CD155 is essential for skeletal muscle regeneration by regulating satellite cell proliferation and differentiation.

CD155, a member of the immunoglobulin superfamily, is closely related to cell proliferation, adhesion, and migration. CD155 is overexpressed on the surface of cancer cells to promote cell proliferation and is upregulated in damaged tissues as a stress-induced molecule. The process of skeletal muscle regeneration after injury is complex and involves injurious stimulation and subsequent satellite cell proliferation. However, the role of CD155 in this process remains unelucidated. This study aimed to explore the role of CD155 in injured skeletal muscle regeneration and to clarify its effect on satellite cell proliferation and differentiation. Here, quantitative real-time polymerase chain reaction (RT-qPCR) and immunofluorescence results indicated that CD155 expression in satellite cells increased after skeletal muscle injury. CD155 knockout in mice impaired the regeneration of skeletal muscle. A bone marrow transplantation mouse model was constructed and revealed that CD155 on skeletal muscle tissues, not immune cells, affected muscle regeneration. In vitro, CD155 knockdown in myoblasts inhibited their proliferation and differentiation. The transcriptomic analysis also indicated that CD155 absence can impair the biological proliferation and differentiation process of myoblasts. Our research demonstrates that CD155 directly promotes injured muscle regeneration by regulating satellite cell proliferation and differentiation, which may be a potential therapeutic molecule for skeletal muscle injury.

Alterations in CX3CL1 Levels and Its Role in Viral Pathogenesis.

CX3CL1, also named fractalkine or neurotactin, is the only known member of the CX3C chemokine family that can chemoattract several immune cells. CX3CL1 exists in both membrane-anchored and soluble forms, with each mediating distinct biological activities. CX3CL1 signals are transmitted through its unique receptor, CX3CR1, primarily expressed in the microglia of the central nervous system (CNS). In the CNS, CX3CL1 acts as a regulator of microglia activation in response to brain disorders or inflammation. Recently, there has been a growing interest in the role of CX3CL1 in regulating cell adhesion, chemotaxis, and host immune response in viral infection. Here, we provide a comprehensive review of the changes and function of CX3CL1 in various viral infections, such as human immunodeficiency virus (HIV), SARS-CoV-2, influenza virus, and cytomegalovirus (CMV) infection, to highlight the emerging roles of CX3CL1 in viral infection and associated diseases.

CD226 knockout reduces the development of CD8+ T by impairing the TCR sensitivity of double-positive thymocytes.

The costimulation molecule CD226 is widely involved in T cell differentiation, activation and immune functional regulation in peripheral immune tissues. CD226-deficient mice have impaired immune response capacity. The function of CD226 in regulating T cell development in the thymus, a central immune organ, is not yet fully understood. We investigated the development of thymocytes using CD226 knockout mice and single-cell sequencing techniques. CD226 began to be expressed in the second half of thymocyte development, with a gradual increase from the double-positive (DP) to single-positive (SP) phase and higher levels of CD226 on CD8+ T cells than on CD4+ T cells from the SP phase to mature T cells. In the thymus of CD226KO mice, the proportion of DPT at the quiescent phase (DPT-Q) increased, of which the Gzma+ cluster that tends to be CD8+ T cells and CD5+ cluster that is undergoing positive selection decreased dramatically. Afterward, the proportion of mature CD8+ T cells reduced dramatically. Depletion of CD226 impaired TCR activation signalling and diminished AKT/ERK/NF-κB/p38 phosphorylation levels. The diminished TCR responsiveness of DPT cells impeded their positive selection process and influenced the maturation of CD8+ T cells. In mechanism, CD226 knockout enhanced DPT cell apoptosis via impairing AKT phosphorylation. These results suggest that CD226 plays a significant role in T cell thymic development via modulation of TCR signalling, affecting CD8+ T cell maturation.

CD226 deficiency exacerbated intestinal immune dysregulation in mice with dinitrochlorobenzene-induced atopic dermatitis.

Intestinal mucosal immunity plays a pivotal role in host defence. In this study, we found that cluster of differentiation 226 (CD226) gene knockout (KO) led to more severe atopic dermatitis (AD)-related skin pathologies and bowel abnormalities in a 2,4-dinitrochlorobenzene (DNCB)-induced AD-like mouse model. Following DNCB administration, the expression of CD226 was elevated in intestinal mucosal tissues, including group 3 innate lymphoid cells (ILC3s) and CD4+ T cells of Peyer's patches (PPs). CD226 deficiency led to an overactive intestinal immune response in the AD-like mice, as evidenced by increased inflammation and Th1/Th2-related cytokine levels as well as increased Paneth cell numbers and antimicrobial peptide (AMP) expression, which was likely due to the higher interleukin (IL)-22 production in the lamina propria. Additionally, CD226 deficiency increased the production of IL-4 and IL-17 in mesenteric lymph nodes as well as the number of PPs and expression of immunoglobulin (Ig) A in B cells. Moreover, insufficient expression of CD226 affected the characterization of intraepithelial and lamina propria lymphocytes in the intestinal mucosa. Finally, the number of PPs was increased in CD4+ T cell-specific CD226 KO and regulatory T (Treg) cell-specific CD226 KO mice; thus, loss of CD226 in Treg cells resulted in impaired Treg cell-suppressive function. Therefore, our findings indicate that CD226 deficiency alters intestinal immune functionality in inflammatory diseases.

Competitive binding of CD226/TIGIT with poliovirus receptor regulates macrophage polarization and is involved in vascularized skin graft rejection.

End-stage organ failure often requires solid organ transplantation. Nevertheless, transplant rejection remains an unresolved issue. The induction of donor-specific tolerance is the ultimate goal in transplantation research. In this study, an allograft vascularized skin rejection model using BALB/c-C57/BL6 mice was established to evaluate the regulation of the poliovirus receptor signaling pathway using CD226 knockout or T cell immunoglobulin and ITIM domain (TIGIT)-crystallizable fragment (Fc) recombinant protein treatment. In the TIGIT-Fc-treated and CD226 knockout groups, graft survival time prolonged significantly, with a regulatory T cell proportion increase and M2-type macrophage polarization. Donor-reactive recipient T cells became hyporesponsive while responding normally after a third-party antigen challenge. In both groups, serum interleukin (IL)-1ß, IL-6, IL-12p70, IL-17A, tumor necrosis factor-α, interferon gamma, and monocyte chemoattractant protein-1 levels decreased, and the IL-10 level increased. In vitro, M2 markers, such as Arg1 and IL-10, were markedly increased by TIGIT-Fc, whereas iNOS, IL-1ß, IL-6, IL-12p70, tumor necrosis factor-α, and interferon gamma levels decreased. CD226-Fc exerted the opposite effect. TIGIT suppressed TH1 and TH17 differentiation by inhibiting macrophage SHP-1 phosphorylation and enhanced ERK1/2-MSK1 phosphorylation and nuclear translocation of CREB. In conclusion, CD226 and TIGIT competitively bind to poliovirus receptor with activating and inhibitory functions, respectively. Mechanistically, TIGIT promotes IL-10 transcription from macrophages by activating the ERK1/2-MSK1-CREB pathway and enhancing M2-type polarization. CD226/TIGIT-poliovirus receptor are crucial regulatory molecules of allograft rejection.

HTNV infection induces activation and deficiency of CD8+MAIT cells in HFRS patients.

Hantaan virus (HTNV) infection causes an epidemic of hemorrhagic fever with renal syndrome (HFRS) mainly in Asia. Mucosal-associated invariant T (MAIT) cells are innate-like T lymphocytes known to play an important role in innate host defense during virus infection. However, their roles and phenotypes during HTNV infection have not yet been explored. We characterized CD8+MAIT cells from HFRS patients based on scRNA-seq data combined with flow cytometry data. We showed that HTNV infection caused the loss and activation of CD8+MAIT cells in the peripheral blood, which were correlated with disease severity. The production of granzyme B and IFN-γ from CD8+MAIT cells and the limitation of HTNV replication in endothelia cells indicated the anti-viral property of CD8+MAIT cells. In addition, in vitro infection of MAIT cells by HTNV or HTNV-exposed monocytes showed that the activation of MAIT cells was IL-18 mediated. In conclusion, this study identified, for the first time, gene expression profiles of MAIT cells, provided underlying molecular mechanisms for activation of MAIT cells during HTNV infection, and suggested a potential anti-viral role of MAIT cells in HFRS.

Identification of hub genes and potential inhibitory compounds in the process of liver transplantation through transcriptome sequencing.

Liver transplantation (LT) is the best choice for patients with end-stage liver diseases. In order to better understand pathophysiological alterations in LT, we aimed to identify potential hub genes and inhibitory compounds involved in the LT process. Four pairs of peripheral blood mononuclear cell (PBMC) samples of the LT recipients before and after surgery were collected and taken for transcriptome sequencing. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed for the screened differentially expressed genes (DEGs) between pre- and post-operation groups. Common DEGs were obtained from GO and KEGG enriched pathways, followed by protein-protein interaction (PPI) network construction, hub gene identification, module analysis, and structure-based virtual screening process (SBVS). Compared to the pre-operation stage, 4745 genes were down-regulated and 798 up-regulated after LT. GO analysis showed that the DEGs were enriched in ribosome-related translation regulation, and KEGG analysis indicated that infection and immune-related pathways and diseases were largely enriched. A large number of down-regulated DEGs were not only associated with ribosome-related pathways but also with the alterations of epigenetic modifications, in particular ubiquitination. Moreover, through the PPI network of 29 common genes from GO and KEGG-enriched pathways, 7 hub genes were identified, including PTEN, MYC, EIF2S1, EIF4EBP1, HSP90AB1, TP53, and HSPA8, which were mainly involved in the PI3K-AKT signaling pathway. SBVS of the seed molecule PTEN (PDB code: 1D5R) predicted top hits compounds that may serve as potential inhibitors of PTEN, of which the compound ZINC4235331 had the lowest binding affinity of -10 kcal/mol. The significance of screened hub genes and potential inhibitors involved in the process of LT provides novel therapeutic strategies for improving the outcomes of LT recipients during surgery.

Interleukin-6 absence triggers intestinal microbiota dysbiosis and mucosal immunity in mice.

Interleukin-6 (IL-6) in mucosal immune cells is involved in post-injury intestinal regeneration, inflammation responses, and gastric homeostasis. However, the interaction between IL-6 and the dynamic balance of gut microbiota (GM) remains unexplored. Intestinal pathology was assessed by hematoxylin and eosin and periodic acid-Schiff staining in wild-type (WT) and IL-6 gene knockout (KO) C57BL/6J mice. GM profiles were established via high-throughput sequencing of the fecal bacterial 16S rRNA gene. Intestinal α- and ß-defensins were measured by quantitative real-time PCR; further, flow cytometry was performed to analyze isolated intraepithelial lymphocytes (IELs). Compared with the WT, IL-6 KO did not obviously change gut structures, but significantly reduced GM diversity, resulting in reduced metabolic pathways with decreased gram-positive but elevated gram-negative bacteria. More taxa alterations included differences at the phyla (e.g., increased Verrucomicrobia and decreased Firmicutes) and genera (e.g., increased Akkermansia and decreased Lactobacillus) levels. Absence of IL-6 also significantly increased intestinal expression of defensins α3 and α4 (Defa3 and Defa4) and the percentage of natural TCRγδ+ IELs, providing a molecular basis for triggering mucosal immune response. Therefore, IL-6 loss remodels GM composition and alters IEL maintenance, identifying IL-6 as a crucial cytokine for GM dysbiosis and mucosal immunity.

CD226 deficiency promotes glutaminolysis and alleviates mitochondria damage in vascular endothelial cells under hemorrhagic shock.

Hemorrhagic shock (HS) is common in clinical emergencies, leading to millions of deaths each year globally. CD226 is a costimulatory adhesion molecule expressed on both immune cells and endothelial cells (ECs) to regulate their metabolic activity and function. As endothelial dysfunction occurs after HS, the roles CD226 plays in vascular EC metabolism were investigated. CD226fl/fl Tekcre mice were adopted to achieve vascular EC-specific knockout of CD226, and subjected to HS modelling. Serum levels of crucial intermediate metabolites were evaluated through liquid chromatography-mass spectrometry analysis. Human umbilical vein ECs (HUVECs) were used to study the effects of CD226 under hypoxia in vitro. Seahorse analysis evaluated the cellular glycolysis and mitochondria bioenergetics. Results showed that CD226 deficiency in vascular ECs alleviated HS-induced intestinal damage and inflammatory response in mice. Animal studies indicated an improved energy metabolism when CD226 was knocked out in ECs after HS, as evidenced by enhanced glutamine-glutamate metabolism and decreased lactic acid levels. Glut-1 was upregulated in mouse vascular ECs after HS and HUVECs under hypoxia, combined with decreased CD226. Moreover, HUVECs with CD226 knockdown exhibited relieved mitochondrial damage and early apoptosis under hypoxia, whereas CD226 overexpression showed opposite effects. Seahorse analysis showed that downregulated CD226 significantly increased mitochondrial ATP production and glucose uptake in HUVECs under hypoxia. Additionally, Erk/PHD2 signaling-mediated HIF-1α/Glut-1 and HIF-2α/ASCT2 pathways were involved in CD226 regulation on HUVEC glutaminolysis after hypoxia. Hence, CD226 deficiency promotes bypass energy supply to vascular ECs under ischemic or hypoxic stress, to ameliorate the stress-mediated metabolic disturbance.

CD226 Deficiency Alleviates Murine Allergic Rhinitis by Suppressing Group 2 Innate Lymphoid Cell Responses.

Allergic rhinitis (AR) is an immunoglobulin E-mediated type 2 inflammation of the nasal mucosa that is mainly driven by type 2 helper T cells (Th2) and type 2 innate lymphoid cells (ILC2s). CD226 is a costimulatory molecule associated with inflammatory response and is mainly expressed on T cells, natural killer cells, and monocytes. This study is aimed at elucidating the role of CD226 in allergic inflammatory responses in murine AR using global and CD4+ T cell-specific Cd226 knockout (KO) mice. AR nasal symptoms were assessed based on the frequency of nose rubbing and sneezing. Hematoxylin and eosin and periodic acid-Schiff staining and quantitative real-time PCR methods were used to determine eosinophils, goblet cells, and ILC2-associated mRNA levels in the nasal tissues of mice. CD226 levels on ILC2s were detected using flow cytometry, and an immunofluorescence double staining assay was employed to determine the number of ILC2s in the nasal mucosa. The results showed that global Cd226 KO mice, but not CD4+ T cell-specific Cd226 KO mice, exhibited attenuated AR nasal symptoms. Eosinophil recruitment, goblet cell proliferation, and Th2-inflammatory cytokines were significantly reduced, which resulted in the alleviation of allergic and inflammatory responses. ILC2s in the murine nasal mucosa expressed higher levels of CD226 after ovalbumin stimulation, and CD226 deficiency led to a reduction in the proportion of nasal ILC2s and ILC2-related inflammatory gene expression. Hence, the effect of CD226 on the AR mouse model may involve the regulation of ILC2 function rather than CD4+ T cells.

Adiponectin's globular domain inhibits T cell activation by interacting with LAIR-1.

Adiponectin (APN) is the most abundant adipokine in human plasma, and has insulin-sensitizing effect. Recent studies have reported that APN plays both anti- and pro-inflammatory roles under different circumstances. However, there is a lack of convincing evidence that decipher APN's anti-inflammatory role through the known receptors and their downstream signaling pathways. In this study, we evaluated a new molecular mechanism underlying APN's anti-inflammatory roles. Our results revealed that the globular domain of adiponectin (gAdp) interacted with the inhibitory leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1). In vitro experiments showed that gAdp inhibited activation of the T cells via the LAIR-1, through a process that also involved downstream SHP-2. These findings indicate that LAIR-1 is a novel APN receptor, affirming APN's anti-inflammatory effect. In summary, we have identified a novel mechanism of peripheral immunoregulatory processes that provides baseline information for further studies on gAdp's role and its contribution to inflammation.

CD226 knockout alleviates high-fat diet induced obesity by suppressing proinflammatory macrophage phenotype.

Obesity is associated with chronic low-grade inflammation, contributing to an increasing prevalence of chronic metabolic diseases, such as insulin resistance, non-alcoholic fatty liver disease (NALFD), and steatohepatitis. Macrophages are the predominant immune cells in adipose tissues. Adipose tissue macrophages (ATMs) would switch to pro-inflammatory M1 state during obesity, causing local and systemic inflammation. However, the regulatory mechanism of ATMs has not yet been well described within this process. Using a high-fat diet (HFD)-induced mouse obesity model, we found that the costimulatory molecule CD226 was highly expressed on ATMs and knockout (KO) of CD226 alleviated obesity caused by HFD. Loss of CD226 reduced the accumulation of ATMs and hindered macrophage M1 polarization, with lower serum proinflammatory cytokine levels. Furthermore, deficiency of CD226 on ATMs decreased the phosphorylation levels of VAV1, AKT, and FOXO1 and thereby upregulated PPAR-γ. Further administration of PPAR-γ inhibitor restored M1 phenotype in CD226KO ATMs. In summary, loss of CD226 alleviates the HFD-induced obesity and systemic inflammation through inhibition of the accumulation and M1 polarization of ATMs in which PPAR-γ-dependent signaling pathway is involved, suggesting that CD226 may be identified as a potential molecular target for the clinical treatment of obesity.

Deficiency of platelet adhesion molecule CD226 causes megakaryocyte development and platelet hyperactivity.

This study used constitutive CD226 gene knockout (KO) mice as a model to investigate the functions and mechanisms of CD226 in megakaryocyte (MK) maturation and platelet activation. Although CD226 deficiency did not cause MK polyploidization or platelet granule abnormalities, increased MK counts were detected in the femora bone marrow (BM) and spleen of CD226 KO mice. Particularly, CD226 KO mice have a more extensive membrane system in MKs and platelets than wild-type (WT) mice. We also demonstrated that CD226 KO mice displayed increased platelet counts, shortened bleeding time, and enhanced platelet aggregation. CD226 KO platelets had an increased mature platelet ratio compared to the control platelets. In addition, the observed reduction in bleeding time may be due to decreased nitric oxide (NO) production in the platelets. Platelet-specific CD226-deficient mice showed similar increased MK counts, shortened bleeding time, enhanced platelet aggregation, and decreased NO production in platelets. Furthermore, we performed middle cerebral artery occlusion-reperfusion surgery on WT and CD226 KO mice to explore the potential effect of CD226 on acute ischemia-reperfusion injury; the results revealed that CD226 deficiency led to significantly increased infarct area. Thus, CD226 is a promising candidate for the treatment of thrombotic disorders.

Contributions of gains and losses to attentional capture and disengagement: evidence from the gap paradigm.

It is known that movements of visual attention are influenced by features in a scene, such as colors, that are associated with value or with loss. The present study examined the detailed nature of these attentional effects by employing the gap paradigm-a technique that has been used to separately reveal changes in attentional capture and shifting, and changes in attentional disengagement. In four experiments, participants either looked toward or away from stimuli with colors that had been associated either with gains or with losses. We found that participants were faster to look to colors associated with gains and slower to look away from them, revealing effects of gains on both attentional capture and attentional disengagement. On the other hand, participants were both slower to look to features associated with loss, and faster to look away from such features. The pattern of results suggested, however, that the latter finding was not due to more rapid disengagement from loss-associated colors, but instead to more rapid shifting of attention away from such colors. Taken together, the results reveal a complex pattern of effects of gains and losses on the disengagement, capture, and shifting of visual attention, revealing a remarkable flexibility of the attention system.

Protective CD8+ T-cell response against Hantaan virus infection induced by immunization with designed linear multi-epitope peptides in HLA-A2.1/Kb transgenic mice.

BACKGROUND: An effective vaccine that prevents disease caused by hantaviruses is a global public health priority, but up to now, no vaccine has been approved for worldwide use. Therefore, novel vaccines with high prophylaxis efficacy are urgently needed. METHODS: Herein, we designed and synthesized Hantaan virus (HTNV) linear multi-epitope peptide consisting of HLA-A*02-restricted HTNV cytotoxic T cell (CTL) epitope and pan HLA-DR-binding epitope (PADRE), and evaluated the immunogenicity, as well as effectiveness, of multi-epitope peptides in HLA-A2.1/Kb transgenic mice with interferon (IFN)-γ enzyme-linked immunospot assay, cytotoxic mediator detection, proliferation assay and HTNV-challenge test. RESULTS: The results showed that a much higher frequency of specific IFN-γ-secreting CTLs, high levels of granzyme B production, and a strong proliferation capacity of specific CTLs were observed in splenocytes of mice immunized with multi-epitope peptide than in those of a single CTL epitope. Moreover, pre-immunization of multi-epitope peptide could reduce the levels of HTNV RNA loads in the liver, spleen and kidneys of mice, indicating that specific CTL responses induced by multi-epitope peptide could reduce HTNV RNA loads in vivo. CONCLUSIONS: This study may provide an important foundation for the development of novel peptide vaccines for HTNV prophylaxis.

LAIR-1 overexpression inhibits epithelial-mesenchymal transition in osteosarcoma via GLUT1-related energy metabolism.

BACKGROUND: Leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) is a collagen receptor belonging to the immunoglobulin superfamily. Although previous studies have evaluated the biological role of LAIR in solid tumors, the precise mechanisms underlying the functions of LAIR-1 as a regulator of tumor biological functions remain unclear. METHODS: LAIR-1 expression was evaluated by immunohistochemical analysis using an osteosarcoma (OS) tissue microarray. Wound healing and transwell migration assays were performed to evaluate tumor cell migration. Quantitative real-time polymerase chain reaction (qPCR) and western blotting were conducted to detect the expression of epithelial-mesenchymal transition (EMT)-related molecules. RNA-sequencing (RNA-seq) was conducted to evaluate the mRNA expression profiles after overexpressing LAIR-1 in OS cells. Glucose transporter (Glut)1 expression in OS cells was evaluated by western blotting. RESULTS: LAIR-1 expression was significantly different between the T1 and T2 stages of OS tumors, and it inhibited OS cell migration. LAIR-1 expression was inversely correlated with the expression of Twist1, an EMT-associated transcription factor, via the Forkhead box O1 signal transduction pathway. Furthermore, RNA-seq and qPCR demonstrated that the expression of EMT energy metabolism-related molecules was significantly reduced after LAIR-1 overexpression. CONCLUSIONS: LAIR-1 overexpression decreased the expression of Glut1 and inhibited the expression of EMT-related molecules in OS cells. These findings provide new insights into the molecular mechanism underlying OS progression.

ADAR1 attenuates allogeneic graft rejection by suppressing miR-21 biogenesis in macrophages and promoting M2 polarization.

ADAR1 (adenosine deaminase acting on double-stranded RNA 1) is an RNA-editing enzyme that mediates adenosine-to-inosine RNA editing events, an important post-transcriptional modification mechanism that can alter the coding properties of mRNA or regulate microRNA biogenesis. ADAR1 also regulates the innate immune response. Here, we have demonstrated that ADAR1 expression increased in LPS-stimulated macrophages. Silencing ADAR1 by using small interfering RNA in macrophages resulted in the pronounced polarization of macrophages to M1, whereas ADAR1 overexpression promoted M2 polarization, which indicated that ADAR1 can inhibit macrophage hyperpolarization and prevent immune hyperactivity. The RNA-RNP immunoprecipitation binding assay demonstrated a direct interaction between ADAR1 and miR-21 precursor. Significant up-regulation in IL-10 and down-regulation in miR-21 were observed in ADAR1-overexpressing macrophages. We evaluated miR-21 target mRNAs and macrophage polarization signaling pathways and found that forkhead box protein O1 (Foxo1) was up-regulated in cells that overexpressed ADAR1. In a mouse allogeneic skin transplantation model, grafts in the ADAR1-overexpressed group survived longer and suffered less immune cell infiltration. In ADAR1-overexpressed recipients, splenic macrophages were significantly polarized to M2, and levels of sera IL-10 were markedly higher than those in the control group. In summary, ADAR1 modulates macrophage M2 polarization via the ADAR1-miR-21-Foxo1-IL-10 axis, thereby suppressing allogeneic graft rejection.-Li, J., Xie, J., Liu, S., Li, X., Zhang, D., Wang, X., Jiang, J., Hu, W., Zhang, Y., Jin, B., Zhuang, R., Yin, W. ADAR1 attenuates allogeneic graft rejection by suppressing miR-21 biogenesis in macrophages and promoting M2 polarization.

Blocking CD226 Promotes Allogeneic Transplant Immune Tolerance and Improves Skin Graft Survival by Increasing the Frequency of Regulatory T Cells in a Murine Model.

BACKGROUND/AIMS: Regulatory T cells (Tregs) play key roles in maintaining peripheral tolerance and preventing autoimmune disease. Treg modulation could be helpful in treating malignancies, autoimmune disease, and allergies, as well as to facilitate organ transplantation. Signals transduced by co-stimulatory molecules are essential for Treg differentiation, homeostasis, and function. One well-known active receptor, CD226, also known as DNAM-1 or PTA1, is an adhesion molecule that interacts primarily with CD155 and is involved in Treg differentiation and immune tolerance to transplanted tissue. METHODS: Anti-CD226 monoclonal antibody (mAb) and truncated recombinant CD226 proteins were employed to manipulate the CD226 signal. Various T cell markers on freshly isolated splenocytes and T lymphocytes were characterized by flow cytometry Cell proliferation was measured by carboxyfluorescein succinimidyl ester dye, mRNA transcripts by q-RT PCR, and protein expression by western blotting. A BALB/c-to-C57BL/6 skin allograft model was used to determine the effects of CD226 blocking treatment. RESULTS: We observed that both intact extracellular domains of CD226 were necessary for functional interaction of the receptor with its ligand CD155, even though one domain was shown to bind CD155 with lower affinity in a solid binding assay. Importantly, CD226 mAb promoted Treg expansion in a mixed lymphocyte culture and inhibited the cytotoxicity of effector cells. In allogeneic skin transplant mice, administering CD226 mAb reduced inflammation and prolonged allogeneic graft survival, with an increase in the frequency of Tregs. CONCLUSIONS: Our results reveal the mechanism underlying CD226-CD155 interactions and indicate that CD226 signals can be manipulated to promote Treg expansion. Moreover, we provide new evidence that suggests the therapeutic potential of anti-CD226 with allogeneic transplantation.

TIGIT-Fc alleviates acute graft-versus-host disease by suppressing CTL activation via promoting the generation of immunoregulatory dendritic cells.

Graft-versus-host disease (GVHD) is the most common complication and major limitation of allogeneic hematopoietic stem cell transplantation. The CD226/TIGIT-CD155 signal is critical for the cross-talk between T cells and dendritic cells (DCs). Studies have shown that blockade of the CD226-CD155 interaction, using an anti-CD226 antibody, can significantly ameliorate GVHD. It has also been reported that a TIGIT-Fc fusion protein exerts immunosuppressive effects by binding to CD155 on DCs. Here, we used a mouse allogeneic acute GVHD model to explore the therapeutic potential and mechanism of action of TIGIT-Fc. C57/BL6 and Balb/c mice were used as hematopoietic cell graft donors and recipients, respectively. In the TIGIT-Fc-treated mice, GVHD symptom occurrence and mortality were delayed compared to that in isotype control group mice. Histopathological analyses revealed that following TIGIT-Fc treatment, liver and small intestine tissue damage was reduced with minimal lymphocytic infiltration. The percentage of CD8+IFN-γ+ and CD8+ granzyme B+ cells significantly decreased in the TIGIT-Fc group. Moreover, treatment with TIGIT-Fc, even after the onset of GVHD, ameliorated symptoms and prolonged survival. TIGIT-Fc also inhibited CD8+ T cell activation in vitro; this was dependent on the presence of CD155 on bone marrow-derived dendritic cells (BMDCs) and on IL-10 production. In addition, TIGIT-CD155 ligation triggered both Erk phosphorylation and STAT3 nuclear translocation. These data indicate that TIGIT plays an important role in the development of GVHD and is an ideal molecular target to treat acute GVHD.

Silencing LAIR-1 in human THP-1 macrophage increases foam cell formation by modulating PPARγ and M2 polarization.

Formation of macrophage-derived foam cells may mark the initial stages of atherosclerosis. We investigated the association between the expression of the leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1) in macrophages and foam cell formation. A foam cell model was established by incubating THP-1-derived macrophages and bone marrow macrophages (BMMs) with oxidized low-density lipoprotein (ox-LDL). The role of LAIR-1 in foam cell formation was evaluated via Oil Red O staining and Dil-ox-LDL fluorescence intensities. Peroxisome proliferator-activated receptor gamma (PPARγ), cholesterol metabolism-related genes, and the role of LAIR-1 in activating classically activated (M1) and alternatively activated (M2) macrophages were evaluated by qPCR. Additionally, activation of protein-tyrosine phosphatase-1 (SHP-1) and cAMP-response element binding protein (CREB) were detected by western blotting. Results indicated that silencing LAIR-1 in macrophages modulated the SHP-1/CREB/PPARγ pathway, thereby promoting M2 macrophage polarization and increasing foam cell formation. Therefore, Inhibition of LAIR-1 in macrophages may promote foam cell formation and atherosclerosis.