Tr1 Cells Emerge and Suppress Effector Th17 Cells in Glomerulonephritis.

T regulatory type 1 (Tr1) cells, which are defined by their regulatory function, lack of Foxp3, and high expression of IL-10, CD49b, and LAG-3, are known to be able to suppress Th1 and Th17 in the intestine. Th1 and Th17 cells are also the main drivers of crescentic glomerulonephritis (GN), the most severe form of renal autoimmune disease. However, whether Tr1 cells emerge in renal inflammation and, moreover, whether they exhibit regulatory function during GN have not been thoroughly investigated yet. To address these questions, we used a mouse model of experimental crescentic GN and double Foxp3mRFP IL-10eGFP reporter mice. We found that Foxp3neg IL-10-producing CD4+ T cells infiltrate the kidneys during GN progression. Using single-cell RNA sequencing, we could show that these cells express the core transcriptional factors characteristic of Tr1 cells. In line with this, Tr1 cells showed a strong suppressive activity ex vivo and were protective in experimental crescentic GN in vivo. Finally, we could also identify Tr1 cells in the kidneys of patients with antineutrophil cytoplasmic autoantibody-associated GN and define their transcriptional profile. Tr1 cells are currently used in several immune-mediated inflammatory diseases, such as T-cell therapy. Thus, our study provides proof of concept for Tr1 cell-based therapies in experimental GN.

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.

Reduced interleukin-2 responsiveness impairs the ability of Treg cells to compete for IL-2 in nonobese diabetic mice.

Enhancement of regulatory T cell (Treg cell) frequency and function is the goal of many therapeutic strategies aimed at treating type 1 diabetes (T1D). The interleukin-2 (IL-2) pathway, which has been strongly implicated in T1D susceptibility in both humans and mice, is a master regulator of Treg cell homeostasis and function. We investigated how IL-2 pathway defects impact Treg cells in T1D-susceptible nonobese diabetic (NOD) mice in comparison with protected C57BL/6 and NOD congenic mice. NOD Treg cells were reduced in frequency specifically in the lymph nodes and expressed lower levels of CD25 and CD39/CD73 immunosuppressive molecules. In the spleen and blood, Treg cell frequency was preserved through expansion of CD25(low), effector phenotype Treg cells. Reduced CD25 expression led to decreased IL-2 signaling in NOD Treg cells. In vivo, treatment with IL-2-anti-IL-2 antibody complexes led to effective upregulation of suppressive molecules on NOD Treg cells in the spleen and blood, but had reduced efficacy on lymph node Treg cells. In contrast, NOD CD8(+) and CD4(+) effector T cells were not impaired in their response to IL-2 therapy. We conclude that NOD Treg cells have an impaired responsiveness to IL-2 that reduces their ability to compete for a limited supply of IL-2.

Multicytokine-producing CD4+ T cells characterize the livers of patients with NASH.

A role of CD4+ T cells during the progression from nonalcoholic fatty liver disease (NAFLD) to nonalcoholic steatohepatitis (NASH) has been suggested, but which polarization state of these cells characterizes this progression and the development of fibrosis remain unclear. In addition, a gut-liver axis has been suggested to play a role in NASH, but the role of CD4+ T cells in this axis has just begun to be investigated. Combining single-cell RNA sequencing and multiple-parameter flow cytometry, we provide the first cell atlas to our knowledge focused on liver-infiltrating CD4+ T cells in patients with NAFLD and NASH, showing that NASH is characterized by a population of multicytokine-producing CD4+ T cells. Among these cells, only those with a Th17 polarization state were enriched in patients with advanced fibrosis. In parallel, we observed that Bacteroides appeared to be enriched in the intestine of NASH patients and to correlate with the frequency of multicytokine-producing CD4+ T cells. In short, we deliver a CD4+ T cell atlas of NAFLD and NASH, providing the rationale to target CD4+ T cells with a Th17 polarization state to block fibrosis development. Finally, our data offer an early indication to test whether multicytokine-producing CD4+ T cells are part of the gut-liver axis characterizing NASH.

Murine T-Helper Cell Differentiation and Plasticity.

CD4+ T helper (TH) cells are key mediators of immunity, and according to their effector functions, they can be divided into different subsets, namely, TH1, TH2, TH17, and TH22. In order to maintain systemic homeostasis and peripheral tolerance, CD4+ TH cells are counterbalanced by CD4+ T cells with regulatory properties, namely, Foxp3+ regulatory T cells (Foxp3+TREG) and TR1 cells. Here, we describe how to in vitro differentiate murine naïve CD4+ T cells toward helper (TH1, TH2, TH17, and TH22) and regulatory (Foxp3+TREG and TR1) cells.

Functional heterogeneity of CD4+ T cells in liver inflammation.

CD4+ T cells play an essential role in orchestrating adequate immunity, but their overactivity has been associated with the development of immune-mediated inflammatory diseases, including liver inflammatory diseases. These cells can be subclassified according to their maturation stage, cytokine profile, and pro or anti-inflammatory functions, i.e., functional heterogeneity. In this review, we summarize what has been discovered so far regarding the role of the different CD4+ T cell polarization states in the progression of two prominent and still different liver inflammatory diseases: non-alcoholic steatohepatitis (NASH) and autoimmune hepatitis (AIH). Finally, the potential of CD4+ T cells as a therapeutic target in both NASH and AIH is discussed.

Maturation trajectories and transcriptional landscape of plasmablasts and autoreactive B cells in COVID-19.

In parasite and viral infections, aberrant B cell responses can suppress germinal center reactions thereby blunting long-lived memory and may provoke immunopathology including autoimmunity. Using COVID-19 as model, we set out to identify serological, cellular, and transcriptomic imprints of pathological responses linked to autoreactive B cells at single-cell resolution. We show that excessive plasmablast expansions are prognostically adverse and correlate with autoantibody production but do not hinder the formation of neutralizing antibodies. Although plasmablasts followed interleukin-4 (IL-4) and BAFF-driven developmental trajectories, were polyclonal, and not enriched in autoreactive B cells, we identified two memory populations (CD80+/ISG15+ and CD11c+/SOX5+/T-bet+/-) with immunogenetic and transcriptional signs of autoreactivity that may be the cellular source of autoantibodies in COVID-19 and that may persist beyond recovery. Immunomodulatory interventions discouraging such adverse responses may be useful in selected patients to shift the balance from autoreactivity toward long-term memory.

Helminth Infections Suppress the Efficacy of Vaccination against Seasonal Influenza.

Helminth parasites infect more than a quarter of the human population and inflict significant changes to the immunological status of their hosts. Here, we analyze the impact of helminth infections on the efficacy of vaccinations using Litomosoides sigmodontis-infected mice. Concurrent helminth infection reduces the quantity and quality of antibody responses to vaccination against seasonal influenza. Vaccination-induced protection against challenge infections with the human pathogenic 2009 pandemic H1N1 influenza A virus is drastically impaired in helminth-infected mice. Impaired responses are also observed if vaccinations are performed after clearance of a previous helminth infection, suggesting that individuals in helminth-endemic areas may not always benefit from vaccinations, even in the absence of an acute and diagnosable helminth infection. Mechanistically, the suppression is associated with a systemic and sustained expansion of interleukin (IL)-10-producing CD4+CD49+LAG-3+ type 1 regulatory T cells and partially abrogated by in vivo blockade of the IL-10 receptor.

HVEM and CD160: Regulators of Immunopathology During Malaria Blood-Stage.

CD8+ T cells are key players during infection with the malaria parasite Plasmodium berghei ANKA (PbA). While they cannot provide protection against blood-stage parasites, they can cause immunopathology, thus leading to the severe manifestation of cerebral malaria. Hence, the tight control of CD8+ T cell function is key in order to prevent fatal outcomes. One major mechanism to control CD8+ T cell activation, proliferation and effector function is the integration of co-inhibitory and co-stimulatory signals. In this study, we show that one such pathway, the HVEM-CD160 axis, significantly impacts CD8+ T cell regulation and thereby the incidence of cerebral malaria. Here, we show that the co-stimulatory molecule HVEM is indeed required to maintain CD8+ T effector populations during infection. Additionally, by generating a CD160-/- mouse line, we observe that the HVEM ligand CD160 counterbalances stimulatory signals in highly activated and cytotoxic CD8+ T effector cells, thereby restricting immunopathology. Importantly, CD160 is also induced on cytotoxic CD8+ T cells during acute Plasmodium falciparum malaria in humans. In conclusion, CD160 is specifically expressed on highly activated CD8+ T effector cells that are harmful during the blood-stage of malaria.