-γ and the T_FH-associated cytokine interleukin-21 (IL-21). Furthermore, these T_FH1-like cells promote B cell activation and antibody production at levels indistinguishable from conventional IL-6-derived T_FH-like cells. Regarding their regulatory requirements, we find that IL-12 signaling is necessary for the differentiation and function of this T_FH1-like cell population. Specifically, IL-12-dependent activation of STAT4, and unexpectedly STAT3, promotes increased expression of IL-21 and the T_FH lineage-defining transcription factor Bcl-6 in T_FH1-like cells. Taken together, these findings provide insight into the potential origin and differentiation requirements of T_FH1 cells.

Striking a Balance-Cellular and Molecular Drivers of Memory T Cell Development and Responses to Chronic Stimulation

Effective adaptive immune responses are characterized by stages of development and maturation of T and B cell populations that respond to disturbances in the host homeostasis in cases of both infections and cancer. For the T cell compartment, this begins with recognition of specific peptides by naïve, antigen-inexperienced T cells that results in their activation, proliferation, and differentiation, which generates an effector population that clears the antigen. Loss of stimulation eventually returns the host to a homeostatic state, with a heterogeneous memory T cell population that persists in the absence of antigen and is primed for rapid responses to a repeat antigen exposure. However, in chronic infections and cancers, continued antigen persistence impedes a successful adaptive immune response and the formation of a stereotypical memory population of T cells is compromised. With repeated antigen stimulation, responding T cells proceed down an altered path of differentiation that allows for antigen persistence, but much less is known regarding the heterogeneity of these cells and the extent to which they can become “memory-like,” with a capacity for self-renewal and recall responses that are characteristic of bona fide memory cells. This review focuses on the differentiation of CD4⁺ and CD8⁺ T cells in the context of chronic antigen stimulation, highlighting the central observations in both human and mouse studies regarding the differentiation of memory or “memory-like” T cells. The importance of both the cellular and molecular drivers of memory T cell development are emphasized to better understand the consequences of persisting antigen on T cell fates. Integrating what is known and is common across model systems and patients can instruct future studies aimed at further understanding T cell differentiation and development, with the goal of developing novel methods to direct T cells toward the generation of effective memory populations.

The single-cell sequencing: new developments and medical applications

Single-cell sequencing technologies can be used to detect the genome, transcriptome and other multi-omics of single cells. They can show the differences and evolutionary relationships of various cells. This review introduces the latest advances in single-cell sequencing technologies and their applications in oncology, microbiology, neurology, reproduction, immunology, digestive and urinary systems, highlighting the important role that single-cell sequencing techniques play in these areas.

Percutaneous sensitization is limited by in situ inhibition of cutaneous dendritic cell migration through skin-resident regulatory T cells

BACKGROUND

Percutaneous sensitization is associated with various allergic diseases, including asthma and food allergies. However, the immunologic mechanisms underlying how the skin regulates percutaneous sensitization are still unclear.

OBJECTIVE

We aimed to investigate whether and how CD4⁺Foxp3⁺ regulatory T (Treg) cells residing in the skin regulate percutaneous sensitization in the skin.

METHODS

Selective reduction of numbers of cutaneous Treg cells was achieved by means of intradermal injection of diphtheria toxin into the ear skin of Foxp3^DTR mice, in which Treg cells specifically express the diphtheria toxin receptor fused with green fluorescent protein.

RESULTS

Thirty percent to 40% of cutaneous Treg cells were capable of IL-10 production in both mice and human subjects. Selective reduction of cutaneous Treg cells at the sensitization site promoted migration of antigen-bearing dendritic cells (DCs) to the draining lymph nodes (dLNs). Accordingly, sensitization through the skin with reduced numbers of Treg cells led to enhanced antigen-specific immune responses in the dLNs, including both effector T-cell differentiation and T cell-dependent B-cell responses, such as the development of germinal center B cells expressing IgG₁ and IgE. Furthermore, antigen-bearing cutaneous DC migration was enhanced in mice with IL-10 deficiency restricted to the cutaneous Treg cell compartment, suggesting an important role of cutaneous IL-10⁺ Treg cells in limiting percutaneous sensitization. Treg cells with a skin-homing phenotype in skin dLNs expressed high levels of IL-10, suggesting that they contribute to renewal and maintenance of the cutaneous IL-10⁺ Treg cell population.

CONCLUSION

Skin-resident Treg cells limit percutaneous sensitization by suppressing antigen-bearing DC migration through in situ IL-10 production.

T Follicular Helper Cell Biology: A Decade of Discovery and Diseases

Helping B cells and antibody responses is a major function of CD4+ T cells. It has been 10 years since the publication of Bcl6 as the lineage-defining transcription factor for T follicular helper (Tfh) differentiation and the requirement of Tfh cells as the specialized subset of CD4+ T cells needed for germinal centers (the microanatomical sites of B cell mutation and antibody affinity maturation) and related B cell responses. A great deal has been learned about Tfh cells in the past 10 years, particularly regarding their roles in a surprising range of diseases. Advances in the understanding of Tfh cell differentiation and function are discussed, as are the understanding of Tfh cells in infectious diseases, vaccines, autoimmune diseases, allergies, atherosclerosis, organ transplants, and cancer. This includes discussion of Tfh cells in the human immune system. Based on the discoveries to date, the next decade of Tfh research surely holds many more surprises. VIDEO ABSTRACT.

HSV-1 single-cell analysis reveals the activation of anti-viral and developmental programs in distinct sub-populations

Viral infection is usually studied at the population level by averaging over millions of cells. However, infection at the single-cell level is highly heterogeneous, with most infected cells giving rise to no or few viral progeny while some cells produce thousands. Analysis of Herpes Simplex virus 1 (HSV-1) infection by population-averaged measurements has taught us a lot about the course of viral infection, but has also produced contradictory results, such as the concurrent activation and inhibition of type I interferon signaling during infection. Here, we combine live-cell imaging and single-cell RNA sequencing to characterize viral and host transcriptional heterogeneity during HSV-1 infection of primary human cells. We find extreme variability in the level of viral gene expression among individually infected cells and show that these cells cluster into transcriptionally distinct sub-populations. We find that anti-viral signaling is initiated in a rare group of abortively infected cells, while highly infected cells undergo cellular reprogramming to an embryonic-like transcriptional state. This reprogramming involves the recruitment of β-catenin to the host nucleus and viral replication compartments, and is required for late viral gene expression and progeny production. These findings uncover the transcriptional differences in cells with variable infection outcomes and shed new light on the manipulation of host pathways by HSV-1.

Immune Exhaustion: Past Lessons and New Insights from Lymphocytic Choriomeningitis Virus

Lymphocytic choriomeningitis virus (LCMV) is a paradigm-forming experimental system with a remarkable track record of contributing to the discovery of many of the fundamental concepts of modern immunology. The ability of LCMV to establish a chronic infection in immunocompetent adult mice was instrumental for identifying T cell exhaustion and this system has been invaluable for uncovering the complexity, regulators, and consequences of this state. These findings have been directly relevant for understanding why ineffective T cell responses commonly arise during many chronic infections including HIV and HCV, as well as during tumor outgrowth. The principal feature of exhausted T cells is the inability to elaborate the array of effector functions necessary to contain the underlying infection or tumor. Using LCMV to determine how to prevent and reverse T cell exhaustion has highlighted the potential of checkpoint blockade therapies, most notably PD-1 inhibition strategies, for improving cellular immunity under conditions of antigen persistence. Here, we discuss the discovery, properties, and regulators of exhausted T cells and highlight how LCMV has been at the forefront of advancing our understanding of these ineffective responses.

A ten-acious cytokine for a tenacious infection

T follicular helper cells produce interleukin-10 during chronic viral infections to support the humoral response.