Class II transactivator: mastering the art of major histocompatibility complex expression

Interferon Regulatory Factors (IRF1, IRF4, IRF5, IRF7 and IRF9) in Sichuan taimen (Hucho bleekeri): Identification and Functional Characterization

Background/Objectives: Interferon regulatory factors (IRFs) are multifunctional transcription factors that play important roles in the transcriptional regulation of interferons and in the immune response to pathogens. Therefore, studying the interferon system in fish is highly relevant in the prevention and treatment of viral diseases. Methods: In this study, five IRF genes (IRF1, IRF4, IRF5, IRF7 and IRF9) were identified and characterized in Hucho bleekeri, and their expression profiles were determined after LPS and Poly(I:C) treatment. Results: These IRFs have typical DNA-binding domains and IRF-association domains. Amino acid sequence comparison revealed high homology between these IRFs and those of other vertebrates, with the highest homology being with other salmonid fish. Phylogenetic analysis revealed that these IRFs are divided into four subfamilies (IRF1, IRF3, IRF4 and IRF5), with both IRF4 and IRF9 belonging to the IRF4 subfamily. IRF genes were widely expressed in all of the tested tissues, with IRF1, IRF4 and IRF9 being highly expressed in the spleen and kidney and IRF5 and IRF7 highly expressed in the gonads. IRF1, IRF4 and IRF5 expression was induced at different time points post-LPS challenge. IRF7 and IRF9 expression in the spleen and head kidney was not significantly altered by LPS induction. Poly(I:C) treatment altered IRF expression more significantly than LPS treatment. Poly(I:C) significantly altered the spleen and head kidney expression of all five IRFs. Conclusions: These findings reveal the potential role of IRFs in the antiviral response of H. bleekeri and provide a reference for examining signal transduction pathways in the interferon system in fish.

The NLR family of innate immune and cell death sensors

Nucleotide-binding oligomerization domain (NOD)-like receptors, also known as nucleotide-binding leucine-rich repeat receptors (NLRs), are a family of cytosolic pattern recognition receptors that detect a wide variety of pathogenic and sterile triggers. Activation of specific NLRs initiates pro- or anti-inflammatory signaling cascades and the formation of inflammasomes-multi-protein complexes that induce caspase-1 activation to drive inflammatory cytokine maturation and lytic cell death, pyroptosis. Certain NLRs and inflammasomes act as integral components of larger cell death complexes-PANoptosomes-driving another form of lytic cell death, PANoptosis. Here, we review the current understanding of the evolution, structure, and function of NLRs in health and disease. We discuss the concept of NLR networks and their roles in driving cell death and immunity. An improved mechanistic understanding of NLRs may provide therapeutic strategies applicable across infectious and inflammatory diseases and in cancer.

Epstein-Barr virus: the mastermind of immune chaos

The Epstein-Barr virus (EBV) is a ubiquitous human pathogen linked to various diseases, including infectious mononucleosis and multiple types of cancer. To control and eliminate EBV, the host's immune system deploys its most potent defenses, including pattern recognition receptors, Natural Killer cells, CD8+ and CD4+ T cells, among others. The interaction between EBV and the human immune system is complex and multifaceted. EBV employs a variety of strategies to evade detection and elimination by both the innate and adaptive immune systems. This demonstrates EBV's mastery of navigating the complexities of the immunological landscape. Further investigation into these complex mechanisms is imperative to advance the development of enhanced therapeutic approaches with heightened efficacy. This review provides a comprehensive overview of various mechanisms known to date, employed by the EBV to elude the immune response, while establishing enduring latent infections or instigate its lytic replication.

Melatonin inhibits the formation of chemically induced experimental encapsulating peritoneal sclerosis through modulation of T cell differentiation by suppressing of NF-κB activation in dendritic cells

Encapsulating peritoneal sclerosis (EPS) is a severe complication of peritoneal dialysis (PD). Surgery is a therapeutic strategy for the treatment of complete intestinal obstruction. However, complete intestinal obstruction in long-term PD results in high mortality and morbidity rates after surgery. Immunopathogenesis participates in EPS formation: CD8, Th1, and Th17 cell numbers increased during the formation of EPS. The anti-inflammatory and immunomodulatory effects of melatonin may have beneficial effects on this EPS. In the present study, we determined that melatonin treatment significantly decreases the Th1 and Th17 cell populations in mice with EPS, decreases the production of IL-1β, TNF-α, IL-6, and IFN-γ, and increases the production of IL-10. The suppression of Th1 and Th17 cell differentiation by melatonin occurs through the inhibition of dendritic cell (DC) activation by affecting the initiation of the NF-κB signaling pathway in DCs. Our study suggests that melatonin has preventive potential against the formation of EPS in patients with PD.

The NLR gene family: from discovery to present day

The mammalian NLR gene family was first reported over 20 years ago, although several genes that were later grouped into the family were already known at that time. Although it is widely known that NLRs include inflammasome receptors and/or sensors that promote the maturation of caspase 1, IL-1β, IL-18 and gasdermin D to drive inflammation and cell death, the other functions of NLR family members are less well appreciated by the scientific community. Examples include MHC class II transactivator (CIITA), a master transcriptional activator of MHC class II genes, which was the first mammalian NBD-LRR-containing protein to be identified, and NLRC5, which regulates the expression of MHC class I genes. Other NLRs govern key inflammatory signalling pathways or interferon responses, and several NLR family members serve as negative regulators of innate immune responses. Multiple NLRs regulate the balance of cell death, cell survival, autophagy, mitophagy and even cellular metabolism. Perhaps the least discussed group of NLRs are those with functions in the mammalian reproductive system. The focus of this Review is to provide a synopsis of the NLR family, including both the intensively studied and the underappreciated members. We focus on the function, structure and disease relevance of NLRs and highlight issues that have received less attention in the NLR field. We hope this may serve as an impetus for future research on the conventional and non-conventional roles of NLRs within and beyond the immune system.

The NLR member CIITA: Master controller of adaptive and intrinsic immunity and unexpected tool in cancer immunotherapy

Human nucleotide-binding oligomerization domain (NOD)-like receptors (NLR) include a large family of proteins that have important functions in basic physio-pathological processes like inflammation, cell death and regulation of transcription of key molecules for the homeostasis of the immune system. They are all characterized by a common backbone structure (the STAND ATPase module consisting in a nucleotide-binding domain (NBD), an helical domain 1 (HD1) and a winged helix domain (WHD), used by both prokaryotes and eukaryotes as defense mechanism. In this review, we will focus on the MHC class II transactivator (CIITA), the master regulator of MHC class II (MHC-II) gene expression and the founding member of NLR. Although a consistent part of the described NLR family components is often recalled as innate or intrinsic immune sensors, CIITA in fact occupies a special place as a unique example of regulator of both intrinsic and adaptive immunity. The description of the discovery of CIITA and the genetic and molecular characterization of its expression will be followed by the most recent studies that have unveiled this dual role of CIITA, key molecule in intrinsic immunity as restriction factor for human retroviruses and precious tool to induce the expression of MHC-II molecules in cancer cells, rendering them potent surrogate antigen presenting cells (APC) for their own tumor antigens.

Case report: A late and isolated presentation of meningoencephalomyelitis uncovers a novel pathogenic variant in the CIITA gene

Background

Bare lymphocyte syndrome type II (BLS II) is a rare form of severe combined immunodeficiency caused by mutations in the CIITA gene, which regulates major histocompatibility complex class II (MHC II) expression.

Objective

We report the case of a Saudi boy with a novel mutation in the CIITA gene who presented with acute and late meningoencephalomyelitis, resulting in severe neurodevelopmental regression.

Methods

We reviewed the patient's clinical and laboratory data obtained from medical records and performed a literature search on BLS II.

Results

The patient presented with acute meningoencephalomyelitis confirmed by MRI findings and was later found to carry a homozygous pathogenic variant in the CIITA gene p.(Leu473Hisfs*15). The patient had no MCH II expression, confirming the genetic diagnosis of autosomal recessive BLS II. Surprisingly, the patient's prior clinical history was unremarkable for significant infections or autoimmunity.

Conclusions

We report a case with a novel CIITA gene mutation presenting atypically with a late and isolated severe infection. Isolated severe meningoencephalomyelitis may be a manifestation of primary immunodeficiency.

The quest for effective immunotherapies against malignant peripheral nerve sheath tumors: Is there hope?

Immune-based therapies represent a new paradigm in the treatment of multiple cancers, where they have helped achieve durable and safe clinical responses in a growing subset of patients. While a wealth of information is available concerning the use of these agents in treating the more common malignancies, little has been reported about the use of immunotherapies against malignant peripheral nerve sheath tumors (MPNSTs), a rare form of soft tissue sarcoma that arises from the myelin sheaths that protect peripheral nerves. Surgical resection has been the mainstay of therapy in MPNSTs, but the recurrence rate is as high as 65%, and chemotherapy is generally ineffective. The immune contexture of MPNSTs, replete with macrophages and a varying degree of T cell infiltration, presents multiple opportunities to design meaningful therapeutic interventions. While preliminary results with macrophage-targeting strategies and oncolytic viruses are promising, identifying the subset of patients that respond to immune-based strategies will be a milestone. As part of our effort to help advance the use of immunotherapy for MPNSTs, here we describe recent insights regarding the immune contexture of MPNSTs, discuss emerging immune-based strategies, and provide a brief overview of potential biomarkers of response.

The Immunological Epigenetic Landscape of the Human Life Trajectory

Adaptive immunity changes over an individual’s lifetime, maturing by adulthood and diminishing with old age. Epigenetic mechanisms involving DNA and histone methylation form the molecular basis of immunological memory during lymphocyte development. Monocytes alter their function to convey immune tolerance, yet the epigenetic influences at play remain to be fully understood in the context of lifespan. This study of a healthy genetically homogenous cohort of children, adults and seniors sought to decipher the epigenetic dynamics in B-lymphocytes and monocytes. Variable global cytosine methylation within retro-transposable LINE-1 repeats was noted in monocytes compared to B-lymphocytes across age groups. The expression of the human leukocyte antigen (HLA)-DQ alpha chain gene HLA-DQA1*01 revealed significantly reduced levels in monocytes in all ages relative to B-lymphocytes, as well as between lifespan groups. High melting point analysis and bisulfite sequencing of the HLA-DQA1*01 promoter in monocytes highlighted variable cytosine methylation in children and seniors but greater stability at this locus in adults. Further epigenetic evaluation revealed higher histone lysine 27 trimethylation in monocytes from this adult group. Chromatin immunoprecipitation and RNA pulldown demonstrated association with a novel lncRNA TINA with structurally conserved similarities to the previously recognized epigenetic modifier PARTICLE. Seeking to interpret the epigenetic immunological landscape across three representative age groups, this study focused on HLA-DQA1*01 to expose cytosine and histone methylation alterations and their association with the non-coding transcriptome. Such insights unveil previously unknown complex epigenetic layers, orchestrating the strength and weakening of adaptive immunity with the progression of life.

Exacerbated immune response of the brain to peripheral immune challenge in post-septic mice

BACKGROUND

Mounting evidence indicates that sepsis can induce long-lasting brain dysfunction. Recently, it has been proposed that the brain may become more sensitive to systemic inflammation if microglial cells are already primed. Microglial priming has been demonstrated in aging, traumatic brain injury, and neurodegenerative diseases. There is evidence suggesting that systemic inflammation may also prime microglia. This study aimed to investigate the brain's response to a second immune challenge in sepsis survivors and the possible role of microglial priming.

METHODS

Adult BALB/c mice were intraperitoneally (ip) injected with 5 mg/kg lipopolysaccharide (LPS) for sepsis induction. One month later, mice received a second immune challenge (LPS, 0.33 mg/kg). A cohort of mice was sacrificed 2 h post-LPS injection to measure inflammatory mediators mRNA expression. The second cohort of mice was tested on a battery of behavioral tests and then sacrificed, and brain tissues were removed for biochemical analyses.

RESULTS

Results showed that in septic mice, secondary LPS challenge induced heightened neuroinflammation compared to the control mice, as evident by a significant increase of IL-1β, TNF-α, and iNOS mRNA expression. In the immunochallenged septic mice, the anti-inflammatory cytokine IL-10 expression was also significantly increased compared to the control mice. Sepsis induction significantly disrupted the recognition ability in the novel object recognition, but the second immune challenge had no significant effect. However, immunochallenged septic mice exhibited more anxiety-like behavior in the marble burying task and intensive depressive-like behavior in the forced swim test. Additionally, the second immune challenge reduced arginase-1 levels in septic but not control mice. On the other hand, CIITA levels were increased more significantly in the LPS injected control mice compared to septic mice. Neither sepsis nor the second immune challenge significantly affected inhibitory avoidance behavior and Aβ1-42 levels in brain tissue.

CONCLUSION

Our finding suggests that low-grade immune challenge can induce exacerbated behavioral change and exaggerated inflammatory response in the brain of post-septic mice.

Structural aspects of the MHC expression control system

The major histocompatibility complex (MHC) spans innate and adaptive immunity by presenting antigenic peptides to CD4⁺ and CD8⁺ T cells. Multiple transcription factors form an enhanceosome complex on the MHC promoter and recruit transcriptional machinery to activate gene transcription. Immune signals such as interferon-γ (IFN-γ) control MHC level by up-regulating components of the enhanceosome complex. As MHC plays crucial roles in immune regulation, alterations in the MHC enhanceosome structure will alter the pace of rapid immune responses at the transcription level and lead to various diseases related to the immune system. In this review, we discuss the current understanding of the MHC enhanceosome, with a focus on the structures of MHC enhanceosome components and the molecular basis of MHC enhanceosome assembly.

CIITA-Transduced Glioblastoma Cells Uncover a Rich Repertoire of Clinically Relevant Tumor-Associated HLA-II Antigens

CD4+ T cell responses are crucial for inducing and maintaining effective anticancer immunity, and the identification of human leukocyte antigen class II (HLA-II) cancer-specific epitopes is key to the development of potent cancer immunotherapies. In many tumor types, and especially in glioblastoma (GBM), HLA-II complexes are hardly ever naturally expressed. Hence, little is known about immunogenic HLA-II epitopes in GBM. With stable expression of the class II major histocompatibility complex transactivator (CIITA) coupled to a detailed and sensitive mass spectrometry-based immunopeptidomics analysis, we here uncovered a remarkable breadth of the HLA-ligandome in HROG02, HROG17, and RA GBM cell lines. The effect of CIITA expression on the induction of the HLA-II presentation machinery was striking in each of the three cell lines, and it was significantly higher compared with interferon gamma (IFNɣ) treatment. In total, we identified 16,123 unique HLA-I peptides and 32,690 unique HLA-II peptides. In order to genuinely define the identified peptides as true HLA ligands, we carefully characterized their association with the different HLA allotypes. In addition, we identified 138 and 279 HLA-I and HLA-II ligands, respectively, most of which are novel in GBM, derived from known GBM-associated tumor antigens that have been used as source proteins for a variety of GBM vaccines. Our data further indicate that CIITA-expressing GBM cells acquired an antigen presenting cell-like phenotype as we found that they directly present external proteins as HLA-II ligands. Not only that CIITA-expressing GBM cells are attractive models for antigen discovery endeavors, but also such engineered cells have great therapeutic potential through massive presentation of a diverse antigenic repertoire.

Role of Human Leukocyte Antigen System as A Predictive Biomarker for Checkpoint-Based Immunotherapy in Cancer Patients

Recent advances in cancer immunotherapy have clearly shown that checkpoint-based immunotherapy is effective in a small subgroup of cancer patients. However, no effective predictive biomarker has been identified so far. The major histocompatibility complex, better known in humans as human leukocyte antigen (HLA), is a very polymorphic gene complex consisting of more than 200 genes. It has a crucial role in activating an appropriate host immune response against pathogens and tumor cells by discriminating self and non-self peptides. Several lines of evidence have shown that down-regulation of expression of HLA class I antigen derived peptide complexes by cancer cells is a mechanism of tumor immune escape and is often associated to poor prognosis in cancer patients. In addition, it has also been shown that HLA class I and II antigen expression, as well as defects in the antigen processing machinery complex, may predict tumor responses in cancer immunotherapy. Nevertheless, the role of HLA in predicting tumor responses to checkpoint-based immunotherapy is still debated. In this review, firstly, we will describe the structure and function of the HLA system. Secondly, we will summarize the HLA defects and their clinical significance in cancer patients. Thirdly, we will review the potential role of the HLA as a predictive biomarker for checkpoint-based immunotherapy in cancer patients. Lastly, we will discuss the potential strategies that may restore HLA function to implement novel therapeutic strategies in cancer patients.

Recent Advances in Mouse Models of Sjögren's Syndrome

Sjögren's syndrome (SS) is a complex rheumatoid disease that mainly affects exocrine glands, resulting in xerostomia (dry mouth) and xerophthalmia (dry eye). SS is characterized by autoantibodies, infiltration into exocrine glands, and ectopic expression of MHC II molecules on glandular epithelial cells. In contrast to the well-characterized clinical and immunological features, the etiology and pathogenesis of SS remain largely unknown. Animal models are powerful research tools for elucidating the pathogenesis of human diseases. To date, many mouse models of SS, including induced models, in which disease is induced in mice, and genetic models, in which mice spontaneously develop SS-like disease, have been established. These mouse models have provided new insight into the pathogenesis of SS. In this review, we aim to provide a comprehensive overview of recent advances in the field of experimental SS.

Characterization of splenic MRC1hiMHCIIlo and MRC1loMHCIIhi cells from the monocyte/macrophage lineage of White Leghorn chickens

Monocytes/macrophages, which are found in a variety of organs, maintain tissue homeostasis at a steady state and act as the first line of defence during pathogen-induced inflammation in the host. Most monocyte/macrophage lineage studies in chickens have been largely performed using cell lines, while few studies using primary cells have been conducted. In the present study, the phenotypic and functional characteristics of splenic monocyte/macrophage lineage cells during steady state and inflammatory conditions were examined. Splenic monocyte/macrophage lineage cells could be identified as MRC1^loMHCII^hi and MRC1^hiMHCII^lo cells based on their surface expression of MRC1 and MHCII. In the steady state, MRC1^loMHCII^hi cells were more frequently found among MRC1⁺ cells. MRC1^loMHCII^hi cells expressed a higher number of antigen-presenting molecules (MHCII, MHCI, and CD80) than MRC1^hiMHCII^lo cells. In contrast, MRC1^hiMHCII^lo cells showed better phagocytic and CCR5-dependent migratory properties than MRC1^loMHCII^hi cells. Furthermore, MRC1^hiMHCII^lo cells infiltrated the spleen in vivo and then became MRC1^loMHCII^hi cells. During lipopolysaccharide (LPS)-induced inflammatory conditions that were produced via intraperitoneal (i.p.) injection, the proportion and absolute number of MRC1^hiMHCII^lo cells were increased in the spleen. Uniquely, inflammation induced the downregulation of MHCII expression in MRC1^hiMHCII^lo cells. The major source of inflammatory cytokines (IL-1β, IL-6, and IL-12) was MRC1^loMHCII^hi cells. Furthermore, MRC1^hiMHCII^lo cells showed greater bactericidal activity than MRC1^loMHCII^hi cells during LPS-induced inflammation. Collectively, these results suggest that two subsets of monocyte/macrophage lineage cells exist in the chicken spleen that have functional differences.

Helicobacter pylori Dampens HLA-II Expression on Macrophages via the Up-Regulation of miRNAs Targeting CIITA

Macrophages have a major role in infectious and inflammatory diseases, and the available data suggest that Helicobacter pylori persistence can be explained in part by the failure of the bacterium to be killed by professional phagocytes. Macrophages are cells ready to kill the engulfed pathogen, through oxygen-dependent and -independent mechanisms; however, their killing potential can be further augmented by the intervention of T helper (Th) cells upon the specific recognition of human leukocyte antigen (HLA)-II-peptide complexes on the surface of the phagocytic cells. As it pertains to H. pylori, the bacterium is engulfed by macrophages, but it interferes with the phagosome maturation process leading to phagosomes with an altered degradative capacity, and to megasomes, wherein H. pylori resists killing. We recently showed that macrophages infected with H. pylori strongly reduce the expression of HLA-II molecules on the plasma membrane and this compromises the bacterial antigen presentation to Th lymphocytes. In this work, we demonstrate that H. pylori hampers HLA-II expression in macrophages, activated or non-activated by IFN-γ, by down-regulating the expression of the class II major histocompatibility complex transactivator (CIITA), the "master control factor" for the expression of HLA class II genes. We provided evidence that this effect relies on the up-regulation of let-7f-5p, let-7i-5p, miR-146b-5p, and -185-5p targeting CIITA. MiRNA expression analysis performed on biopsies from H. pylori-infected patients confirmed the up-regulation of let-7i-5p, miR-146b-5p, and -185-5p in gastritis, in pre-invasive lesions, and in gastric cancer. Taken together, our results suggest that specific miRNAs may be directly involved in the H. pylori infection persistence and may contribute to confer the risk of developing gastric neoplasia in infected patients.

Autoimmune Addison's disease

Primary adrenal insufficiency (PAI) occurs in 1/5000-1/7000 individuals in the general population. Autoimmune Addison's disease (AAD) is the major cause of PAI and is a major component of autoimmune polyendocrine syndrome type 1 (APS1) and type 2 (APS2). Presence of 21-hydroxylase autoantibodies (21OHAb) identifies subjects with ongoing clinical or pre-clinical adrenal autoimmunity. AAD requires life-long substitutive therapy with two-three daily doses of hydrocortisone (HC) (15-25 mg/day) or one daily dose of dual-release HC and with fludrocortisone (0.5-2.0 mg/day). The lowest possible HC dose must be identified according to clinical and biochemical parameters to minimize long-term complications that include osteoporosis and cardiovascular and metabolic alterations. Women with AAD have lower fertility and parity as compared to age-matched healthy controls. Patients must be educated to double-triple HC dose in the case of fever or infections and to switch to parenteral HC in the case of vomiting, diarrhoea or acute hypotension.

NOD-like receptor signaling in inflammation-associated cancers: From functions to targeted therapies

BACKGROUND

Recently, many studies have reported that some botanicals and natural products were able to regulate NOD-like receptor signaling. NOD-like receptors (NLRs) have been established as crucial regulators in inflammation-associated tumorigenesis, angiogenesis, cancer cell stemness and chemoresistance. NLRs specifically sense pathogen-associated molecular patterns and respond by activating other signaling regulators, including Rip2 kinase, NF-κB, MAPK and ASC/caspase-1, leading to the secretion of various cytokines.

PURPOSE

The aim of this article is to review the molecular mechanisms of NOD-like receptor signaling in inflammation-associated cancers and the NLRs-targeted botanicals and synthetic small molecules in cancer intervention.

RESULTS

Aberrant activation of NLRs occurs in various cancers, orchestrating the tissue microenvironment and potentiating neoplastic risk. Blocking NLR inflammasome activation by botanicals or synthetic small molecules may be a valuable way to prevent cancer progression. Moreover, due to the roles of NLRs in regulating cytokine production, NLR signaling may be correlated with senescence-associated secretory phenotype.

CONCLUSION

In this review, we discuss how NLR signaling is involved in inflammation-associated cancers, and highlight the NLR-targeted botanicals and synthetic small molecules in cancer intervention.

CIITA-Driven MHC Class II Expressing Tumor Cells as Antigen Presenting Cell Performers: Toward the Construction of an Optimal Anti-tumor Vaccine

Construction of an optimal vaccine against tumors relies on the availability of appropriate tumor-specific antigens capable to stimulate CD4+ T helper cells (TH) and CD8+ cytolytic T cells (CTL). CTL are considered the major effectors of the anti-tumor adaptive immune response as they recognize antigens presented on MHC class I (MHC-I) molecules usually expressed in all cells and thus also in tumors. However, attempts to translate in clinics vaccination protocols based only on tumor-specific MHC-I-bound peptides have resulted in very limited, if any, success. We believe failure was mostly due to inadequate triggering of the TH arm of adaptive immunity, as TH cells are necessary to trigger and maintain the proliferation of all the immune effector cells required to eliminate tumor cells. In this review, we focus on a novel strategy of anti-tumor vaccination established in our laboratory and based on the persistent expression of MHC class II (MHC-II) molecules in tumor cells. MHC-II are the restricting elements of TH recognition. They are usually not expressed in solid tumors. By genetically modifying tumor cells of distinct histological origin with the MHC-II transactivator CIITA, the physiological controller of MHC-II gene expression discovered in our laboratory, stable expression of all MHC class II genes was obtained. This resulted in tumor rejection or strong retardation of tumor growth in vivo in mice, mediated primarily by tumor-specific TH cells as assessed by both depletion and adoptive cell transfer experiments. Importantly these findings led us to apply this methodology to human settings for the purification of MHC-II-bound tumor specific peptides directly from tumor cells, specifically from hepatocarcinomas, and the construction of a multi-peptide (MHC-II and MHC-I specific) immunotherapeutic vaccine. Additionally, our approach unveiled a noticeable exception to the dogma that dendritic cells are the sole professional antigen presenting cells (APC) capable to prime naïve TH cells, because CIITA-dependent MHC-II expressing tumor cells could also perform this function. Thus, our approach has served not only to select the most appropriate tumor specific peptides to activate the key lymphocytes triggering the anti-tumor effector functions but also to increase our knowledge of intimate mechanisms governing basic immunological processes.

ERβ-selective agonist alleviates inflammation in a multiple sclerosis model via regulation of MHC II in microglia

Multiple sclerosis (MS) is an autoimmune, demyelinating, and neurodegenerative disease of the central nervous system (CNS) that affects 2-2.5 million people worldwide. Although the etiology of MS is not well known, MS is widely considered to be an autoimmune disease. Currently approved MS drugs reduce relapse rates but fail to reverse or prevent neurodegeneration and disability progression. Increasing evidence indicates that microglia and major histocompatibility complex class II (MHC II) expression in these cells play important roles in the pathophysiology of MS. For a T cell to contribute to CNS pathogenesis, it must be reactivated by antigen-presenting cells within the CNS parenchyma. Susceptibility to MS is associated with MHC II genes, suggesting that presentation of antigens on MHC II plays an important role in CD4+ T-cell reactivation and disease initiation. An ERβ-selective agonist was previously reported to suppress reactivation of T cells invading the spinal cord, thereby reducing the severity of symptoms and decreasing mortality in the first 2 weeks after disease onset. However, the mechanism by which the expression of MHC II in microglia is regulated by ERβ-selective agonists is still unclear. Therefore, we hypothesize that ERβ-selective agonists inhibit MHC II expression in microglia via inhibition of class II trans-activator (CIITA) expression by a mechanism involving inhibition of the translocation of IFNγ regulatory factor (IRF-1) to the nucleus, thereby inhibiting the inflammatory response and symptoms in the MS model.

Interferon Regulatory Factors 1 and 2 Play Different Roles in MHC II Expression Mediated by CIITA in Grass Carp, Ctenopharyngodon idella

Expression of major histocompatibility complex class II (MHC II) molecules, which determines both the immune repertoire during development and subsequent triggering of immune responses, is always under the control of a unique (MHC class II) transactivator, CIITA. The IFN-γ-inducible MHC II expression has been extensively and thoroughly studied in humans, but not in bony fish. In this study, the characterization of CIITA was identified and its functional domains were analyzed in grass carp. The absence of GAS and E-box in the promoter region of grass carp CIITA, might imply that the cooperative interaction between STAT1 and USF1 to active the CIITA expression, found in mammals, is not present in bony fish. After the transfection of IFN-γ or IFN-γ rel, only IFN-γ could induce MHC II expression mediated by CIITA. Moreover, interferon regulatory factor (IRF) 2, which cooperates with IRF1 to active the CIITA promoter IV expression in mammals, played an antagonistic role to IRF1 in the activation of grass carp CIITA. These data suggested that grass carp, compared with mammals, has both conservative and unique mechanisms in the regulation of MHC II expression.

Biological Consequences of MHC-II Expression by Tumor Cells in Cancer

Immunotherapy has emerged as a key pillar of cancer treatment. To build upon the recent successes of immunotherapy, intense research efforts are aimed at a molecular understanding of antitumor immune responses, identification of biomarkers of immunotherapy response and resistance, and novel strategies to circumvent resistance. These studies are revealing new insight into the intricacies of tumor cell recognition by the immune system, in large part through MHCs. Although tumor cells widely express MHC-I, a subset of tumors originating from a variety of tissues also express MHC-II, an antigen-presenting complex traditionally associated with professional antigen-presenting cells. MHC-II is critical for antigen presentation to CD4+ T lymphocytes, whose role in antitumor immunity is becoming increasingly appreciated. Accumulating evidence demonstrates that tumor-specific MHC-II associates with favorable outcomes in patients with cancer, including those treated with immunotherapies, and with tumor rejection in murine models. Herein, we will review current research regarding tumor-enriched MHC-II expression and regulation in a range of human tumors and murine models, and the possible therapeutic applications of tumor-specific MHC-II.

Protective effects of CX3CR1 on autoimmune inflammation in a chronic EAE model for MS through modulation of antigen-presenting cell-related molecular MHC-II and its regulators

BACKGROUND

Recent evidences have implicated neuroprotective effects of CX3CR1 in multiple sclerosis (MS). But whether CX3CR1 is involved in modulation of antigen-presenting cell (APC)-related molecular MHC-II and what the possible mechanism is remain unidentified.

OBJECTIVE

In this study, we intended to investigate the effects of CX3CR1 on MHC-II expressions on brain myeloid cells in experimental autoimmune encephalomyelitis (EAE) mice and explore the possible regulators for it.

METHODS

CX3CR1-deficient EAE mice were created. Disease severity, pathological damage, and the expressions of MHC-II and its mediators on myeloid cells were detected.

RESULTS

We found that compare with wile-typed EAE mice, CX3CR1-deficient EAE mice exhibited more severe disease severity. An accumulation of CD45⁺CD115⁺Ly6C^-CD11c⁺ cells was reserved in the affected EAE brain of CX3CR1-deficient mice, consistent with disease severity and pathological damage in the brain. The expressions of MHC-II on the brain CD45⁺CD115⁺Ly6C^-CD11c⁺ cells of CX3CR1-deficient EAE mice were elevated, in accord with the increased protein and mRNA expressions of class II transactivator (CIITA) and interferon regulatory factor-1 (IRF-1).

CONCLUSIONS

The findings indicated that CX3CR1 might be an important regulator for MHC-II expressions on APCs, playing a beneficial role in EAE. The mechanism was probably through regulation on the MHC-II regulators CIITA and IRF-1.

Gene Expression Profiling of Lacrimal Glands Identifies the Ectopic Expression of MHC II on Glandular Cells as a Presymptomatic Feature in a Mouse Model of Primary Sjögren's Syndrome

Ectopic expression of MHC II molecules on glandular cells is a feature of primary Sjögren's syndrome (pSS). However, the cause of this ectopic expression and its potential role in the pathogenesis of the disease remains elusive. Here, we report that ectopic expression of MHC II molecules on glandular cells represents an early presymptomatic event in a mouse model of pSS induced by immunization of Ro60_316-335 peptide emulsified in TiterMax® as an adjuvant. Ectopic expression of MHC II was induced by TiterMax® but not by complete freund's adjuvant (CFA). Furthermore, immunization with Ro60_316-335 peptide emulsified in TiterMax®, but not in CFA, induced a pSS-like disease in mice. Our results suggests that ectopic expression of MHC II molecules on glandular cells represents a presymptomatic feature of pSS and that such ectopic expression can be induced by exogenous factors. In addition, this study also provides a novel mechanism how adjuvants can amplify immune responses.

Positive selection in coding regions and motif duplication in regulatory regions of bottlenose dolphin MHC class II genes

The vertebrate immune response is mediated through highly adaptive, quickly evolving cell surface receptors, the major histocompatibility complex (MHC). MHC molecules bind and present a diverse array of pathogenic molecules and trigger a cascade of defenses. Use of MHC variation as a marker for population health has also evolved quickly following advances in sequencing methods. We applied a combination of traditional and next generation sequencing methodology to characterize coding (peptide binding region) and regulatory (proximal promoter) sequence variation in MHC Class II DQA and DQB genes between estuarine and coastal populations of the bottlenose dolphin, Tursiops truncatus, an apex predator whose health status is indicative of anthropogenic impacts on the ecosystem. The coding regions had 10 alleles each at DQA and DQB; the promoters had 6 and 7 alleles at DQA and DQB, respectively with variation within key regulatory motifs. Positive selection was observed for the coding regions of both genes while both coding and promoter regions exhibited geographic differences in allele composition that likely indicates diversifying selection across habitats. Most notable was the discovery of a complete duplication of a 14-bp T-box motif in the DQA promoter. Four class II promoter regions (DQA, DQB, DRA, DRB) were characterized in species from four cetacean families (Delphinidae, Monodontidae, Lipotidae, and Physeteridae) and revealed substantial promoter structural diversity across this order. Peptide binding regions may not be the only source of adaptive potential within cetacean MHC for responding to pathogenic threats. These findings are the first analysis of cetacean MHC regulatory motifs, which may divulge unique immunogenetic strategies among cetaceans and reveal how MHC transcriptional control continues to evolve. The combined MHC regulatory and coding data provide new genetic context for distinct vulnerability profiles between coastal and estuarine populations, which are key concerns for health and risk management.

Expression of HLA-DQA1 and HLA-DQB1 genes in B lymphocytes, monocytes and whole blood

Differential expression of HLA-DQA1 and HLA-DQB1 gene alleles was analysed in three different cell populations isolated from peripheral blood-B lymphocytes, monocytes and whole-blood cells. Interallelic differences in mRNA levels were observed: DQA1*03 alleles were among the most expressed in all cell types, whereas DQA1*05 alleles were least expressed in whole blood and monocytes and among the most expressed in B cells. For DQB1 gene, DQB1*06 group of alleles were the most expressed, and DQB1*02 group the least expressed within all cell populations examined. In comparison with the rest alleles, DQB1*06 and DQB1*05:02 alleles have higher expression in monocytes than in B cells, professional antigen-presenting cells. Cell type-specific regulation of expression was observed as well, with higher and more balanced expression of alleles in B lymphocytes compared to monocytes.

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.

STAT3 and NF-κB are Simultaneously Suppressed in Dendritic Cells in Lung Cancer

Tumour-induced dendritic cell (DC) dysfunction plays an important role in cancer immune escape. However, the underlying mechanisms are not yet fully understood, reflecting the lack of appropriate experimental models both in vivo and in vitro. In the present study, an in vitro study model for tumour-induced DC dysfunction was established by culturing DCs with pooled sera from multiple non-small cell lung cancer (NSCLC) patients. The results demonstrated that tumour-induced human monocyte-derived DCs exhibited systematic functional deficiencies. Transcriptomics analysis revealed that the expression of major functional cluster genes, including the MHC class II family, cytokines, chemokines, and co-stimulatory molecules, was significantly altered in tumour-induced DCs compared to that in control cells. Further examination confirmed that both NF-κB and STAT3 signalling pathways were simultaneously repressed by cancer sera, suggesting that the attenuated NF-κB and STAT3 signalling could be the leading cause of DC dysfunction in cancer. Furthermore, reversing the deactivated NF-κB and STAT3 signalling could be a strategy for cancer immunotherapy.

Presence of HLA-DR Molecules and HLA-DRB1 mRNA in Circulating CD4(+) T Cells

The human major histocompatibility complex class II isotype HLA-DR is currently used as an activation marker for T cells. However, whether an endogenous protein expression or a molecular acquisition accounts for the presence of HLA-DR on T cells remains undetermined and still controversial. To further characterize this phenomenon, we compared several aspects of the presence of the HLA-DR protein to the presence of associated mRNA (HLA-DRB1), focusing on human T cells from peripheral blood of healthy individuals. Using a flow cytometric approach, we determined that the HLA-DR observed on CD4(+) T cells was almost exclusively cell surface-associated, while for autologous CD19(+) B cells, the protein could be located in the plasma membrane as well as in the cytoplasm. Moreover, negligible expression levels of HLA-DRB1 were found in CD4(+) T cells, using an HLA-DRB1 allele-specific qPCR assay. Finally, the presence of HLA-DR was not confined to activated CD4(+) and CD8(+) T cells, as evaluated by the co-expression of CD25. The functional role of the HLA-DR molecule on T cells remains enigmatic; however, this study presents evidence of fundamental differences for the presence of HLA-DR on T cells from HLA-DR in the context of antigen-presenting cells, which is a well-known phenomenon. Although an inducible endogenous protein expression cannot be excluded for the T cells, our findings suggest that a re-evaluation of the HLA-DR as a T cells activation marker is warranted.

NF-Y and the immune response: Dissecting the complex regulation of MHC genes

Nuclear Factor Y (NF-Y) was first described as one of the CCAAT binding factors. Although CCAAT motifs were found to be present in various genes, NF-Y attracted a lot of interest early on, due to its role in Major Histocompatibility Complex (MHC) gene regulation. MHC genes are crucial in immune response and show peculiar expression patterns. Among other conserved elements on MHC promoters, an NF-Y binding CCAAT box was found to contribute to MHC transcriptional regulation. NF-Y along with other DNA binding factors assembles in a stereospecific manner to form a multiprotein scaffold, the MHC enhanceosome, which is necessary but not sufficient to drive transcription. Transcriptional activation is achieved by the recruitment of yet another factor, the class II transcriptional activator (CIITA). In this review, we briefly discuss basic findings on MHCII transcription regulation and we highlight NF-Y different modes of function in MHCII gene activation. This article is part of a Special Issue entitled: Nuclear Factor Y in Development and Disease, edited by Prof. Roberto Mantovani.

Immune responses against protozoan parasites: a focus on the emerging role of Nod-like receptors

Nod-like receptors (NLRs) have gained attention in recent years because of the ability of some family members to assemble into a multimeric protein complex known as the inflammasome. The role of NLRs and the inflammasome in regulating innate immunity against bacterial pathogens has been well studied. However, recent studies show that NLRs and inflammasomes also play a role during infections caused by protozoan parasites, which pose a significant global health burden. Herein, we review the diseases caused by the most common protozoan parasites in the world and discuss the roles of NLRs and inflammasomes in host immunity against these parasites.

Role of antigen presentation in the production of pro-inflammatory cytokines in obese adipose tissue

Type II diabetes regroups different physiological anomalies that ultimately lead to low-grade chronic inflammation, insulin resistance and loss of pancreatic β-cells. Obesity is one of the best examples of such a condition that can develop into Metabolic Syndrome, causing serious health problems of great socio-economic consequences. The pathological outcome of obesity has a genetic basis and depends on the delicate balance between pro- and anti-inflammatory effectors of the immune system. The causal link between obesity and inflammation is well established. While innate immunity plays a key role in the development of a pro-inflammatory state in obese adipose tissues, it has now become clear that adaptive immune cells are also involved and participate in the cascade of events that lead to metabolic perturbations. The efficacy of some immunotherapeutic protocols in reducing the symptoms of obesity-driven metabolic syndrome in mice implicated all arms of the immune response. Recently, the production of pathogenic immunoglobulins and pro-inflammatory cytokines by B and T lymphocytes suggested an auto-immune basis for the establishment of a non-healthy obese state. Understanding the cellular landscape of obese adipose tissues and how immune cells sustain chronic inflammation holds the key to the development of targeted therapies. In this review, we emphasize the role of antigen-presenting cells and MHC molecules in obese adipose tissue and the general contribution of the adaptive arm of the immune system in inflammation-induced insulin resistance.

NLRs: Nucleotide-Binding Domain and Leucine-Rich-Repeat-Containing Proteins

Eukaryotes have evolved strategies to detect microbial intrusion and instruct immune responses to limit damage from infection. Recognition of microbes and cellular damage relies on the detection of microbe-associated molecular patterns (MAMPs, also called PAMPS, or pathogen-associated molecular patterns) and so-called "danger signals" by various families of host pattern recognition receptors (PRRs). Members of the recently identified protein family of nucleotide-binding domain andleucine-rich-repeat-containing proteins (NLR), including Nod1, Nod2, NLRP3, and NLRC4, have been shown to detect specific microbial motifs and danger signals for regulating host inflammatory responses. Moreover, with the discovery that polymorphisms in NOD1, NOD2, NLRP1, and NLRP3 are associated with susceptibility to chronic inflammatory disorders, the view has emerged that NLRs act not only as sensors butalso can serve as signaling platforms for instructing and balancing host immune responses. In this chapter, we explore the functions of these intracellular innate immune receptors and examine their implication in inflammatory diseases.

Identification of a nuclear export sequence in the MHC CIITA

Initiation of an immune response through expression of MHC class II and related genes is under the control of the CIITA. Normally found in both the cytoplasm and nucleus, CIITA is tightly controlled by a variety of posttranslational modifications as well as interactions with other nuclear and cytoplasmic factors, whereas disruption of this dual subcellular localization impairs CIITA functioning and expression of target genes. Although CIITA has well-defined domains necessary for its nuclear import, the region responsible for the translocation of CIITA from the nucleus has not been characterized. In this study, we identify a leucine-rich motif at residues 717-724 that bears strong homology to known nuclear export sequence (NES) domains. Mutation of this region renders CIITA insensitive to treatment with leptomycin B, an inhibitor of nuclear export, whereas fusion of this domain to a heterologous GFP is sufficient to induce its export to the cytoplasm or cause its retention in the nucleus following leptomycin B treatment. Point mutations of specific leucine residues within the NES disrupt the normal subcellular distribution of the full-length CIITA, impair its ability to interact with the nuclear export factor CRM1, and enhance CIITA-induced gene expression from an MHC class II gene promoter. IFN-γ stimulation of class II genes is further enhanced by inhibiting the nuclear export of endogenous CIITA. Collectively, these data demonstrate the first identification of a specific NES within CIITA and place it among the other protein domains that contribute to the posttranslational regulation of CIITA activity.

Clinical features of idiopathic inflammatory polymyopathy in the Hungarian Vizsla

BACKGROUND

A retrospective study of the clinicopathological features of presumed and confirmed cases of idiopathic inflammatory polymyopathy in the Hungarian Vizsla dog and guidelines for breeding.

RESULTS

369 medical records were reviewed (1992-2013) and 77 Hungarian Vizslas were identified with a case history consistent with idiopathic inflammatory polymyopathy. Inclusion criteria were: group 1 (confirmed diagnosis); histopathology and clinical findings compatible with an inflammatory polymyopathy and group 2 (probable diagnosis); clinical findings compatible with a polymyopathy including dysphagia, sialorrhea, temporal muscle atrophy, elevated serum creatine kinase (CK) activity, and sufficient clinical history to suggest that other neuromuscular disorders could be ruled out. Some group 2 dogs had muscle biopsy, which suggested muscle disease but did not reveal an inflammatory process. The mean age of onset was 2.4 years; male dogs were slightly overrepresented. Common presenting signs were dysphagia, sialorrhea, masticatory muscle atrophy, and regurgitation. Common muscle histopathological findings included degenerative and regenerative changes, with multifocal mononuclear cell infiltration with lymphoplasmacytic myositis of variable severity. A positive response to immunosuppressive treatment supported an immune-mediated aetiology. The mean age at death and survival time were 6.4 and 3.9 years, respectively. Recurrence of clinical signs and aspiration pneumonia were common reasons for euthanasia.

CONCLUSIONS

Diagnosis of Vizsla idiopathic inflammatory polymyopathy can be challenging due to lack of specific tests, however the presence of dysphagia, regurgitation and masticatory muscle atrophy in this breed with negative serological tests for masticatory muscle myositis and myasthenia gravis, along with muscle biopsies suggesting an inflammatory process, support the diagnosis. However, there is an urgent need for a more specific diagnostic test. The average of inbreeding coefficient (CoI) of 16.3% suggests an increased expression of a Dog Leukocyte Antigen Class II haplotype, leading to an increased disease risk. The prognosis remains guarded, as treatment can only manage the disease. Recurrence of clinical signs and perceived poor quality of life are the most common reasons for humane euthanasia.

Kaposi's Sarcoma-Associated Herpesvirus Latency-Associated Nuclear Antigen Inhibits Major Histocompatibility Complex Class II Expression by Disrupting Enhanceosome Assembly through Binding with the Regulatory Factor X Complex

Major histocompatibility complex class II (MHC-II) molecules play a central role in adaptive antiviral immunity by presenting viral peptides to CD4(+) T cells. Due to their key role in adaptive immunity, many viruses, including Kaposi's sarcoma-associated herpesvirus (KSHV), have evolved multiple strategies to inhibit the MHC-II antigen presentation pathway. The expression of MHC-II, which is controlled mainly at the level of transcription, is strictly dependent upon the binding of the class II transactivator (CIITA) to the highly conserved promoters of all MHC-II genes. The recruitment of CIITA to MHC-II promoters requires its direct interactions with a preassembled MHC-II enhanceosome consisting of cyclic AMP response element-binding protein (CREB) and nuclear factor Y (NF-Y) complex and regulatory factor X (RFX) complex proteins. Here, we show that KSHV-encoded latency-associated nuclear antigen (LANA) disrupts the association of CIITA with the MHC-II enhanceosome by binding to the components of the RFX complex. Our data show that LANA is capable of binding to all three components of the RFX complex, RFX-associated protein (RFXAP), RFX5, and RFX-associated ankyrin-containing protein (RFXANK), in vivo but binds more strongly with the RFXAP component in in vitro binding assays. Levels of MHC-II proteins were significantly reduced in KSHV-infected as well as LANA-expressing B cells. Additionally, the expression of LANA in a luciferase promoter reporter assay showed reduced HLA-DRA promoter activity in a dose-dependent manner. Chromatin immunoprecipitation assays showed that LANA binds to the MHC-II promoter along with RFX proteins and that the overexpression of LANA disrupts the association of CIITA with the MHC-II promoter. These assays led to the conclusion that the interaction of LANA with RFX proteins interferes with the recruitment of CIITA to MHC-II promoters, resulting in an inhibition of MHC-II gene expression. Thus, the data presented here identify a novel mechanism used by KSHV to downregulate the expressions of MHC-II genes.

IMPORTANCE

Kaposi's sarcoma-associated herpesvirus is the causative agent of multiple human malignancies. It establishes a lifelong latent infection and persists in infected cells without being detected by the host's immune surveillance system. Only a limited number of viral proteins are expressed during latency, and these proteins play a significant role in suppressing both the innate and adaptive immunities of the host. Latency-associated nuclear antigen (LANA) is one of the major proteins expressed during latent infection. Here, we show that LANA blocks MHC-II gene expression to subvert the host immune system by disrupting the MHC-II enhanceosome through binding with RFX transcription factors. Therefore, this study identifies a novel mechanism utilized by KSHV LANA to deregulate MHC-II gene expression, which is critical for CD4(+) T cell responses in order to escape host immune surveillance.

Intracellular delivery of CII TA genes by polycationic liposomes for suppressed immune response of dendritic cells

Construction of an effective nanocomplex for suppression of CII TA proteins can be a potential strategy for inhibiting unwanted immune response.

Molecular characterization of chicken class II transactivator gene

Class II transactivator (CIITA) is an effective transcriptional factor regulating various genes in the immune system. Since the detection of CIITA in 1993, there has been considerable progress toward understanding its role as an activator of MHC II genes in human and mouse; however, there is little knowledge of this gene in other animals such as chicken. Molecular characterization of the chicken CIITA gene transcript was performed to determine its sequence and expression in different tissues. The CIITA cDNA was first generated through reverse transcriptase-polymerase chain reaction (RT-PCR) from Cobb chicken spleen cell RNA, using oligonucleotide primers based on the predicted cDNA sequence. The effect of the immune system stimulation on the CIITA gene expression in kidney, liver, thymus, and spleen were assessed by semi-quantitative RT-PCR analysis. A partial cDNA sequence (1,688 bp) encoding part of the NACHT domain followed by seven of the transactivator and one of the NLS domains were obtained. Comparison of the deduced amino acid sequence with other CIITAs reveals high level of similarities in amino acid composition, secondary structure and phosphorylation sites. Furthermore, in comparison to the Red Jungle Fowl (RJF) sequence, we found 17 single nucleotide polymorphisms in Cobb broiler chicken, ten of which were reported for the first time. Gene expression analysis indicated that CIITA RNA amounts increased in all the examined tissues following stimulation with Brucella antigen. This investigation may indicate that CIITA molecule has an important role in the chicken immune responses as well as human and other animals.

Boosting the MHC Class II-Restricted Tumor Antigen Presentation to CD4+ T Helper Cells: A Critical Issue for Triggering Protective Immunity and Re-Orienting the Tumor Microenvironment Toward an Anti-Tumor State

Although the existence of an immune response against tumor cells is well documented, the fact that tumors take off in cancer patients indicates that neoplastic cells can circumvent this response. Over the years many investigators have described strategies to rescue the anti-tumor immune response with the aim of creating specific and long-lasting protection against the disease. When exported to human clinical settings, these strategies have revealed in most cases a very limited, if any, positive outcome. We believe that the failure is mostly due to the inadequate triggering of the CD4+ T helper (TH) cell arm of the adaptive immunity, as TH cells are necessary to trigger all the immune effector mechanisms required to eliminate tumor cells. In this review, we focus on novel strategies that by stimulating MHC class II-restricted activation of TH cells generate a specific and persistent adaptive immunity against the tumor. This point is of critical importance for both preventive and therapeutic anti-tumor vaccination protocols, because adaptive immunity with its capacity to produce specific, long-lasting protection and memory responses is indeed the final goal of vaccination. We will discuss data from our as well as other laboratories which strongly suggest that triggering a specific and persistent anti-tumor CD4+ TH cell response stably modify not only the tumor microenvironment but also tumor-dependent extratumor microenvironments by eliminating and/or reducing the blood-derived tumor infiltrating cells that may have a pro-tumor growth function such as regulatory CD4+/CD25+ T cells and myeloid-derived-suppressor cells. Within this frame, therefore, we believe that the establishment of a pro-tumor environment is not the cause but simply the consequence of the tumor strategy to primarily counteract components of the adaptive cellular immunity, particularly TH lymphocytes.

CIITA and Its Dual Roles in MHC Gene Transcription

Class II transactivator (CIITA) is a transcriptional coactivator that regulates γ-interferon-activated transcription of Major Histocompatibility Complex (MHC) class I and II genes. As such, it plays a critical role in immune responses: CIITA deficiency results in aberrant MHC gene expression and consequently in autoimmune diseases such as Type II bare lymphocyte syndrome. Although CIITA does not bind DNA directly, it regulates MHC transcription in two distinct ways - as a transcriptional activator and as a general transcription factor. As an activator, CIITA nucleates an enhanceosome consisting of the DNA binding transcription factors RFX, cyclic AMP response element binding protein, and NF-Y. As a general transcription factor, CIITA functionally replaces the TFIID component, TAF1. Like TAF1, CIITA possesses acetyltransferase (AT) and kinase activities, both of which contribute to proper transcription of MHC class I and II genes. The substrate specificity and regulation of the CIITA AT and kinase activities also parallel those of TAF1. In addition, CIITA is tightly regulated by its various regulatory domains that undergo phosphorylation and influence its targeted localization. Thus, a complex picture of the mechanisms regulating CIITA function is emerging suggesting that CIITA has dual roles in transcriptional regulation which are summarized in this review.

Alarmins, inflammasomes and immunity

The elaboration of an effective immune response against pathogenic microbes such as viruses, intracellular bacteria or protozoan parasites relies on the recognition of microbial products called pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs) such as Toll-like receptors (TLRs). Ligation of the PRRs leads to synthesis and secretion of pro-inflammatory cytokines and chemokines. Infected cells and other stressed cells also release host-cell derived molecules, called damage-associated molecular patterns (DAMPs, danger signals, or alarmins), which are generic markers for damage. DAMPs are recognized by specific receptors on both immune and nonimmune cells, which, depending on the target cell and the cellular context, can lead to cell differentiation or cell death, and either inflammation or inhibition of inflammation. Recent research has revealed that DAMPs and PAMPs synergize to permit secretion of pro-inflammatory cytokines such as interleukin-1β (IL-1β): PAMPs stimulate synthesis of pro-IL-1β, but not its secretion; while DAMPs can stimulate assembly of an inflammasome containing, usually, a Nod-like receptor (NLR) member, and activation of the protease caspase-1, which cleaves pro-IL-1β into IL-1β, allowing its secretion. Other NLR members do not participate in formation of inflammasomes but play other essential roles in regulation of the innate immune response.

Synthetic DNA vaccines: improved vaccine potency by electroporation and co-delivered genetic adjuvants

In recent years, DNA vaccines have undergone a number of technological advancements that have incited renewed interest and heightened promise in the field. Two such improvements are the use of genetically engineered cytokine adjuvants and plasmid delivery via in vivo electroporation (EP), the latter of which has been shown to increase antigen delivery by nearly 1000-fold compared to naked DNA plasmid delivery alone. Both strategies, either separately or in combination, have been shown to augment cellular and humoral immune responses in not only mice, but also in large animal models. These promising results, coupled with recent clinical trials that have shown enhanced immune responses in humans, highlight the bright prospects for DNA vaccines to address many human diseases.

Histone deacetylase inhibitors activate CIITA and MHC class II antigen expression in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL), the most common form of non-Hodgkin's lymphoma (NHL) diagnosed in the USA, consists of at least two distinct subtypes: germinal centre B (GCB) and activated B-cell (ABC). Decreased MHC class II (MHCII) expression on the tumours in both DLBCL subtypes directly correlates with significant decreases in patient survival. One common mechanism accounting for MHCII down-regulation in DLBCL is reduced expression of the MHC class II transactivator (CIITA), the master regulator of MHCII transcription. Furthermore, reduced CIITA expression in ABC DLBCL correlates with the presence of the transcriptional repressor positive regulatory domain-I-binding factor-1 (PRDI-BF1). However, the mechanisms underlying down-regulation of CIITA in GCB DLBCL are currently unclear. In this study, we demonstrate that neither PRDI-BF1 nor CpG hypermethylation at the CIITA promoters are responsible for decreased CIITA in GCB DLBCL. In contrast, histone modifications associated with an open chromatin conformation and active transcription were significantly lower at the CIITA promoters in CIITA(-) GCB cells compared with CIITA(+) B cells, which suggests that epigenetic mechanisms contribute to repression of CIITA transcription. Treatment of CIITA(-) or CIITA(low) GCB cells with several different histone deacetylase inhibitors (HDACi) activated modest CIITA and MHCII expression. However, CIITA and MHCII levels were significantly higher in these cells after exposure to the HDAC-1-specific inhibitor MS-275. These results suggest that CIITA transcription is repressed in GCB DLBCL cells through epigenetic mechanisms involving HDACs, and that HDACi treatment can alleviate repression. These observations may have important implications for patient therapy.

IK induced by coxsackievirus B3 infection transiently downregulates expression of MHC class II through increasing cAMP

Major histocompatibility complex (MHC) class II expression is critical for the presentation of antigens in the immune response to viral infection. Consequently, some viruses regulate the MHC class II-mediated presentation of viral antigens as a mechanism of immune escape. In this study, we found that Coxsackievirus B3 (CVB3) infection transiently increased IK expression, which reduced the expression of MHC class II (I-A/I-E) on splenic B cells. Interestingly, CVB3-induced IK elevated cAMP, a downstream molecule of the G protein-coupled receptors, which inhibited MHC class II presentation on B cells. Transgenic mice expressing truncated IK showed lower expression of MHC class II on B cells than did wild-type mice after CVB3 infection. Taken together, these results imply that IK plays a role in downregulating MHC class II expression on B cells during CVB3 infection through the induction of cAMP.