Nonprofessional Antigen-presenting Cells Research Articles

Enterococcus Induces MHC-II Expression in the Colonic Epithelium to Aggravate Graft-Versus-Host Disease

Intestinal domination by Enterococcus, a genus of Gram-positive facultative bacteria, has been associated with an increased risk of GVHD mortality in allo-HCT patients and in preclinical models. However, the immunological mechanisms underlying this association remain unclear. Several preclinical studies have demonstrated that MHC-II expression by intestinal epithelial cells (IECs) is involved in allo-antigen presentation and GVHD and can be modulated by the intestinal microbiota. MHC-II genes are constitutively expressed by professional antigen-presenting cells (APCs) but can be induced in non-professional APCs by IFN-γ. Here we reported that Enterococcus could potentially aggravate GVHD through upregulation of MHC-II expression by IECs in an IFN-γ-dependent manner. Using an MHC-disparate mouse model of GVHD (C57BL/6J into BALB/cJ), we profiled the fecal microbiome of GVHD mice by 16S rRNA sequencing and the intestinal epithelium by flow cytometry on day 7 post-transplant. We found that endogenous Enterococcus relative abundance was positively correlated with MHC-II expression by colonic IECs (CD45- CD31- EpCAM+) during GVHD ( Fig. 1a; p=0.0004; 2 replicates; n=19). To determine whether this phenotype occurs in the absence of systemic inflammation, we utilized gnotobiotic mice treated with either E. faecalis, B. producta (a bacteria genus previously associated with improved GVHD outcomes)or PBS via oral gavage. Monocolonization with E. faecalis was sufficient to upregulate MHC-II expression by colonic IECs in non-transplanted (steady-state) animals compared to PBS-treated germfree controls ( Fig. 1b; p=0.0027; 3 replicates; n=8-12/group). On the contrary, monocolonization by B. producta did not induce MHC-II expression by colonic IECs compared to germfree controls ( p=0.96). We also observed that MHC-II upregulation was promoted by specific species within the genus Enterococcus, such that compared to PBS-treated germfree controls, only E. faecalis ( p=0.0007; 3 replicates; n=8-12/group) was able to induce MHC-II expression by colonic IECs, but not E. durans ( p=0.06) , E. gallinarium ( p=0.98) and E. hirae ( p=0.99). Using a Villin-Cre IFN- γ R fl/flmouse model with genetic ablation of the IFN-γ receptor specifically in epithelial cells, we investigated whether MHC-II expression induced by Enterococcus was dependent on IFN-γ signaling. We colonized Villin-Cre pos and Villin-Cre neg littermate controls with E. faecalis via oral gavage after antibiotics decontamination (ampicillin/enrofloxacin) and profiled the intestinal epithelium. We observed that Villin-Cre posmice exhibited a significantly lower MHC-II expression in the small intestine compared to Villin-Cre negmice on day 3 post- Enterococcus colonization ( p=0.012; 2 replicates; n=7/group), suggesting that IFN-γ signaling is necessary to mediate Enterococcus interaction with the intestinal epithelium. Finally, to explore a potential intervention to reduce intestinal inflammation upon Enterococcus domination, we treated GVHD mice with either butyrate-producing B. producta or E. faecalis. Colonization with B. producta reduced fecal Enterococcus burden on day 7 post-transplant ( p=0.007; 2 replicates; n=8/group) and improved survival in GVHD mice, compared to the E. faecalis-colonized group ( p=0.002; 2 replicates; n=18-19/group). We and others have previously shown that butyrate administration can alleviate GVHD through its effects on epithelial homeostasis. To determine whether butyrate could regulate allo-antigen presentation by the intestinal epithelium, we employed the human colorectal adenocarcinoma HT-29 cell culture. We pre-treated the cells with IFNγ (100U/ml) to induce MHC-II expression, then added butyrate (5mM) to the culture for 24 hours. Butyrate treatment was sufficient to suppress MHC-II expression by HT-29 cells, compared to DMSO-treated controls ( p=0.006; 3 replicates; n=6/group). Altogether, our results suggest that one mechanism by which Enterococcus can aggravate GVHD involves the upregulation of MHC-II expression by colonic IECs, and treatment with butyrate might serve as an intervention to prevent intestinal inflammation. Further identification of the upstream mediators involved will provide additional mechanistic insight into the interaction between Enterococcus and the intestinal epithelium at steady state and during GVHD.

Identification of IL-27 as a novel regulator of major histocompatibility complex class I and class II expression, antigen presentation, and processing in intestinal epithelial cells.

Antigen presentation via major histocompatibility complex (MHC) class I and class II receptors plays a fundamental role in T cell-mediated adaptive immunity. A dysregulation of this fine-tuned recognition might result in the development of autoimmune diseases such as inflammatory bowel diseases that are characterized by chronic relapsing inflammation of the intestinal tract and a damaged intestinal epithelial barrier. While MHCII receptors are usually expressed by professional antigen presenting cells (APC) only, there is increasing evidence that non-immune cells such as intestinal epithelial cells (IEC) might express MHCII upon stimulation with IFN-γ and thus act as non-professional APC. However, little is known about other factors regulating intestinal epithelial MHC expression. Here, we identify IL-27 as an inducer of different MHCI and MHCII receptor subtypes and the invariant chain (CD74/li) in IEC via the STAT1/IRF1/CIITA axis. CIITA, MHCII, and CD74 expression was significantly increased in IEC from Crohn's disease (CD) patients with active disease compared to controls or CD patients in remission. IEC phagocytosed and digested external antigens and apoptotic cells. IL-27 strongly stimulated antigen processing via the immunoproteasome in a IRF1-dependent manner. In co-culture experiments, antigen-primed IEC strongly enhanced lymphocyte proliferation and IL-2 secretion, dependent on direct cell-cell contact. IL-27 pretreatment of IEC significantly increased CD4+ T cell proliferation and reduced IL-2 levels in lymphocytes in coculture. In summary, we identified IL-27 as a novel regulator of IEC antigen processing and presentation via MHCI and MHCII receptors, underscoring the importance of IEC as non-professional APC.

Major histocompatibility complex class II in the tumor microenvironment: functions of nonprofessional antigen-presenting cells.

Major histocompatibility complexclass-II-restricted presentation by nonprofessional antigen-presenting cells in the tumor microenvironment can regulate antitumor T-cell responses. In murine models, tumor cell-specific MHC class II expression decreases in vivo tumor growth, dependent on T cells. Tumor cell-specific MHC class II expression is associated with improved survival and response to immune checkpoint inhibitors in human cancers. Antigen-presenting cancer-associated fibroblasts (apCAF) present MHC class-II-restricted antigens and activate CD4 T cells. The role of MHC class II on apCAFs depends on the cell of origin. MHC class II on tumoral lymphatic endothelial cells leads to expansion of regulatory T cells and increased in vivo tumor growth.

Abstract SY15-01: Tumor agnostic dendritic cell vaccines

Abstract Dendritic cells (DCs) are specialized myeloid cells with the ability to uptake, process, and present antigens to T lymphocytes; they also generate cytokine and chemokine gradients that regulate immune cell trafficking, activation, and function. DCs pulsed with tumor antigens have been used as a platform for therapeutic vaccination in cancer. In a broadly tested clinical application called a DC vaccine, autologous monocyte-derived DCs (moDCs) are isolated from a patient with cancer, exposed to tumor antigens ex vivo (antigen loading), and matured before reinfusion to the patient. However, in spite of significant development and testing, DC vaccines based on antigen-loaded moDCs have delivered mixed clinical results. The suboptimal performance of DC vaccines may be due to the use of moDCs - a heterogenous population of non-professional antigen-presenting cells - and the artificial nature of the procedure used to "load" selected tumor antigens on moDCs ex vivo. To address both issues, we developed a DC vaccine that uses a population of mouse or human DC progenitors (DCPs) engineered to produce immunostimulatory cytokines. While not involving antigen loading, the new DC platform outperformed antigen-loaded moDCs in mouse models of cancer. Engineered DCPs produced professional cDC1 and cCD2 in mice, reprogrammed the tumor microenvironment to a form characterized by broad IFNg signaling, and inhibited tumors, including autochthonous models, in an antigen-agnostic fashion. In one application, engineered DCPs synergized with antigen-specific CAR-T cells to eradicate gliomas in mice. Citation Format: Michele De Palma. Tumor agnostic dendritic cell vaccines. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr SY15-01.

Autoimmune epithelitis in primary Sjögren's syndrome.

Primary Sjögren's syndrome (pSS) is characterized by an autoimmune epithelitis associated with chronic inflammation of the exocrine glands. Alterations of extra-glandular functions in pSS is associated with lymphocytic infiltrates that invade the epithelial structures of affected organs. Within epithelial tissue, the expression of class II major histocompatibility complexes and costimulatory molecules by epithelial cells acting as non-professional antigen presenting cells, leads to the activation of T and B lymphocytes through multiple cellular crosstalk pathways. Although the pathogenetic mechanisms underlying pSS have not yet been elucidated, it is accepted that glandular epithelial cells are central regulators of the local autoimmune response.

Antigen presenting cells: Professionals, amateurs, and spectators in the 'long game' of lung immunity.

The lung is frequently and repeatedly exposed to invading pathogens and thus requires constant immunosurveillance. Professional antigen presenting cells (APCs), including dendritic cells, engulf invading pathogens and present their peptides via major histocompatibility complexes (MHC) I and II, to CD8 or CD4 T cells. Epithelial cells and stromal cells (including fibroblasts) provide more than structural support, they are increasingly recognised as key players in the immune response, acting as non-professional APCs through interactions with antigen experienced T cells that migrate to the lung. The importance of the contributions of non-professional and professional APCs to T cell function in vivo, is currently unclear. This review summarises the roles of professional and non-professional APCs in lung immunity, at the steady state and following viral insult, with particular emphasis on their ability to interact with and influence T cells.

CNS Pericytes Modulate Local T Cell Infiltration in EAE.

Pericytes at the blood-brain barrier (BBB) are located between the tight endothelial cell layer of the blood vessels and astrocytic endfeet. They contribute to central nervous system (CNS) homeostasis by regulating BBB development and maintenance. Loss of pericytes results in increased numbers of infiltrating immune cells in the CNS in experimental autoimmune encephalomyelitis (EAE), the mouse model for multiple sclerosis (MS). However, little is known about their competence to modulate immune cell activation or function in CNS autoimmunity. To evaluate the capacity of pericytes to directly interact with T cells in an antigen-specific fashion and potentially (re)shape their function, we depleted major histocompatibility complex (MHC) class II from pericytes in a cell type-specific fashion and performed T cell-pericyte cocultures and EAE experiments. We found that pericytes present antigen in vitro to induce T cell activation and proliferation. In an adoptive transfer EAE experiment, pericyte-specific MHC II KO resulted in locally enhanced T cell infiltration in the CNS; even though, overall disease course of mice was not affected. Thus, pericytes may serve as non-professional antigen-presenting cells affecting states of T cell activation, thereby locally shaping lesion formation in CNS inflammation but without modulating disease severity.

Cell surface MHC-I molecules in dendritic cells undergo fast recycling but do not replenish the Rab11+Arf6+ juxtanuclear compartment to support cross-presentation

Cross-presentation of internalized antigens by MHC class I molecules (MHC-I) plays a critical role in priming of cytotoxic T cells, recognizing pathogens and tumors. It is thought that peptides derived from cross-presented antigens can be loaded on MHC I in the endoplasmic reticulum as well as in endocytic or phagocytic compartments of murine dendritic cells (DCs). However, the origin of MHC I in the latter compartments is poorly understood. Recently MHC-I trafficking through a juxtanuclear Rab11+ recycling compartment has been suggested to be required for cross-presentation of phagocytosed antigens. We have critically examined the existence of MHC I recycling and the role of Arf6, described to regulate recycling in non-professional antigen presenting cells, in DCs. We confirm fully conformed MHC I accumulation in a juxtanuclear Rab11+ compartment and localize Arf6 to this compartment. DC MHC I molecules undergo fast recycling, however, both fully conformed and “open” internalized MHC I fail to enter a putative slow recycling pathway to the Rab11+Arf6+ compartment. Arf6 knockdown increases cell surface class I density and reduces degradation of internalized “open” MHC I but does not affect fast MHC-I recycling. Moreover, it compromises cross-presentation of antigen internalized via Fc receptors but not other antigens. In conclusion, we demonstrate fast recycling of MHC I in mouse DCs but find that recycling is not required for general cross-presentation. We propose that Rab11 and Rab22, previously reported to be required for cross-presentation, mediate delivery of MHC I from the juxtanuclear compartment to phagosomes/endosomes. However, the origin of the MHC I molecules in this compartment remains to be determined.

Abstract 4160: Promoting immunogenicity of synthetic long peptide vaccines based on in vivo IgG complex formation: Preclinical evaluation and clinical entry of the TET platform

Abstract Vaccines based on synthetic long peptides, targeting immunogenic region(s) of tumor associated proteins, are becoming increasingly used in oncology. Synthetic long peptides require endogenous processing by antigen presenting cells to be presented to T cells, thus reducing the risk of antigen presentation by non-professional antigen presenting cells lacking co-stimulation receptors. The formulation and delivery strategies require further development as peptides degrade rapidly in vivo. Herein we make use of a novel targeting and adjuvant strategy to deliver peptides to antigen presenting cells. Tumor-derived peptides are coupled to a B cell epitope element (the MTTE sequence, a tetanus toxin-derived universal B cell epitope) which induce the formation of peptide-conjugate -complex formation in vivo. This strategy, further named the TET technology, makes use of pre-existing antibodies to improve the bioavailability, stability, and immunogenicity of tumor-derived peptide therapeutics. The TET technology is here used in TENDU, a first-in-class prostate cancer vaccine candidate. TENDU incorporates selected immunogenic prostate cancer epitopes derived from PAP and PSMA. The peptides are designed to include proteasome processing elements along with a unique TAP translocation element. To assess the design, a conjugate with a known DR4 epitope embedded in a longer peptide was evaluated for T cell priming in HLA-DR4 animals and displayed T cell expansion in response to a prime/boost vaccination. To ensure that prostate cancer patients respond with antibodies to the MTTE sequence after a tetanus toxoid (TTd) vaccination, both healthy controls and patients (age and gender matched) were vaccinated using a TTd-based vaccine regime. Anti-MTTE antibody titers were evaluated. Patients and HCs responded with increased IgG1 type antibodies against MTTE after TTd vaccination. Safety with regards to hypersensitivity in response to the vaccine platform was evaluated in rabbits and a human whole blood loop system without any identified adverse events. Based on preclinical data the no-observed-adverse-effect level (NOAEL) was set to 1440µg/dose. The vaccine is currently assessed in a First-in-Human clinical study (TENDU-101, 3+3 study design) in patients with relapse after a primary radical prostatectomy. No safety concerns were noted at the lowest dose level and the 400 µg dose cohort has been initiated with the first patient dosed with no reported adverse events. The study’s primary endpoints are safety and tolerability. Secondary endpoints involve cellular immune responses, systemic PSA and PAP levels along with dose level selection. In conclusion, TENDU, a first-in-class vaccine candidate is under clinical development evaluating safety and tolerability for the TET vaccine platform technology. Citation Format: Erika Fletcher, Iliana Kerzeli, Robert Cordfunke, Aikaterini Nasi, Gunilla Törnqvist, Robert Valentijn, Frida Lindqvist, Inken Dillmann, Martin Lord, Neanke Bouwman, Jacques Neefjes, Natasja Dolezal, Kees Franken, Stephanie McArdle, Murrium Ahmad, Silvia Johansson, Ferry Ossendorp, Michael Haggman, Wolfgang Lilleby, Gustav Ullenhag, Sam Ladjevardi, Justyna Jarblad, Jan Wouter Drijfhout, Sara Mangsbo. Promoting immunogenicity of synthetic long peptide vaccines based on in vivo IgG complex formation: Preclinical evaluation and clinical entry of the TET platform [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4160.

Characterization of a Novel Anti-inflammatory Biogenic Amine

Abstract Tryptophan (Trp) is an essential amino acid whose catabolism generates a cascade of over fifty molecules in a cell-specific manner. Three major Trp metabolic pathways have been described: synthesis of serotonin, synthesis of melatonin and generation of kynurenines. In mammalian cells, 90% of Trp is processed through the kynurenine pathway and kynurenine metabolites are regarded as one of the most powerful mechanism for immune regulation. We recently reported a novel biogenic amine, 3HKA, generated through a still uncharacterized lateral pathway of Trp catabolism. This novel biogenic amine is generated by both professional (Dendritic Cells) and non-professional (Lymphatic Endothelial Cells) antigen presenting cells and, differently from all others Trp metabolites, display unique “in vivo” immunosuppressive capabilities. In vitro, 3-HKA exhibited an anti-inflammatory profile by inhibiting the IFN-g-mediated STAT1/NF-kB pathway in both mouse and human dendritic cells (DCs) with a consequent decrease in the release of pro-inflammatory chemokines and cytokines; most notably, TNFa, IL-6, and IL12p70. In vivo, 3-HKA exerted protective effects in an experimental mouse model of Psoriasis by decreasing skin thickness, erythema, scaling and fissuring, reducing TNFa, IL-1b, IFN-g, and IL-17 production, and inhibiting generation of effector CD8+ T cells. Similarly, in a mouse model of nephrotoxic nephritis, besides reducing inflammatory cytokines, 3-HKA improved proteinuria and serum urea nitrogen, overall ameliorating the immune-mediated glomerulonephritis and renal dysfunction. Overall we propose that this novel biological amine is a crucial component of Trp-mediated immune tolerance.

Antigen Cross-Presentation by Murine Proximal Tubular Epithelial Cells Induces Cytotoxic and Inflammatory CD8+ T Cells.

Immune-mediated glomerular diseases are characterized by infiltration of T cells, which accumulate in the periglomerular space and tubulointerstitium in close contact to proximal and distal tubuli. Recent studies described proximal tubular epithelial cells (PTECs) as renal non-professional antigen-presenting cells that stimulate CD4+ T-cell activation. Whether PTECs have the potential to induce activation of CD8+ T cells is less clear. In this study, we aimed to investigate the capacity of PTECs for antigen cross-presentation thereby modulating CD8+ T-cell responses. We showed that PTECs expressed proteins associated with cross-presentation, internalized soluble antigen via mannose receptor-mediated endocytosis, and generated antigenic peptides by proteasomal degradation. PTECs induced an antigen-dependent CD8+ T-cell activation in the presence of soluble antigen in vitro. PTEC-activated CD8+ T cells expressed granzyme B, and exerted a cytotoxic function by killing target cells. In murine lupus nephritis, CD8+ T cells localized in close contact to proximal tubuli. We determined enhanced apoptosis in tubular cells and particularly PTECs up-regulated expression of cleaved caspase-3. Interestingly, induction of apoptosis in the inflamed kidney was reduced in the absence of CD8+ T cells. Thus, PTECs have the capacity for antigen cross-presentation thereby inducing cytotoxic CD8+ T cells in vitro, which may contribute to the pathology of immune-mediated glomerulonephritis.

Physiopathologie du Sjögren primitif : une épithélite auto-immune

Primary Gougerot–Sjögren syndrome (SSp) is characterized by an autoimmune epithelitis associated with chronic inflammation of the exocrine glands. Alterations of and extraglandular functions of SSp is associated with lymphocytic infiltrates that invade the epithelial structures of affected organs. Within epithelial tissue, the expression of major class II histocompatibility complexes (MHC II) and costimulatory molecules by epithelial cells acting as non-professional antigen presenting cells, lead to the activation of T and B lymphocytes through multiple cellular crosstalks. Although the pathogenetic pathways underlying SSp have not yet been elucidated, it is established that glandular epithelial cells are central regulators of the local autoimmune response.

Enhanced antigen cross-presentation in human colorectal cancer-associated fibroblasts through upregulation of the lysosomal protease cathepsin S

BackgroundCross-presentation of exogenous antigens in HLA-class I molecules by professional antigen presenting cells (APCs) is crucial for CD8+ T cell function. Recent murine studies show that several non-professional APCs, including...

Inhalant Mammal-Derived Lipocalin Allergens and the Innate Immunity.

A major part of important mammalian respiratory allergens belongs to the lipocalin family of proteins. By this time, 19 respiratory mammalian lipocalin allergens have been registered in the WHO/IUIS Allergen Nomenclature Database. Originally, lipocalins, small extracellular proteins (molecular mass ca. 20 kDa), were characterized as transport proteins but they are currently known to exert a variety of biological functions. The three-dimensional structure of lipocalins is well-preserved, and lipocalin allergens can exhibit high amino acid identities, in several cases more than 50%. Lipocalins contain an internal ligand-binding site where they can harbor small principally hydrophobic molecules. Another characteristic feature is their capacity to bind to specific cell-surface receptors. In all, the physicochemical properties of lipocalin allergens do not offer any straightforward explanations for their allergenicity. Allergic sensitization begins at epithelial barriers where diverse insults through pattern recognition receptors awaken innate immunity. This front-line response is manifested by epithelial barrier-associated cytokines which together with other components of immunity can initiate the sensitization process. In the following, the crucial factor in allergic sensitization is interleukin (IL)-4 which is needed for stabilizing and promoting the type 2 immune response. The source for IL-4 has been searched widely. Candidates for it may be non-professional antigen-presenting cells, such as basophils or mast cells, as well as CD4+ T cells. The synthesis of IL-4 by CD4+ T cells requires T cell receptor engagement, i.e., the recognition of allergen peptides, which also provides the specificity for sensitization. Lipocalin and innate immunity-associated cell-surface receptors are implicated in facilitating the access of lipocalin allergens into the immune system. However, the significance of this for allergic sensitization is unclear, as the recognition by these receptors has been found to produce conflicting results. As to potential adjuvants associated with mammalian lipocalin allergens, the hydrophobic ligands transported by lipocalins have not been reported to enhance sensitization while it is justified to suppose that lipopolysaccharide plays a role in it. Taken together, type 2 immunity to lipocalin allergens appears to be a harmful immune response resulting from a combination of signals involving both the innate and adaptive immunities.

The ABCs of Antigen Presentation by Stromal Non-Professional Antigen-Presenting Cells.

Professional antigen-presenting cells (APCs), such as dendritic cells and macrophages, are known for their ability to present exogenous antigens to T cells. However, many other cell types, including endothelial cells, fibroblasts, and lymph node stromal cells, are also capable of presenting exogenous antigens to either CD8+ or CD4+ T cells via cross-presentation or major histocompatibility complex (MHC) class II-mediated presentation, respectively. Antigen presentation by these stromal nonprofessional APCs differentially affect T cell function, depending on the type of cells that present the antigen, as well as the local (inflammatory) micro-environment. It has been recently appreciated that nonprofessional APCs can, as such, orchestrate immunity against pathogens, tumor survival, or rejection, and aid in the progression of various auto-immune pathologies. Therefore, the interest for these nonprofessional APCs is growing as they might be an important target for enhancing various immunotherapies. In this review, the different nonprofessional APCs are discussed, as well as their functional consequences on the T cell response, with a focus on immuno-oncology.

Autoimmune Epithelitis and Chronic Inflammation in Sjögren's Syndrome-Related Dry Eye Disease.

Autoimmune epithelitis and chronic inflammation are one of the characteristic features of the immune pathogenesis of Sjögren’s syndrome (SS)-related dry eye disease. Autoimmune epithelitis can cause the dysfunction of the excretion of tear fluid and mucin from the lacrimal glands and conjunctival epithelia and meibum from the meibomian glands. The lacrimal gland and conjunctival epithelia express major histocompatibility complex class II or human leukocyte antigen-DR and costimulatory molecules, acting as nonprofessional antigen-presenting cells for T cell and B cell activation in SS. Ocular surface epithelium dysfunction can lead to dry eye disease in SS. Considering the mechanisms underlying SS-related dry eye disease, this review highlights autoimmune epithelitis of the ocular surface, chronic inflammation, and several other molecules in the tear film, cornea, conjunctiva, lacrimal glands, and meibomian glands that represent potential targets in the treatment of SS-related dry eye disease.

Immunomodulation of endothelial cells induced by macrolide therapy in a model of septic stimulation.

ObjectivesSepsis is defined as the host's inflammatory response to a life‐threatening infection. The endothelium is implicated in immunoregulation during sepsis. Macrolides have been proposed to display immunomodulatory properties. The goal of this study was to analyze whether macrolides can exert immunomodulation of endothelial cells (ECs) in an experimental model of sepsis.MethodsHuman ECs were stimulated by proinflammatory cytokines and lipopolysaccharide before exposure to macrolides. ECs phenotypes were analyzed by flow cytometry. Cocultures of ECs and peripheral blood mononuclear cells (PBMCs) were performed to study the ECs ability to alter T‐cell viability and differentiation in the presence of macrolides. Soluble factor production was assessed.ResultsECs act as non‐professional antigen presenting cells and expressed human leukocyte antigen (HLA) antigens, the adhesion molecules CD54, CD106, and the coinhibitory molecule CD274 after septic stimulation. Incubation with macrolides induced a significant decrease of HLA class I and HLA class II HLA‐DR on septic‐stimulated ECs, but did not alter either CD54, CD106, nor CD274 expression. Interleukin‐6 (IL‐6) and IL‐8 production by stimulated ECs were unaltered by incubation with macrolides, whereas Clarithromycin exposure significantly decreased IL‐6 gene expression. In cocultures of septic ECs with PBMCs, neither the proportion of CD4 + , CD8 + T nor their viability was altered by macrolides. T‐helper lymphocyte subsets Th1, Th17, and Treg polarization by stimulated ECs were unaltered by macrolides.ConclusionThis study reports phenotypic and gene expression changes in septic‐stimulated ECs exposed to macrolides, without resulting in altered immunogenicity of ECs in co‐cultures with PBMCs. In vivo studies may help to further understand the impact of macrolide therapy on ECs immune homeostasis during sepsis.

Targeting Antigen-Presenting Cells in Multiple Sclerosis Treatment

Multiple sclerosis (MS) is common neurological disease of the central nervous system (CNS) affecting mostly young adults. Despite decades of studies, its etiology and pathogenesis are not fully unraveled and treatment is still insufficient. The vast majority of studies suggest that the immune system plays a major role in MS development. This is also supported by the effectiveness of currently available MS treatments that target immunocompetent cells. In this review, the role of antigen-presenting cells (APC) in MS development as well as the novel therapeutic options targeting those cells in MS are presented. It is known that in MS, peripheral self-antigen-specific immune cells are activated during antigen presentation process and they enter the CNS through the disrupted blood–brain barrier (BBB). Myelin-reactive CD4+ T-cells can be activated by dendritic cells, infiltrating macrophages, microglia cells, or B-cells, which all express MHC class II molecules. There are also suggestions that brain endothelial cells may act as non-professional APCs and present myelin-specific antigens with MHC class II. Similarly, astrocytes, the major glial cells in the CNS, were shown to act as non-professional APCs presenting myelin antigens to autoreactive T-cells. Several currently available MS drugs such as natalizumab, fingolimod, alemtuzumab, and ocrelizumab may modulate antigen presentation in MS. Another way to use this mechanism in MS treatment may be the usage of specific tolerogenic dendritic cells or the induction of tolerance to myelin antigens by peptide vaccines.

3-hydroxy-L-kynurenamine is an immunomodulatory biogenic amine

Tryptophan catabolism is a major metabolic pathway utilized by several professional and non-professional antigen presenting cells to maintain immunological tolerance. Here we report that 3-hydroxy-l-kynurenamine (3-HKA) is a biogenic amine produced via an alternative pathway of tryptophan metabolism. In vitro, 3-HKA has an anti-inflammatory profile by inhibiting the IFN-γ mediated STAT1/NF-κΒ pathway in both mouse and human dendritic cells (DCs) with a consequent decrease in the release of pro-inflammatory chemokines and cytokines, most notably TNF, IL-6, and IL12p70. 3-HKA has protective effects in an experimental mouse model of psoriasis by decreasing skin thickness, erythema, scaling and fissuring, reducing TNF, IL-1β, IFN-γ, and IL-17 production, and inhibiting generation of effector CD8+ T cells. Similarly, in a mouse model of nephrotoxic nephritis, besides reducing inflammatory cytokines, 3-HKA improves proteinuria and serum urea nitrogen, overall ameliorating immune-mediated glomerulonephritis and renal dysfunction. Overall, we propose that this biogenic amine is a crucial component of tryptophan-mediated immune tolerance.

The Role of Trogocytosis in the Modulation of Immune Cell Functions.

Trogocytosis is an active process, in which one cell extracts the cell fragment from another cell, leading to the transfer of cell surface molecules, together with membrane fragments. Recent reports have revealed that trogocytosis can modulate various biological responses, including adaptive and innate immune responses and homeostatic responses. Trogocytosis is evolutionally conserved from protozoan parasites to eukaryotic cells. In some cases, trogocytosis results in cell death, which is utilized as a mechanism for antibody-dependent cytotoxicity (ADCC). In other cases, trogocytosis-mediated intercellular protein transfer leads to both the acquisition of novel functions in recipient cells and the loss of cellular functions in donor cells. Trogocytosis in immune cells is typically mediated by receptor–ligand interactions, including TCR–MHC interactions and Fcγ receptor-antibody-bound molecule interactions. Additionally, trogocytosis mediates the transfer of MHC molecules to various immune and non-immune cells, which confers antigen-presenting activity on non-professional antigen-presenting cells. In this review, we summarize the recent advances in our understanding of the role of trogocytosis in immune modulation.