Class II Transactivator Expression Research Articles

Expression of HLA-DR by mesenchymal stromal cells in the platelet lysate era: an obsolete release criterion for MSCs?

BackgroundAccording to the definition of the International Society for Cell and Gene Therapy (ISCT), mesenchymal stromal cells (MSCs) do not express HLA-DR. This phenotypic marker as a release criterion for clinical use was established at a time when MSCs were expanded in fetal bovine serum (FBS)-containing media. Replacement of FBS with platelet lysate (PLs) as a medium supplement induced a significantly higher fraction of MSCs to express MHC class II antigens.MethodsAs this raised concerns that such MSCs may play the role of antigen-presenting cells for T cells, in the current study, we studied major factors that may induce HLA-DR on MSCs by means of flow cytometry and real-time polymerase chain reaction. The immunomodulatory potential of MSCs was assessed by a mixed lymphocyte reaction.ResultsOur results demonstrated that a very low percentage of generated and expanded MSCs in FBS express HLA-DR (median: 1.1%, range: 0.3–22%) compared to MSCs generated and expanded in PLs (median: 28.4%, range: 3.3–73.7%). Analysis of the cytokine composition of ten PLs showed a significant positive correlation between the levels of IL-1β, IL-4, IL-10, IL-17, bFGF and expression of HLA-DR, in contrast to no correlation with the age of MSC donors and HLA-DR (r = 0.21). Both MSCs expressing low and high levels of HLA-DR expressed class II transactivator (CIITA), a master gene coding for these molecules. Our results demonstrate for the first time that MSCs with constitutively high levels of HLA-DR also express moderate levels of indoleamine 2,3-dioxygenase (IDO). Treatment of MSCs with multiple doses of TGF-β1 at passage 0 (P0) and passage 1 (P1) completely abrogated HLA-DR and IDO expression. In contrast, treatment of MSCs with a single dose of TGF-β1 after P0 only partially reduced the expression of HLA-DR and CIITA. Remarkably, increased expression of HLA-DR on MSCs that constitutively express high levels of this antigen after overnight incubation with IFN-γ was rather unaffected by incubation with TGF-β1. However, treatment of MSCs with TGF-β1 for 24 h completely abrogated constitutive expression of IDO.ConclusionsIrrespective of HLA-DR expression at the population level, all MSC preparations significantly inhibited the proliferation of stimulated peripheral blood mononuclear cells, indicating that HLA-DR represents an obsolete release marker for the clinical use of MSCs.

Cancer-specific T helper shared and neo-epitopes uncovered by expression of the MHC class II master regulator CIITA.

We report an approach to identify tumor-specific CD4+ Tcell neo-epitopes of both mouse and human cancer cells by analysis of major histocompatibility complex (MHC) class II-eluted natural peptides. MHC class II-presented peptide sequences are identified by introducing the MHC class II transactivator (CIITA) in tumor cells that were originally MHC class II negative. CIITA expression facilitates cell-surface expression of MHC class II molecules and the appropriate peptide-loading machinery. Peptide elution of purified MHC class II molecules and subsequent mass spectrometry reveals oncoviral- and neo-epitopes as well as shared epitopes. Immunological relevance of these epitopes is shown by natural presentation by dendritic cells and immunogenicity. Synthetic peptide vaccination induced functional CD4+ Tcell responses, which helped tumor control invivo. Thus, this CIITA transfection approach aids to identify relevant T helper epitopes presented by any MHC class II allele that would be otherwise very difficult to predict and reveals important targets for cancer immunotherapy.

Chromatin-Remodeling Factor BRG1 Is a Negative Modulator of L. donovani in IFNγ Stimulated and Infected THP-1 Cells.

Intracellular pathogens manipulate the host cell for their own survival by contributing to modifications of host epigenome, and thus, altering expression of genes involved in the pathogenesis. Both ATP-dependent chromatin remodeling complex and histone modifications has been shown to be involved in the activation of IFNγ responsive genes. Leishmania donovani is an intracellular pathogen that causes visceral leishmaniasis. The strategies employed by Leishmania donovani to modulate the host epigenome in order to overcome the host defense for their persistence has been worked out in this study. We show that L. donovani negatively affects BRG1, a catalytic subunit of mammalian SWI/SNF chromatin remodeling complex, to alter IFNγ induced host responses. We observed that L. donovani infection downregulates BRG1 expression both at transcript and protein levels in cells stimulated with IFNγ. We also observed a significant decrease in IFNγ responsive gene, Class II transactivator (CIITA), as well as its downstream genes, MHC-II (HLA-DR and HLA-DM). Also, the occupancy of BRG1 at CIITA promoters I and IV was disrupted. A reversal in CIITA expression and decreased parasite load was observed with BRG1 overexpression, thus, suggesting BRG1 is a potential negative regulator for the survival of intracellular parasites in an early phase of infection. We also observed a decrease in H3 acetylation at the promoters of CIITA, post parasite infection. Silencing of HDAC1, resulted in increased CIITA expression, and further decreased parasite load. Taken together, we suggest that intracellular parasites in an early phase of infection negatively regulates BRG1 by using host HDAC1 for its survival inside the host.

DNA-double strand breaks enhance the expression of major histocompatibility complex class II through the ATM-NF-κΒ-IRF1-CIITA pathway.

Major histocompatibility complex class II (MHC II) is important for the adaptive immune response because MHC II presents processed antigens to a cluster of differentiation 4 (CD4)-positive T-cells. Conventional doses of chemotherapeutic agents induce tumor cell death by causing DNA double-strand breaks (DSBs). However, cellular responses caused by sub-lethal doses of chemotherapeutic agents are poorly understood. In this study, using low doses of chemotherapeutic agents, we showed that DSBs enhanced the expression of MHC II on cells that originate from antigen-presenting cells (APCs). These agents induced the MHC class II transactivator (CIITA), the master regulator of MHC II, and interferon regulatory factor 1 (IRF1), a transcription factor for CIITA. Short hairpin RNA against IRF1 suppressed chemotherapeutic agent-induced CIITA expression, whereas exogenous expression of IRF1 induced CIITA. Inhibition of ataxia-telangiectasia mutated (ATM), a DSB-activated kinase, suppressed induction of IRF1, CIITA, and MHC II. Similar results were observed by inhibiting NF-κB, a downstream target of ATM. These results suggest that DSBs induce MHC II activity via the ATM-NF-κB-IRF1-CIITA pathway in cells that intrinsically present antigens. Additionally, chemotherapeutic agents induced T-cell regulatory molecules. Our findings suggest that chemotherapeutic agents enhance the antigen presentation activity of APCs for T-cell activation.

The MHC Class II Transactivator CIITA: Not (Quite) the Odd-One-Out Anymore among NLR Proteins.

In this review, we discuss the major histocompatibility complex (MHC) class II transactivator (CIITA), which is the master regulator of MHC class II gene expression. CIITA is the founding member of the mammalian nucleotide-binding and leucine-rich-repeat (NLR) protein family but stood apart for a long time as the only transcriptional regulator. More recently, it was found that its closest homolog, NLRC5 (NLR protein caspase activation and recruitment domain (CARD)-containing 5), is a regulator of MHC-I gene expression. Both act as non-DNA-binding activators through multiple protein–protein interactions with an MHC enhanceosome complex that binds cooperatively to a highly conserved combinatorial cis-acting module. Thus, the regulation of MHC-II expression is regulated largely through the differential expression of CIITA. In addition to the well-defined role of CIITA in MHC-II GENE regulation, we will discuss several other aspects of CIITA functions, such as its role in cancer, its role as a viral restriction element contributing to intrinsic immunity, and lastly, its very recently discovered role as an inhibitor of Ebola and SARS-Cov-2 virus replication. We will briefly touch upon the recently discovered role of NLRP3 as a transcriptional regulator, which suggests that transcriptional regulation is, after all, not such an unusual feature for NLR proteins.

Cannabinoid receptors modulate LPS-induced increase of class-II transactivator expression levels in a microglial cell line

Microglial antigen generation (MAG) is an essential process in regulating disease states and homeostasis of the central nervous system. MAG is considered as responsible autoimmune mechanism in neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's diseases. Neuroprotective and regulator effects of cannabinoid receptors on these disease states and modulation with pharmacological agents are urgent subjects in recent decades. Although different aspects of microglial immune response have been investigated, specific effects of these receptor subtypes in the MAG are still unclear. Therefore, in the current study, we have investigated the effects of CB1 and CB2 receptors on antigen generation by investigating MHC-II and its master regulator CIITA by specific cannabinoid agents (ACEA, AM-251, CP 55,940, and SR144528) in the LPS-induced BV-2 cells. Additionally, the effects of drug treatments on inflammatory status were measured by determining IL-1β, IL-6, and TNF-α levels. LPS-induced increase in MHC-II and CIITA expression was inhibited by specific CB1 agonist, ACEA, and nonselective cannabinoid agonist CP 55,940. A combination with specific CB1 antagonist AM-251 prevented these inhibitory effects of ACEA and CP 55,940 on both MHC-II and CIITA expression. Although specific CB2 antagonist, SR144528, also prevented the inhibitory effect of CP 55,940 on MHC-II, it did not affect CIITA expression. LPS-induced IL-1β, IL-6, and TNF-α increase both attenuated with CP 55,940 and ACEA treatments. Although both selective cannabinoid antagonists inhibited this effect, preventive effects were more dominant on CB1 receptors. Our results demonstrated that CB1 receptors majorly mediates LPS-induced MHC-II and its regulator CIITA expression in microglial cells.

Link between CIITA rs3087456 polymorphism and the risk of laryngeal squamous cell carcinoma in a Chinese population

The class II trans-activator (CIITA) is the master regulator of the major histocompatibility complex (MHC) gene expression. CIITA mutations have been previously associated with several kinds of tumors, while the role of CIITA polymorphisms (rs3087456) in laryngeal squamous cell carcinoma (LSCC) is little known. We evaluate the link between CIITA polymorphisms and the existence of LSCC in patients. This study was conducted with 200 Chinese Han patients (LSCC) and 200 healthy control subjects.The association of CIITA genetic polymorphism rs3087456 with the risk of LSCC was assessed through pyrosequencing. The CIITA expression in LSCC tumor tissue and adjacent normal tissue was detected by immunohistochemistry (IHC) staining. The relationship between the genotype of rs3087456 in controls and in clinical pathology features in LSCC were analyzed, and in-silico analysis was also used for the CIITA gene. The in-silico analysis results showed that the CIITA gene is closely related to genes such as RFX5 and RFXAP. The IHC results showed that CIITA was highly expressed in LSCC tumor tissues, compared with the corresponding adjacent normal tissues. The AG, AG + AA, and A genotypes of rs3087456 of CIITA gene notably increased the risk of LSCC compared to the controls. Our study suggests that CIITA polymorphism (rs3087456) is associated with a higher risk of developing LSCC in a Chinese cohort.

Valproic acid promotes a decrease in mycobacterial survival by enhancing nitric oxide production in macrophages stimulated with IFN-γ

Tuberculosis is one of the leading causes of mortality worldwide, it is caused by Mycobacterium tuberculosis (Mtb), a bacteria that employs several strategies to evade the host immune response. For instance, Mtb interferes with the overexpression of class II transactivator (CIITA) in macrophages exposed to IFN-γ by inhibiting histone acetylation at its promoter, which can be reverted by the histone deacetylase inhibitor (HDACi) sodium butyrate. In this work, we evaluated whether a different HDACi, valproic acid (VPA), could revert the inhibition of gene expression induced by Mtb. J774 macrophages treated with VPA and IFN-γ unexpectedly induced a higher expression of the inducible nitric oxide synthase and a higher production of nitric oxide when exposed to the 19 kDa lipoprotein of Mtb or the whole bacteria. However, VPA was unable to revert the inhibition of CIITA expression induced by the 19 kDa lipoprotein of Mtb. Finally, macrophages infected with Mtb and treated with VPA and IFN-γ showed a significant reduction in intracellular bacteria. Our findings suggest a new therapeutic potential of VPA for the treatment of tuberculosis.

Fowlpoxvirus recombinants coding for the CIITA gene increase the expression of endogenous MHC-II and Fowlpox Gag/Pro and Env SIV transgenes.

A complete eradication of an HIV infection has never been achieved by vaccination and the search for new immunogens that can induce long-lasting protective responses is ongoing. Avipoxvirus recombinants are host-restricted for replication to avian species and they do not have the undesired side effects induced by vaccinia recombinants. In particular, Fowlpox (FP) recombinants can express transgenes over long periods and can induce protective immunity in mammals, mainly due to CD4-dependent CD8+ T cells. In this context, the class II transactivator (CIITA) has a pivotal role in triggering the adaptive immune response through induction of the expression of class-II major histocompatibility complex molecule (MHC-II), that can present antigens to CD4+ T helper cells. Here, we report on construction of novel FPgp and FPenv recombinants that express the highly immunogenic SIV Gag-pro and Env structural antigens. Several FP-based recombinants, with single or dual genes, were also developed that express CIITA, driven from H6 or SP promoters. These recombinants were used to infect CEF and Vero cells in vitro and determine transgene expression, which was evaluated by real-time PCR and Western blotting. Subcellular localisation of the different proteins was evaluated by confocal microscopy, whereas HLA-DR or MHC-II expression was measured by flow cytometry. Fowlpox recombinants were also used to infect syngeneic T/SA tumour cells, then injected into Balb/c mice to elicit MHC-II immune response and define the presentation of the SIV transgene products in the presence or absence of FPCIITA. Antibodies to Env were measured by ELISA. Our data show that the H6 promoter was more efficient than SP to drive CIITA expression and that CIITA can enhance the levels of the gag/pro and env gene products only when infection is performed by FP single recombinants. Also, CIITA expression is higher when carried by FP single recombinants than when combined with FPgp or FPenv constructs and can induce HLA-DR cell surface expression. However, in-vivo experiments did not show any significant increase in the humoral response. As CIITA already proved to elicit immunogenicity by improving antigen presentation, further in-vivo experiments should be performed to increase the immune responses. The use of prime/boost immunisation protocols and the oral administration route of the recombinants may enhance the immunogenicity of Env peptides presented by MHC-II and provide CD4+ T-cell stimulation.

P127 Unexpected negative crossmatch in a patient with high level ANTI-HLA-DQA donor specific antibodies

In 2014 OPTN/UNOS approved a policy to include DQA1 as part of the allocation process but the effect of preformed DQA donor specific antibody (DSA) on graft survival is not fully understood. We present a case of a negative flow cytometric crossmatch (FXCM) and good graft survival in a patient with preformed DQA DSA, suggesting that DQ expression affects the impact of these antibodies. A 43 year old male presented for renal re-transplant and evaluation by single antigen beads revealed antibodies against DQ 2 and DQA 4, 5, & 6 (Table 1). A virtual crossmatch (VXM) with a deceased donor was incompatible due anti-DQA 5 DSA at ∼ 23,000MFI. A FCXM was, surprisingly, compatible on three serum dates tested. DSA testing 24 h post-transplant revealed anti-DQA 5 at ∼ 20,000 MFI. C1q testing revealed anti-DQA 5 at ∼ 31,000MFI. Confirmatory typing and a repeat FCXM were consistent with initial testing. A surrogate FCXM with a DQA 5 donor was B-cell positive (502 MCS [cutoff 270 MCS]). At day 3, the patient had delayed graft function with creatinine of 14.3 mg/dL. However, a biopsy showed no evidence of rejection and C4d staining was negative. At day 49, the creatinine had decreased to 2.27 mg/dL and the biopsy remained negative. The patient continues to have good graft function two years post-transplant. DQ is differentially expressed primarily through the class II transactivator (CIITA) pathway. The CIITA-PIII promoter drives constitutive expression of CIITA in B cells and can be activated by IFN γ in non-B cells. Epigenetic changes in CIITA-PIII can result in complete abrogation of CIITA and, consequently, DQ expression. It is possible that downregulation of CIITA in this donor resulted in minimal DQ expression in the graft. Due to the incompatibility of the VXM this patient could have been denied the benefits of transplantation. Studies of DQ expression are limited in transplantation and should be an area of increasing investigation as the ability to identify acceptably mismatched organs continues to advance. Download : Download high-res image (147KB) Download : Download full-size image

MicroRNA-146a reduces MHC-II expression via targeting JAK/STAT signaling in dendritic cells after stem cell transplantation.

Acute Graft-versus-host disease (GVHD) is a major immunological complication after allogeneic hematopoietic cell transplantation and a better understanding of the molecular regulation of the disease could help to develop novel targeted therapies. Here we found that a G/C polymorphism within the human microRNA-146a (miR-146a) gene of transplant-recipients, which causes reduced miR-146a levels, was strongly associated with the risk of developing severe acute GVHD (n=289). In mice, deficiency of miR-146a in the hematopoietic system or transfer of recipient-type miR 146a-/- dendritic cells (DCs) enhanced GVHD, while miR-146a mimic-transfected-DCs ameliorated disease. Mechanistically, lack of miR-146a enhanced JAK2 STAT1-pathway activity, which led to higher expression of class II-transactivator (CIITA) and consecutively increased MHCII-levels on DCs. Inhibition of JAK1/2 or CIITA knockdown in DCs prevented miR-146a-/- DC-induced GVHD exacerbation. Consistent with our findings in mice, patients with the miR-146a polymorphism rs2910164 in hematopoietic cells displayed higher MHCII levels on monocytes, which could be targeted by JAK1/2-inhibition.Our findings indicate that the miR-146a polymorphism rs2910164 identifies patients at high risk for GVHD before allo HCT. Functionally we show that miR-146a acts as a central regulator of recipient-type DC activation during GVHD by dampening the pro-inflammatory JAK-STAT/CIITA/MHCII axis, which provides a scientific rationale for early JAK1/2-inhibition in selected patients.

Development of potent class II transactivator gene delivery systems capable of inducing de novo MHC II expression in human cells, in vitro and ex vivo.

Class II transactivator (CIITA) induces transcription of major histocompatibility complex (MHC) II genes and can potentially be used to improve genetic immunotherapies by converting non-immune cells into cells capable of presenting antigens to CD4+ T cells. However, CIITA expression is tightly controlled and it remains unclear whether distinct non-immune cells differ in this transactivator regulation. Here we describe the development of gene delivery systems capable of promoting the efficient CIITA expression in non-immune cell lines and in primary human cells of an ex vivo skin explant model. Different human cell types undergoing CIITA overexpression presented high-level de novo expression of MHC II, validating the delivery systems as suitable tools for the CIITA evaluation as a molecular adjuvant for gene therapies.

Mycobacterium tuberculosis EsxL inhibits MHC-II expression by promoting hypermethylation in class-II transactivator loci in macrophages

Mycobacterium tuberculosis is known to modulate the host immune responses to facilitate its persistence inside the host cells. One of the key mechanisms includes repression of class-II transactivator (CIITA) and MHC-II expression in infected macrophages. However, the precise mechanism of CIITA and MHC-II down-regulation is not well studied. M. tuberculosis 6-kDa early secretory antigenic target (ESAT-6) is a known potent virulence and antigenic determinant. The M. tuberculosis genome encodes 23 such ESAT-6 family proteins. We herein report that M. tuberculosis and M. bovis bacillus Calmette-Guérin infection down-regulated the expression of CIITA/MHC-II by inducing hypermethylation in histone H3 lysine 9 (H3K9me2/3). Further, we showed that M. tuberculosis ESAT-6 family protein EsxL, encoded by Rv1198, is responsible for the down-regulation of CIITA/MHC-II by inducing H3K9me2/3. We further report that M. tuberculosis esxL induced the expression of nitric-oxide synthase, NO production, and p38 MAPK pathway, which in turn was responsible for the increased H3K9me2/3 in CIITA via up-regulation of euchromatic histone-lysine N-methyltransferase 2 (G9a). In contrast, inhibition of nitric-oxide synthase, p38 MAPK, and G9a abrogated H3K9me2/3, resulting in increased CIITA expression. A chromatin immunoprecipitation assay confirmed that hypermethylation at the promoter IV region of CIITA is mainly responsible for CIITA down-regulation and subsequent antigen presentation. We found that co-culture of macrophages infected with esxL-expressing M. smegmatis and mouse splenocytes led to down-regulation of IL-2, a key cytokine involved in T-cell proliferation. In summary, we demonstrate that M. tuberculosis EsxL inhibits antigen presentation by enhancing H3K9me2/3 at the CIITA promoter, thereby repressing its expression through NO and p38 MAPK activation.

Recombinant Lipoprotein Rv1016c Derived from Mycobacterium tuberculosis Is a TLR-2 Ligand that Induces Macrophages Apoptosis and Inhibits MHC II Antigen Processing.

TLR2-dependent cellular signaling in Mycobacterium tuberculosis-infected macrophages causes apoptosis and inhibits class II major histocompatibility complex (MHC-II) molecules antigen processing, leading to evasion of surveillance. Mycobacterium tuberculosis (MTB) lipoproteins are an important class of Toll-like receptor (TLR) ligand, and identified as specific components that mediate these effects. In this study, we identified and characterized MTB lipoprotein Rv1016c (lpqT) as a cell wall associated-protein that was exposed on the cell surface and enhanced the survival of recombinants M. smegmatis_Rv1016c under stress conditions. We found that Rv1016c lipoprotein was a novel TLR2 ligand and able to induce macrophage apoptosis in a both dose- and time-dependent manner. Additionally, apoptosis induced by Rv1016c was reserved in THP-1 cells blocked with anti-TLR-2 Abs or in TLR2−/− mouse macrophages, indicating that Rv1016c-induced apoptosis is dependent on TLR2. Moreover, we demonstrated that Rv1016c lipoprotein inhibited IFN-γ-induced MHC-II expression and processing of soluble antigens in a TLR2 dependent manner. Class II transactivator (CIITA) regulates MHC II expression. In this context, Rv1016c lipoprotein diminished IFN-γ-induced expression of CIITA IV through TLR2 and MAPK Signaling. TLR2-dependent apoptosis and inhibition of MHC-II Ag processing induced by Rv1016c during mycobacteria infection may promote the release of residual bacilli from apoptotic cells and decrease recognition by CD4+ T cells. These mechanisms may allow intracellular MTB to evade immune surveillance and maintain chronic infection.

HIC1 epigenetically represses CIITA transcription in B lymphocytes

Differentiation of B lymphocytes into isotope-specific plasma cells represents a hallmark event in adaptive immunity. During B cell maturation, expression of the class II transactivator (CIITA) gene is down-regulated although the underlying epigenetic mechanism is not completely defined. Here we report that hypermethylated in cancer 1 (HIC1) was up-regulated in differentiating B lymphocytes paralleling CIITA repression. Over-expression of HIC1 directly repressed endogenous CIITA transcription in B cells. Reporter assay and chromatin immunoprecipitation (ChIP) assay confirmed that HIC1 bound to the proximal CIITA type III promoter (−545/−113); mutation of a conserved HIC1 site within this region abrogated CIITA trans-repression. More important, depletion of HIC1 with small interfering RNA (siRNA) restored CIITA expression in differentiating B cells. Mechanistically, HIC1 preferentially interacted with and recruited DNMT1 and DNMT3b to the CIITA promoter to synergistically repress CIITA transcription. On the contrary, silencing of DNMT1/DNMT3b or inhibition of DNMT activity with 5-aza-dC attenuated CIITA trans-repression. Therefore, our data identify HIC1 as a novel factor involved in B cell differentiation acting as an epigenetic repressor of CIITA transcription.

Class II transactivator knockdown limits major histocompatibility complex II expression, diminishes immune rejection, and improves survival of allogeneic bone marrow stem cells in the infarcted heart.

This study was performed to investigate how to overcome immunorejection associated with allogeneic stem cell therapy in the infarcted heart. Allogeneic bone marrow mesenchymal stem cell (MSC) differentiation increases major histocompatibility complex II (MHC II) expression, inducing transition from immunoprivileged to immunogenic phenotype. MHC II expression is regulated by the class II transactivator (CIITA). We isolated and characterized mouse and human MSCs and knocked down CIITA expression. Wild-type (WT) or CIITA-knockout (CIITA(-)) mouse MSCs were implanted into infarcted mouse myocardia, and recipient allo-antibody formation, cell survival, and cardiac function were measured. WT mouse and human MSCs that were myogenically differentiated showed increased MHC II and CIITA expression. Differentiated CIITA(-) MSCs lacked MHC II induction and showed reduced cytotoxicity in allogeneic leukocyte coculture. Differentiation of human MSCs increased MHC II expression, which resulted in cytotoxicity in allogeneic leukocyte coculture and was prevented by CIITA small interfering RNA. In contrast to WT MSCs, CIITA(-) MSCs did not initiate recipient allo-antibody formation and instead survived in the injured myocardium and significantly improved ventricular function. Decreasing CIITA expression in allogeneic MSCs abolished MHC II induction during myogenic differentiation and prevented immunorejection of these cells from the infarcted myocardium, which enhanced beneficial functional effects of MSC implantation on myocardial repair.-Huang, X.-P., Ludke, A., Dhingra, S., Guo, J., Sun, Z., Zhang, L., Weisel, R. D., Li, R.-K. Class II transactivator knockdown limits major histocompatibility complex II expression, diminishes immune rejection, and improves survival of allogeneic bone marrow stem cells in the infarcted heart.

Mycobacterial esat-6 like protein alters antigen presentation and mediates intracellular survival in a NO and P38 dependent manner

Background: Early secretory antigenic target (Esat-6) protein coded by esxA is known for its significant role in virulence and T-cell antigenic determination for Tuberculosis. There are at least 23 such ESAT-6 family proteins encoded in Mycobacterium tuberculosis genome; and many of their functions remains uncharacterized. Here we investigated a mechanism by which a member of Mtb ESAT-6 like family proteins alters antibacterial defense mechanism of macrophages by blocking antigen presentation and on the other hand facilitates bacterial persistence inside the macrophages. Methods & Materials: Mtb esat-6 like protein (Esl) gene was overexpressed in Mycobacterium smegmatis (MsmEsl) using shuttle vector pSMT3. The role of MsmEsl in intracellular survival was checked by Colony forming unit (CFU) assay. Nitric oxide production was checked by using Griess reagent and iNOS expression by Realtime PCR, Western blotting and Immunofluorescence microscopy. Expression of MHC-II was checked by Flow cytometry analysis; Realtime PCR and Western blotting. The expression of CIITA which is the major transactivator of MHC-II was checked by Western blotting and Realtime PCR. Activation of MAPK signaling was checked by western blotting. To check the involvement of MAPK and iNOS in intracellular survival and alteration of antigen presentation, intracellular survival and CIITA expression after iNOS, P38 and ERK inhibition was checked by CFU assay and Western blotting respectively. Results: MsmEsl showed significantly increased intracellular survival in both THP-1 and RAW264.7 cells after 24h of infection. RAW264.7 macrophages infected with MsmEsl strain showed increased NO production and iNOS expression. Macrophages infected with MsmEsl showed decreased MHC-II expression. Similarly, down-regulation of CIITA (Class II transactivator) was also observed in MsmEsl infected macrophages. Cells infected with MsmEsl showed activation of P38 and ERK. Inhibition of ERK, P38 and iNOS decreased intracellular survival. Furthermore, when P38 and iNOS were inhibited, the CIITA level was increased. Conclusion: The present study highlights the role of an Esat-6 like protein in intracellular survival and alteration of Antigen presenting molecules in macrophages. It mediated intracellular survival and down regulated antigen presentation components by inducing NO production and P38 activation. Altogether this study can help in a better understanding of Mycobacterial pathogenesis.

A2b adenosine signaling represses CIITA transcription via an epigenetic mechanism in vascular smooth muscle cells

Chronic inflammation plays a major role in the pathogenesis of atherosclerosis. Vascular smooth muscle cells (VSMC), by expressing and presenting major histocompatibility complex II (MHC II) molecules, help recruit T lymphocyte and initiate the inflammatory response within the vasculature. We have previously shown that VSMCs isolated from mice with deficient adenosine A2b receptor (A2b-null) exhibit higher expression of class II transactivator (CIITA), the master regulator of MHC II transcription, compared to wild type littermates. Here we report that activation of A2b adenosine signaling suppresses CIITA expression in human aortic smooth muscle cells. Down-regulation of CIITA expression was largely attributable to transcriptional repression of type III and IV promoters. Chromatin immunoprecipitation (ChIP) analyses revealed that A2b signaling repressed CIITA transcription by attenuating specific histone modifications on the CIITA promoters in a STAT1-dependent manner. STAT1 interacted with PCAF/GCN5, histone H3K9 acetyltransferases, and WDR5, a key component of the mammalian H3K4 methyltransferase complex, to activate CIITA transcription. A2b signaling prevented recruitment of PCAF/GCN5 and WDR5 to the CIITA promoters in a STAT1-dependent manner. In conclusion, our data suggest that adenosine A2b signaling represses CIITA transcription in VSMCs by manipulating the interaction between STAT1 and the epigenetic machinery.

Attenuation of allograft rejection by intragraft inhibition of class II transcativator in high responder rat liver transplantation.

Major histocompatibility complex-II (MHC-II) plays an important role in graft rejection and class II transactivator (CIITA) is the key regulator for MHC-II expression. The aim of this study was to determine the efficacy of intragraft inhibition of CIITA in attenuating liver transplant rejection. Three plasmids containing small hairpin RNA (shRNA) against rat CIITA (pCIITA-shRNA) and one control plasmid of pHK-shRNA were constructed. In vitro dendritic cell (DC) transfection and liver transfection via portal vein in donor rats (n = 8) by shRNA plasmids were performed to confirm the inhibitory effect of pCIITA-shRNA on CIITA expression. It showed that expressions of CIITA and MHC-II were significantly inhibited by pCIITA-shRNA in both DC in vitro and liver of donor rats in vivo (p < 0.05 vs. control pHK-shRNA treatment). pCIITA1-shRNA was proved to be the best inhibitor among three pCIITA-shRNAs and then used in high-responder rat liver transplantation model (DA donors-to-Lewis recipients). Transplant groups (n = 16/group) include untreated recipients transplanted with donor liver graft pretreated with either saline, or pHK-shRNA, or pCIITA1-shRNA. Cyclosporine-treated (10 mg/kg, im, day 0-7) recipients transplanted with unmodified liver grafts were used as no rejection control. The results showed that the recipient rats survived significantly longer in pCIITA1-shRNA-treated group with markedly attenuated liver graft rejection (p < 0.05 vs. saline and pHK-shRNA-treated groups). Furthermore, significantly decreased intragraft expressions of CIITA, MHC-II, IL-2, and IFN-γ were found in pCIITA1-shRNA-treated group (p < 0.05 vs. saline and pHK-shRNA-treated groups). This study suggests that intragraft inhibition of CIITA could be a novel strategy for attenuating graft rejection in liver transplantation.

Semaphorin 3A alters endothelial cell immunogenicity by regulating Class II transactivator activity circuits

Endothelial cells (ECs) play a pivotal role in the allogeneic immune response upon transplantation. Semaphorin 3A (Sema3A) was implicated in the modulation of EC growth, but its effects on immunogenicity were not previously investigated. ECs were transduced with a lentiviral vector encoding for the green fluorescence protein (GFP) sequence under the control of a Class II transactivator (CIITA)-dependent promoter. Upon stimulation of nonmodified ECs with recombinant Sema3A protein, mRNA and protein levels of CIITA, HLA-DR, and Sema3A receptors were evaluated. An enzyme-linked immunosorbent assay was developed to quantify Sema3A levels in the sera of kidney-transplanted patients. Sema3A stimulation of lentiviral vector encoding for the GFP sequence ECs caused a significant up regulation of the transgene expression, indicating an increase in CIITA levels. Stimulation of nonmodified ECs with Sema3A resulted in an up regulation of CIITA expression, which was associated with enhanced HLA-DR levels and an increase in alloreactive CD4+ T-cell proliferation. Sema3A receptor expression was enhanced by CIITA, establishing a positive feedback loop. Higher levels of Sema3A were observed in sera of patients presenting with organ rejection. This study links Sema3A signaling in ECs with increased CIITA levels and higher HLA-DR expression, resulting in CD4+ T-cell activation, which might have important implications for tissue and organ transplantation.