Extrafollicular plasmablast present in the acute phase of infections express high levels of PD-L1 and are able to limit T cell respose

During infections with protozoan parasites or some viruses, T cell immunosuppression is generated simultaneously with a high B cell activation. It has been described that, as well as producing antibodies, plasmablasts, the differentiation product of activated B cells, can condition the development of protective immunity in infections. Here, we show that, in T. cruzi infection, all the plasmablasts detected during the acute phase of the infection had higher surface expression of PD-L1 than other mononuclear cells. PD-L1hi plasmablasts were induced in vivo in a BCR-specific manner and required help from Bcl-6+CD4+T cells. PD-L1hi expression was not a characteristic of all antibody-secreting cells since plasma cells found during the chronic phase of infection expressed PD-L1 but at lower levels. PD-L1hi plasmablasts were also present in mice infected with Plasmodium or with lymphocytic choriomeningitis virus, but not in mice with autoimmune disorders or immunized with T cell-dependent antigens. In vitro experiments showed that PD-L1hi plasmablasts suppressed the T cell response, partially via PD-L1. Thus, this study reveals that extrafollicular PD-L1hi plasmablasts, whose peaks of response precede the peak of germinal center response, may have a modulatory function in infections, thus influencing T cell response.Fil: Gorosito Serran, Melisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Fiocca Vernengo, Facundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Almada, Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Beccaria, Cristian Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Gazzoni, Yamila Natali. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Canete, Pablo F.. Australian National University; ArubaFil: Roco, Jonathan A.. Australian National University; ArubaFil: Tosello Boari, Jimena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Ramello, María Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Wehrens, Ellen. University of California; Estados UnidosFil: Cai, Yeping. Australian National University; ArubaFil: Zuniga, Elina Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Montes, Carolina Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Cockburn, Ian A.. Australian National University; ArubaFil: Acosta Rodriguez, Eva Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Vinuesa, Carola G.. Australian National University; ArubaFil: Gruppi, Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; Argentin

Human Regulatory T Cell Suppressive Function Is Independent of Apoptosis Induction in Activated Effector T Cells

CD4(+)CD25(+)FOXP3(+) Regulatory T cells (Treg) play a central role in the immune balance to prevent autoimmune disease. One outstanding question is how Tregs suppress effector immune responses in human. Experiments in mice demonstrated that Treg restrict effector T cell (Teff) responses by deprivation of the growth factor IL-2 through Treg consumption, resulting in apoptosis of Teff.In this study we investigated the relevance of Teff apoptosis induction to human Treg function. To this end, we studied naturally occurring Treg (nTreg) from peripheral blood of healthy donors, and, to investigate Treg function in inflammation in vivo, Treg from synovial fluid of Juvenile Idiopathic Arthritis (JIA) patients (SF-Treg). Both nTreg and SF-Treg suppress Teff proliferation and cytokine production efficiently as predicted. However, in contrast with murine Treg, neither nTreg nor SF-Treg induce apoptosis in Teff. Furthermore, exogenously supplied IL-2 and IL-7 reverse suppression, but do not influence apoptosis of Teff.Our functional data here support that Treg are excellent clinical targets to counteract autoimmune diseases. For optimal functional outcome in human clinical trials, future work should focus on the ability of Treg to suppress proliferation and cytokine production of Teff, rather than induction of Teff apoptosis

Self-Sustained Resistance to Suppression of CD8+ Teff Cells at the Site of Autoimmune Inflammation Can Be Reversed by Tumor Necrosis Factor and Interferon-γ Blockade

OBJECTIVE: Resistance of effector T cells (Teff) to regulatory T cell (Treg)-mediated suppression contributes to the breakdown of peripheral tolerance in the inflamed joints of Juvenile Idiopathic Arthritis (JIA) patients. However, an unanswered question is whether this resistant phenotype is self-sustained and whether CD8(+) and CD4(+) Teff share the same mechanism of resistance to suppression. Here, we investigated CD8(+) Teff intrinsic resistance to suppression and how this can be targeted therapeutically. METHODS: CD8(+) or CD4(+) Teff were cultured with or without antigen presenting cells (APC) in Treg-dependent and -independent suppression assays. Synovial fluid (SF)-derived Teff were cross-cultured with peripheral blood (PB) Treg from JIA patients or healthy controls. TNF-α or IFN-γ blocking agents were used to restore Teff responsiveness to suppression. RESULTS: Suppression of cell proliferation and cytokine production by CD8(+) Teff from the SF of JIA patients was severely impaired compared to PB of JIA patients, regardless of APC and CD4(+) Teff cell presence. Similarly to CD4(+) Teff, impaired suppression of CD8(+) Teff was shown to be an intrinsic feature of this cell population. Whereas TNF-α blockade rescued both CD8(+) and CD4(+) Teff resistance, autocrine release of IFN-γ selectively sustained CD8(+) Teff resistance, which could be relieved by IFN-γ blockade. CONCLUSION: Unlike CD4(+) Teff, resistance of CD8(+) Teff to suppression at the site of autoimmune inflammation is maintained by autocrine release of IFN-γ and blockade of IFN-γ restores CD8(+) Teff responsiveness to suppression. These findings indicate a potential therapeutic value of blocking IFN-γ to restore immune regulation in JIA. This article is protected by copyright. All rights reserved

Interleukin-27R Signaling Mediates Early Viral Containment and Impacts Innate and Adaptive Immunity after Chronic Lymphocytic Choriomeningitis Virus Infection.

Chronic viral infections represent a major challenge to the host immune response, and a unique network of immunological elements, including cytokines, are required for their containment. By using a model persistent infection with the natural murine pathogen lymphocytic choriomeningitis virus clone 13 (LCMV Cl13) we investigated the role of one such cytokine, interleukin-27 (IL-27), in the control of chronic infection. We found that IL-27 receptor (IL-27R) signaling promoted control of LCMV Cl13 as early as days 1 and 5 after infection and that il27p28 transcripts were rapidly elevated in multiple subsets of dendritic cells (DCs) and myeloid cells. In particular, plasmacytoid DCs (pDCs), the most potent type 1 interferon (IFN-I)-producing cells, significantly increased il27p28 in a Toll-like receptor 7 (TLR7)-dependent fashion. Notably, mice deficient in an IL-27-specific receptor, WSX-1, exhibited a pleiotropy of innate and adaptive immune alterations after chronic lymphocytic choriomeningitis virus (LCMV) infection, including compromised NK cell cytotoxicity and antibody responses. While, the majority of these immune alterations appeared to be cell extrinsic, cell-intrinsic IL-27R was necessary to maintain early pDC numbers, which, alongside lower IFN-I transcription in CD11b+ DCs and myeloid cells, may explain the compromised IFN-I elevation that we observed early after LCMV Cl13 infection in IL-27R-deficient mice. Together, these data highlight the critical role of IL-27 in enabling optimal antiviral immunity early and late after infection with a systemic persistent virus and suggest that a previously unrecognized positive-feedback loop mediated by IL-27 in pDCs might be involved in this process.IMPORTANCE Persistently replicating pathogens, such as human immunodeficiency virus, hepatitis B virus, and hepatitis C virus, represent major health problems worldwide. These infections impose a long-term challenge on the host immune system, which must be heavily and continuously regulated to keep pathogen replication in check without causing fatal immunopathology. Using a persistently replicating rodent pathogen, LCMV, in its natural host, we identified the cellular sources and effects of one important regulatory pathway, interleukin-27 receptor WSX-1 signaling, that is required for both very early and late restriction of chronic (but not acute) infection. We found that WSX-1 was necessary to promote innate immunity and the development of aberrant adaptive immune responses. This not only highlights the role of IL-27 receptor signaling in regulating distinct host responses that are known to be necessary to control chronic infections, but also positions IL-27 as a potential therapeutic target for their modulation

IL-27 regulates the number, function and cytotoxic program of antiviral CD4 T cells and promotes cytomegalovirus persistence

<div><p>The role of IL-27 in antiviral immunity is still incompletely understood, especially in the context of chronic viruses that induce a unique environment in their infected host. Cytomegalovirus (CMV) establishes a persistent, tissue localized infection followed by lifelong latency. CMV infects the majority of people and although asymptomatic in healthy individuals, can cause serious disease or death in those with naïve or compromised immune systems. Therefore, there is an urgent need to develop a protective CMV vaccine for people at-risk and identifying key regulators of the protective immune response towards CMV will be crucial. Here we studied mouse CMV (MCMV) in IL-27 receptor deficient animals (<i>Il27ra</i>^<i>-/-</i>) to assess the role of IL-27 in regulating CMV immunity. We found that IL-27 enhanced the number of antiviral CD4 T cells upon infection. However, in contrast to a well-established role for CD4 T cells in controlling persistent replication and a positive effect of IL-27 on their numbers, IL-27 promoted MCMV persistence in the salivary gland. This coincided with IL-27 mediated induction of IL-10 production in CD4 T cells. Moreover, IL-27 reduced expression of the transcription factor T-bet and restricted a cytotoxic phenotype in antiviral CD4 T cells. This is a highly intriguing result given the profound cytotoxic phenotype of CMV-specific CD4 T cells seen in humans and we established that dendritic cell derived IL-27 was responsible for this effect. Together, these data show that IL-27 regulates the number and effector functions of MCMV-specific CD4 T cells and could be targeted to enhance control of persistent/latent infection.</p></div

Self-Renewal and Toll-like Receptor Signaling Sustain Exhausted Plasmacytoid Dendritic Cells during Chronic Viral Infection

Although characterization of T&nbsp;cell exhaustion has unlocked powerful immunotherapies, the mechanisms sustaining adaptations of short-lived innate cells to chronic inflammatory settings remain unknown. During murine chronic viral infection, we found that concerted events in bone marrow and spleen mediated by type I interferon (IFN-I) and Toll-like receptor 7 (TLR7) maintained a pool of functionally exhausted plasmacytoid dendritic cells (pDCs). In the bone marrow, IFN-I compromised the number and the developmental capacity of pDC progenitors, which generated dysfunctional pDCs. Concurrently, exhausted pDCs in the periphery were maintained by self-renewal via IFN-I- and TLR7-induced proliferation of CD4- subsets. On the other hand, pDC functional loss was mediated by TLR7, leading to compromised IFN-I production and resistance to secondary infection. These findings unveil the mechanisms sustaining a self-perpetuating pool of functionally exhausted pDCs and provide a framework for deciphering long-term exhaustion of other short-lived innate cells during chronic inflammation

IL-27 restricts the development of MCMV-specific CD4 T cells displaying a cytotoxic phenotype.

<p>WT and <i>Il27ra</i>^<i>-/-</i> mice were infected with 1*10⁴ PFU MCMV and the proportion of polyclonal CD11a⁺CD49d⁺ CD4 T cells expressing KLRG1 were analyzed throughout the course of infection in the blood (A) and in the spleen at day 21 (B) and day 40 p.i. (C). (D) The proportion of KLRG1 expressing M09_133-147 specific CD4 T cells in the spleen at day 40 p.i. (E) Proportion of CD11a⁺CD49d⁺ CD4 T cells expressing granzyme A (GrzA) in the spleen at day 21 p.i. (F) The proportion of CD4 T cells that express CD107a upon PMA/ion stimulation in the spleen at day 7 p.i. (G-H) Proportion of polyclonal CD11a⁺CD49d⁺ CD4 T cells expressing NKG2D (G) and FasL (H) in the spleen at day 21 p.i. All data are representative of at least 2 independent experiments with n = 4–5 mice per group. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.</p

IL-27 induces IL-10 production by CD4 T cells upon MCMV infection.

<p>WT and <i>Il27ra</i>^<i>-/-</i> mice were infected with 1*10⁴ PFU MCMV. The proportion (A) and number (B) of IL-10 producing CD4 T cells upon PMA/ion stimulation were analyzed in the spleen at day 21 p.i. (C) The proportion and number of IFNγ producing CD4 T cells were determined upon M09_133-147, M25_409-423, M139_560-574 and M142_24-38 peptide specific restimulation in the spleen at day 40 p.i. (A-B) one representative of two independent experiments with n = 5 mice per group. (C) one representative of 3 independent experiments with n = 4–5 mice per group * p < 0.05, **** p < 0.0001.</p