Search

BackgroundTreg cells have been shown to be an important part of immune-homeostasis and IL-2 which is produced upon T cell receptor (TCR)-dependent activation of T lymphocytes has been demonstrated to critically participate in Treg development.ObjectiveTo evaluate small molecule inhibitors (SMI) for the identification of novel IL-2/Treg enhancing compounds.Materials and methodsWe used TCR-dependent and allergen-specific cytokine secretion of human and mouse T cells, next generation messenger ribonucleic acid sequencing (RNA-Seq) and two different models of allergic airway inflammation to examine lead SMI-compounds.ResultsWe show here that the reported 3-phosphoinositide dependent kinase-1 (PDK1) SMI BX-795 increased IL-2 in culture supernatants of Jurkat E6-1 T cells, human peripheral blood mononuclear cells (hPBMC) and allergen-specific mouse T cells upon TCR-dependent and allergen-specific stimulation while concomitantly inhibiting Th2 cytokine secretion. RNA-Seq revealed that the presence of BX-795 during allergen-specific activation of T cells induces a bona fide Treg cell type highly similar to iTreg but lacking Foxp3 expression. When applied in mugwort pollen and house dust mite extract-based models of airway inflammation, BX-795 significantly inhibited Th2 inflammation including expression of Th2 signature transcription factors and cytokines and influx into the lungs of type 2-associated inflammatory cells such as eosinophils.ConclusionsBX-795 potently uncouples IL-2 production from Th2 inflammation and induces Th-IL-2 cells, which highly resemble induced (i)Tregs. Thus, BX-795 may be a useful new compound for the treatment of allergic diseases.

Roquin proteins preclude spontaneous T cell activation and aberrant differentiation of T follicular helper (Tfh) or T helper 17 (Th17) cells. Here we showed that deletion of Roquin-encoding alleles specifically in regulatory T (Treg) cells also caused the activation of conventional T cells. Roquin-deficient Treg cells downregulated CD25, acquired a follicular Treg (Tfr) cell phenotype, and suppressed germinal center reactions but could not protect from colitis. Roquin inhibited the PI3K-mTOR signaling pathway by upregulation of Pten through interfering with miR-17 similar to 92 binding to an overlapping cis-element in the Pten 3' UTR, and downregulated the Foxo1-specific E3 ubiquitin ligase Itch. Loss of Roquin enhanced Akt-mTOR signaling and protein synthesis, whereas inhibition of PI3K or mTOR in Roquin-deficient T cells corrected enhanced Tfh and Th17 or reduced iTreg cell differentiation. Thereby, Roquin-mediated control of PI3K-mTOR signaling prevents autoimmunity by restraining activation and differentiation of conventional T cells and specialization of Treg cells.

Anabolic metabolism of antigen-stimulated T cells is coordinated by mTOR which is activated by TCR and IL-2 signals. We show that mTORC1 regulates both the exit of quiescence and later divisions as Raptor-deficient T cells proceed 3x slower through each cell division in vivo. We noticed that following stimulation the amount of RNA per cell increases dramatically (10–40x) and is reduced to ~50% in Raptor-, but not Rictor-deficient T cells. RNAseq data indicate that this applies to all RNA polymerase I- and II-dependent biotypes. Using Coulter volume measurements, RNA-, FISH- and imaging-flow cytometry we determined that following stimulation the cell volume increases five-fold. It consists of the increase of nuclear volume and nucleolar rRNA synthesis on day 1 and a further increase of cytoplasmic volume on day 2. Raptor-deficiency delays and diminishes the growth of these cellular compartments, decreases ribosomal biosynthesis and thus the cell volume. Inhibitors of rRNA transcription block cell cycle progression at two checkpoints, of which only the G1/S transition is regulated by Raptor. We found that mTORC1 activity depends on ongoing rRNA synthesis in early activation and regulates the further synthesis rate. Altogether our data show that mTOR-adjusted cell physiology and the biosynthesis of ribosomal ‘hardware’ are reciprocally regulated during clonal T cell expansion.

Exhausted immune responses to chronic diseases represent a major challenge to global health. To explore their cell fate and plasticity in exhaustion, we analyzed CD4+T cells in a mouse model with regulatable antigen presentation. When the cells are driven through the effector phase, and are then exposed to different levels of persistent antigen, they lose their Th1 functions, upregulate exhaustion markers, resemble naturally anergic cells and become unable to help B cells and, at the highest dose, undergo apoptosis. Mechanistically, TCR signaling pathways are modulated with increasing dose and time. Ca2+ fluxes were found to be more robust to persistent antigen presentation while the MAPK and Akt pathways are easily desensitized. Transcriptomic analyses show the dynamic adjustment of gene expression and the accumulation of TCR signals over a period of weeks. Upon antigen removal, the cells recover their functionality while losing exhaustion and anergy markers. Preliminary data indicate that antigen-exhausted CD4+T cells retain their plasticity for at least 30 days and are able to adjust to different levels of antigen. Our data suggest a dynamic response of CD4+ T cells to different levels of persisting antigen and contribute to a better understanding of chronic disease.

Exhausted immune responses to chronic diseases represent a major challenge to global health. We studied CD4+ T cells in a mouse model where presentation of their antigen can be regulated. When the cells are driven through the effector phase, but are then exposed to different levels of persistent antigen, they lose their Th1 functions, upregulate exhaustion and anergy markers, modulate their MAP kinase, mTORC1 and Ca2+/calcineurin signaling pathways with dose and time, lose their capacity to transmit help to B cells and undergo, at the highest dose, apoptosis. Transcriptomic analyses show the dynamic adjustment of gene expression and the accumulation of TCR signals over a period of weeks. The cells also adapt to antigen removal and recover their functionality while losing exhaustion and anergy markers. Our data suggest an adjustable response of CD4+ T cells to different levels of persisting antigen and contribute to a better understanding of chronic disease.

Follicular dendritic cells (FDCs) are stromal cells residing in primary follicles and in germinal centers of secondary and tertiary lymphoid organs (SLOs and TLOs). There, they play a crucial role in B-cell activation and affinity maturation of antibodies. FDCs have the unique capacity to bind and retain native antigen in B-cell follicles for long periods of time. Therefore, FDCs shape the B-cell antigenome (the sum of all B-cell antigens) in SLOs and TLOs. In this review, we discuss recent findings that explain how this stromal cell type can arise in almost any tissue during TLO formation and, furthermore, focus on the mechanisms of antigen capture and retention involved in the generation of long-lasting antigen depots displayed on FDCs. Follicular dendritic cells (FDCs) are cells of stromal origin that are indispensable for secondary lymphoid organ (SLO) and tertiary lymphoid organ (TLO) development and maintenance. They are located in the central region of primary follicles and in the light zone of germinal centers [GCs; (1, 2)]. Their most striking feature is the ability to capture and retain native antigen. This was first observed in 1965, when Mitchell and Abbott analyzed the location of iodine-125 labeled flagella of Salmonella Adelaide in draining lymph nodes of mice using high-resolution electron microscopic autoradiographs (3). Since then, the role of FDCs as crucial players in antibody responses has been widely accepted. Their main function being the presentation of native antigen, in the form of immune complexes (ICs), to B cells, thereby driving their affinity maturation during the GC reaction. In this review, we focus first on recent findings that help to explain, how FDCs can arise in almost any tissue undergoing TLO formation and, second, on their ability to retain antigen in B-cell follicles. For a more detailed description of FDC biology, we refer the reader to other recent reviews (4, 5)., Frontiers in Immunology, 7, ISSN:1664-3224

Certain autoimmune diseases as well as asthma have increased in recent decades, particularly in developed countries. The hygiene hypothesis has been the prevailing model to account for this increase; however, epidemiology studies also support the contribution of diet and obesity to inflammatory diseases. Diet affects the composition of the gut microbiota, and recent studies have identified various molecules and mechanisms that connect diet, the gut microbiota, and immune responses. Herein, we discuss the effects of microbial metabolites, such as short chain fatty acids, on epithelial integrity as well as immune cell function. We propose that dysbiosis contributes to compromised epithelial integrity and disrupted immune tolerance. In addition, dietary molecules affect the function of immune cells directly, particularly through lipid G-protein coupled receptors such as GPR43.

The gut microbiota has recently been recognized for its role in immune regulation, and changes in gut microbiota may be the basis for an increased incidence of autoimmune diseases and asthma in developed countries. Beneficial microbes produce factors that are distributed systemically, and therefore can influence peripheral inflammatory responses. Such symbiosis factors are important for the control and resolution of inflammation and autoimmune diseases. Here we discuss immune regulation by recently identified symbiosis factors and how certain environmental factors favor their production and influence the composition of the gut microflora.

Follicular dendritic cells (FDCs) were originally identified by their specific morphology and by their ability to trap immune-complexed antigen in B cell follicles. By virtue of the latter as well as the provision of chemokines, adhesion molecules, and trophic factors, FDCs participate in the shaping of B cell responses. Importantly, FDCs also supply tingible body macrophages (TBMs) with the eat-me-signaling molecule milk fat globule-EGF factor 8 (Mfge8), thereby enabling the disposal of apoptotic B cells. Recent studies have provided fundamental insights into the multiple functions of FDCs in both physiological and pathophysiological contexts and into their origin. Here we review these findings, and discuss current concepts related to FDC histogenesis both in lymphoid organs and in inflammatory lymphoneogenesis.

The secreted phosphatidylserine-binding protein milk fat globule epidermal growth factor 8 (Mfge8) mediates engulfment of apoptotic germinal center B cells by tingible-body macrophages (TBMphis). Impairment of this process can contribute to autoimmunity. We show that Mfge8 is identical to the mouse follicular dendritic cell (FDC) marker FDC-M1. In bone-marrow chimeras between wild-type and Mfge8(-/-) mice, all splenic Mfge8 was derived from FDCs rather than TBMphis. However, Mfge8(-/-) TBMphis acquired and displayed Mfge8 only when embedded in Mfge8(+/+) stroma, or when situated in lymph nodes draining exogenous recombinant Mfge8. These findings indicate a licensing role for FDCs in TBMphi-mediated removal of excess B cells. Lymphotoxin-deficient mice lacked FDCs and splenic Mfge8, and suffer from autoimmunity similar to Mfge8(-/-) mice. Hence, FDCs facilitate TBMphi-mediated corpse removal, and their malfunction may be involved in autoimmunity.

Prior to invading the nervous system, prions frequently colonize lymphoid organs and sites of inflammatory lymphoneogenesis, where they colocalize with Mfge8+ follicular dendritic cells (FDCs). Here, we report that soft-tissue granulomas, a frequent feature of chronic inflammation, expressed the cellular prion protein (PrPC, encoded by Prnp) and the lymphotoxin receptor (LTbetaR), even though they lacked FDCs and did not display lymphoneogenesis. After intraperitoneal prion inoculation, granulomas of Prnp(+/+) mice, but not Prnp(-/-) granulomas or unaffected Prnp(+/+) skin, accumulated prion infectivity and disease-associated prion protein. Bone-marrow transfers between Prnp(+/+) and Prnp(-/-) mice and administration of lymphotoxin signaling antagonists indicated that prion replication required radioresistant PrPC-expressing cells and LTbetaR signaling. Granulomatous PrPC was mainly expressed by stromal LTbetaR+ mesenchymal cells that were absent from unaffected subcutis. Hence, granulomas can act as clinically silent reservoirs of prion infectivity. Furthermore, lymphotoxin-dependent prion replication can occur in inflammatory stromal cells that are distinct from FDCs.

We have studied the role of CD21/35, which bind derivatives of complement factors C3 and C4, in extraneural prion replication and neuroinvasion. Upon administration of small prion inocula, CD21/35−/− mice experienced lower attack rates and delayed disease over both wild-type (WT) mice and mice with combined C3 and C4 deficiencies. Early after inoculation, CD21/35−/− spleens were devoid of infectivity. Reciprocal adoptive bone marrow transfers between WT and CD21/35−/− mice revealed that protection from prion infection resulted from ablation of stromal, but not hemopoietic, CD21/35. Further adoptive transfer experiments between WT mice and mice devoid of both the cellular prion protein PrPC and CD21/35 showed that splenic retention of inoculum depended on stromal CD21/35 expression. Because both PrPC and CD21/35 are highly expressed on follicular dendritic cells, CD21/35 appears to be involved in targeting prions to follicular dendritic cells and expediting neuroinvasion following peripheral exposure to prions.