Intracellular transport of class II MHC molecules directed by invariant chain

Hydroxychloroquine in obstetrics: potential implications of the prophylactic use of hydroxychloroquine for placental insufficiency during pregnancy

Proper placentation during early pregnancy is a key factor for maintaining a healthy pregnancy. Placental insufficiency leads to critical complications such as preeclampsia, fetal growth restriction, and fetal demise. These complications are often associated with pathological findings of restricted remodeling and obstructive lesions of the myometrial spiral arteries, which have high recurrence rates during subsequent pregnancies. Currently, there are no pharmacological interventions other than aspirin for the prevention of preeclampsia. Hydroxychloroquine (HCQ), a well-known antimalarial drug, reduces inflammatory and thrombotic changes in vessels. For decades, the use of HCQ for autoimmune diseases has resulted in the successful prevention of both arterial and venous thrombotic events and has been extended to the treatment of lupus and antiphospholipid antibody syndrome during pregnancy. HCQ reduces the risk of preeclampsia with lupus by up to 90%. Several recent studies have investigated whether HCQ improves pregnancy outcomes in women with a history of poor outcomes. In addition, in vitro and animal studies have demonstrated the beneficial effects of HCQ in improving endothelial dysfunction and alleviating hypertension and proteinuria. Therefore, we hypothesized that HCQ has the potential to attenuate the vascular inflammatory and thrombogenic pathways associated with placental insufficiency and conducted a multicenter clinical trial on the efficacy of combining aspirin with HCQ for pregnancies at high risk for preeclampsia in Korea. This study summarizes the potential effects of HCQ on pregnancies with placental insufficiency and the implications of HCQ treatment in the field of obstetrics.

Non-biologic immunosuppressive drugs for inflammatory and autoimmune skin diseases

Non-biologic immunosuppressive drugs, such as azathioprine, dapsone or methotrexate are fundamental treatment options for a wide range of autoimmune and chronic inflammatory skin diseases. Some of these drugs were initially used for malignancies (e.g., azathioprine or methotrexate) or infectious diseases (e.g., hydroxychloroquine or dapsone) but are nowadays mostly used for their immunosuppressive/immunomodulating action. Although dermatologists have years of clinical experience with these drugs, some of the mechanisms of action are not fully understood and are the subject of research. Although these drugs are commonly used, lack of experience or knowledge regarding their safety profiles and management leads to skepticism among physicians. Here, we summarize the mechanism of action and detailed management of adverse effects of the most commonly used immunosuppressive drugs for skin diseases. Furthermore, we discuss the management of these drugs during pregnancy and breastfeeding, as well as their interaction and handling during vaccination.

Nicht-Biologika-Immunsuppressiva bei entzündlichen und autoimmunen Hautkrankheiten: Non-biologic immunosuppressive drugs for inflammatory and autoimmune skin diseases

Nicht‐Biologika‐Immunsuppressiva wie Azathioprin, Dapson oder Methotrexat sind grundlegende Behandlungsmöglichkeiten für ein breites Spektrum von Autoimmunerkrankungen und chronisch‐entzündlichen Hauterkrankungen. Einige dieser Medikamente wurden ursprünglich bei malignen Erkrankungen (zum Beispiel Azathioprin oder Methotrexat) oder Infektionskrankheiten (zum Beispiel Hydroxychloroquin oder Dapson) eingesetzt, werden aber heute hauptsächlich wegen ihrer immunsuppressiven/immunmodulierenden Wirkung verwendet. Obwohl Dermatologen über jahrelange klinische Erfahrung mit diesen Arzneimitteln verfügen, sind einige der Wirkmechanismen noch nicht vollständig geklärt und noch Gegenstand der Forschung. Obwohl diese Medikamente häufig eingesetzt werden, führen mangelnde Erfahrung oder fehlendes Wissen über ihre Sicherheitsprofile und ihr Management zu einer skeptischen Haltung bei den Ärzten. Hier fassen wir den Wirkmechanismus und das detaillierte Management der Nebenwirkungen der am häufigsten verwendeten immunsuppressiven Medikamente für Hautkrankheiten zusammen. Darüber hinaus diskutieren wir den Umgang mit diesen Medikamenten während der Schwangerschaft und Stillzeit sowie ihre Wechselwirkung und Handhabung im Zusammenhang mit Impfungen.

Serum biomarkers and their relationship to axial spondyloarthritis associated with inflammatory bowel diseases

Spondyloarthritis (SpA) constitute a group of chronic inflammatory immune-mediated rheumatic diseases characterized by genetic, clinical, and radiological features. Recent efforts have concentrated on identifying biomarkers linked to axial SpA associated with inflammatory bowel disease (IBD), offering predictive insights into disease onset, activity, and progression. Genetically, the significance of the HLA-B27 antigen is notably diminished in ankylosing spondylitis (AS) associated with IBD, but is heightened in concurrent sacroiliitis. Similarly, certain polymorphisms of endoplasmic reticulum aminopeptidase (ERAP-1) appear to be involved. Carriage of variant NOD2/CARD15 polymorphisms has been demonstrated to correlate with the risk of subclinical intestinal inflammation in AS. Biomarkers indicative of pro-inflammatory activity, including C-reactive protein (CRP) along with erythrocyte sedimentation rate (ESR), are among the consistent predictive biomarkers of disease progression. Nevertheless, these markers are not without limitations and exhibit relatively low sensitivity. Other promising markers encompass IL-6, serum calprotectin (s-CLP), serum amyloid (SAA), as well as biomarkers regulating bone formation such as metalloproteinase-3 (MMP-3) and Dickkopf-related protein 1 (DKK-1). Additional candidate indicators of structural changes in SpA patients include matrix metalloproteinase-3 (MMP-3), vascular endothelial growth factor (VEGF), tenascin C (TNC), and CD74 IgG. Fecal caprotein (f-CLP) levels over long-term follow-up of AS patients have demonstrated predictive value in anticipating the development of IBD. Serologic antibodies characteristic of IBD (ASCA, ANCA) have also been compared; however, results exhibit variability. In this review, we will focus on biomarkers associated with both axial SpA and idiopathic intestinal inflammation, notably enteropathic spondyloarthritis.

The role of the antigen processing machinery in the regulation and trafficking of intracellular -Toll-like receptor molecules

Intracellular Toll-like receptors (TLRs) are key components of the innate immune system. Their expression in antigen-presenting cells (APCs), and in particular dendritic cells (DCs), makes them critical in the induction of the adaptive immune response. In DCs, they interact with the chaperone UNC93B1 that mediates their trafficking from the endoplasmic reticulum (ER) to endosomes where they are cleaved by proteases and activated. All these different steps are also shared by major histocompatibility complex class-II (MHCII) molecules. Here, we will discuss the tight relationship intracellular TLRs have with the antigen processing machinery in APCs for their trafficking and activation.

Immunosuppression by hydroxychloroquine: mechanistic proof in in vitro experiments but limited systemic activity in a randomized placebo-controlled clinical pharmacology study

Based on its wide range of immunosuppressive properties, hydroxychloroquine (HCQ) is used for the treatment of several autoimmune diseases. Limited literature is available on the relationship between HCQ concentration and its immunosuppressive effect. To gain insight in this relationship, we performed in vitro experiments in human PBMCs and explored the effect of HCQ on T and B cell proliferation and Toll-like receptor (TLR)3/TLR7/TLR9/RIG-I-induced cytokine production. In a placebo-controlled clinical study, these same endpoints were evaluated in healthy volunteers that were treated with a cumulative dose of 2400 mg HCQ over 5 days. In vitro, HCQ inhibited TLR responses with IC50s > 100 ng/mL and reaching 100% inhibition. In the clinical study, maximal HCQ plasma concentrations ranged from 75 to 200 ng/mL. No ex vivo HCQ effects were found on RIG-I-mediated cytokine release, but there was significant suppression of TLR7 responses and mild suppression of TLR3 and TLR9 responses. Moreover, HCQ treatment did not affect B cell and T cell proliferation. These investigations show that HCQ has clear immunosuppressive effects on human PBMCs, but the effective concentrations exceed the circulating HCQ concentrations under conventional clinical use. Of note, based on HCQ's physicochemical properties, tissue drug concentrations may be higher, potentially resulting in significant local immunosuppression. This trial is registered in the International Clinical Trials Registry Platform (ICTRP) under study number NL8726.

Membrane protein trafficking in the anti-tumor immune response: work of endosomal-lysosomal system

Immunotherapy has changed the treatment landscape for multiple cancer types. In the recent decade, great progress has been made in immunotherapy, including immune checkpoint inhibitors, adoptive T-cell therapy, and cancer vaccines. ICIs work by reversing tumor-induced immunosuppression, resulting in robust activation of the immune system and lasting immune responses. Whereas, their clinical use faces several challenges, especially the low response rate in most patients. As an increasing number of studies have focused on membrane immune checkpoint protein trafficking and degradation, which interferes with response to immunotherapy, it is necessary to summarize the mechanism regulating those transmembrane domain proteins translocated into the cytoplasm and degraded via lysosome. In addition, other immune-related transmembrane domain proteins such as T-cell receptor and major histocompatibility are associated with neoantigen presentation. The endosomal-lysosomal system can also regulate TCR and neoantigen-MHC complexes on the membrane to affect the efficacy of adoptive T-cell therapy and cancer vaccines. In conclusion, we discuss the process of surface delivery, internalization, recycling, and degradation of immune checkpoint proteins, TCR, and neoantigen-MHC complexes on the endosomal-lysosomal system in biology for optimizing cancer immunotherapy.

The Autophagy Receptor TAX1BP1 (T6BP) improves antigen presentation by MHC-II molecules

CD4⁺ T lymphocytes play a major role in the establishment and maintenance of immunity. They are activated by antigenic peptides derived from extracellular or newly synthesized (endogenous) proteins presented by the MHC-II molecules. The pathways leading to endogenous MHC-II presentation remain poorly characterized. We demonstrate here that the autophagy receptor, T6BP, influences both autophagy-dependent and -independent endogenous presentation of HIV- and HCMV-derived peptides. By studying the immunopeptidome of MHC-II molecules, we show that T6BP affects both the quantity and quality of peptides presented. T6BP silencing induces the mislocalization of the MHC-II-loading compartments and rapid degradation of the invariant chain (CD74) without altering the expression and internalization kinetics of MHC-II molecules. Defining the interactome of T6BP, we identify calnexin as a T6BP partner. We show that the calnexin cytosolic tail is required for this interaction. Remarkably, calnexin silencing replicates the functional consequences of T6BP silencing: decreased CD4⁺ T cell activation and exacerbated CD74 degradation. Altogether, we unravel T6BP as a key player of the MHC-II-restricted endogenous presentation pathway, and we propose one potential mechanism of action.

Diabetes-Modifying Antirheumatic Drugs: The Roles of DMARDs as Glucose-Lowering Agents

Systemic inflammation represents a shared pathophysiological mechanism which underlies the frequent clinical associations among chronic inflammatory rheumatic diseases (CIRDs), insulin resistance, type 2 diabetes (T2D), and chronic diabetes complications, including cardiovascular disease. Therefore, targeted anti-inflammatory therapies are attractive and highly desirable interventions to concomitantly reduce rheumatic disease activity and to improve glucose control in patients with CIRDs and comorbid T2D. Therapeutic approaches targeting inflammation may also play a role in the prevention of prediabetes and diabetes in patients with CIRDs, particularly in those with traditional risk factors and/or on high-dose corticosteroid therapy. Recently, several studies have shown that different disease-modifying antirheumatic drugs (DMARDs) used for the treatment of CIRDs exert antihyperglycemic properties by virtue of their anti-inflammatory, insulin-sensitizing, and/or insulinotropic effects. In this view, DMARDs are promising drug candidates that may potentially reduce rheumatic disease activity, ameliorate glucose control, and at the same time, prevent the development of diabetes-associated cardiovascular complications and metabolic dysfunctions. In light of their substantial antidiabetic actions, some DMARDs (such as hydroxychloroquine and anakinra) could be alternatively termed “diabetes-modifying antirheumatic drugs”, since they may be repurposed for co-treatment of rheumatic diseases and comorbid T2D. However, there is a need for future randomized controlled trials to confirm the beneficial metabolic and cardiovascular effects as well as the safety profile of distinct DMARDs in the long term. This narrative review aims to discuss the current knowledge about the mechanisms behind the antihyperglycemic properties exerted by a variety of DMARDs (including synthetic and biologic DMARDs) and the potential use of these agents as antidiabetic medications in clinical settings.

Effect of Anti-Rheumatic Drugs on Cardiovascular Disease Events in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by erosive arthritis, which can involve multiple systems. Patients with RA may have a variety of comorbidities, including cardiovascular disease (CVD), lung cancer, lymphoma, infection, osteoporosis, fatigue, depression, colon cancer, breast cancer, prostate cancer, and Alzheimer's disease. Among these comorbidities, the incidence of CVD, lung cancer, lymphoma, infection, and osteoporosis is higher. CVD is a serious complication of RA. The risk of CVD and associated mortality rate in patients with RA is high, and the treatment rate is low. In addition to traditional risk factors, such as age, sex, blood pressure, and diabetes, RA is also associated with inflammation. Furthermore, therapeutic drugs for RA, including non-steroidal anti-inflammatory drugs, glucocorticoids, and disease-modifying anti-rheumatic drugs, have beneficial or harmful effects on cardiovascular events in patients with RA. This article discusses the effects of therapeutic drugs for RA on cardiovascular events.

Lipid metabolism in autoimmune rheumatic disease: implications for modern and conventional therapies

Suppressing inflammation has been the primary focus of therapies in autoimmune rheumatic diseases (AIRDs), including rheumatoid arthritis and systemic lupus erythematosus. However, conventional therapies with low target specificity can have effects on cell metabolism that are less predictable. A key example is lipid metabolism; current therapies can improve or exacerbate dyslipidemia. Many conventional drugs also require in vivo metabolism for their conversion into therapeutically beneficial products; however, drug metabolism often involves the additional formation of toxic by-products, and rates of drug metabolism can be heterogeneous between patients. New therapeutic technologies and research have highlighted alternative metabolic pathways that can be more specifically targeted to reduce inflammation but also to prevent undesirable off-target metabolic consequences of conventional antiinflammatory therapies. This Review highlights the role of lipid metabolism in inflammation and in the mechanisms of action of AIRD therapeutics. Opportunities for cotherapies targeting lipid metabolism that could reduce immunometabolic complications and potential increased cardiovascular disease risk in patients with AIRDs are discussed.

B Cell Involvement in the Pathogenesis of Ankylosing Spondylitis

Extensive research into ankylosing spondylitis (AS) has suggested the major role of genetics, immune reactions, and the joint-gut axis in its etiology, although an ultimate consensus does not yet exist. The available evidence indicates that both autoinflammation and T-cell-mediated autoimmune processes are actively involved in the disease process of AS. So far, B cells have received relatively little attention in AS pathogenesis; this is largely due to a lack of conventional disease-defining autoantibodies. However, against prevailing dogma, there is a growing body of evidence suggestive of B cell involvement. This is illustrated by disturbances in circulating B cell populations and the formation of auto-reactive and non-autoreactive antibodies, along with B cell infiltrates within the axial skeleton of AS patients. Furthermore, the depletion of B cells, using rituximab, displayed beneficial results in a subgroup of patients with AS. This review provides an overview of our current knowledge of B cells in AS, and discusses their potential role in its pathogenesis. An overarching picture portrays increased B cell activation in AS, although it is unclear whether B cells directly affect pathogenesis, or are merely bystanders in the disease process.

Hydroxychloroquine induces oxidative DNA damage and mutation in mammalian cells

Since the early stages of the pandemic, hydroxychloroquine (HCQ), a widely used drug with good safety profile in clinic, has come to the forefront of research on drug repurposing for COVID-19 treatment/prevention. Despite the decades-long use of HCQ in the treatment of diseases, such as malaria and autoimmune disorders, the exact mechanisms of action of this drug are only beginning to be understood. To date, no data are available on the genotoxic potential of HCQ in vitro or in vivo. The present study is the first investigation of the DNA damaging- and mutagenic effects of HCQ in mammalian cells in vitro, at concentrations that are comparable to clinically achievable doses in patient populations. We demonstrate significant induction of a representative oxidative DNA damage (8-oxodG) in primary mouse embryonic fibroblasts (MEFs) treated with HCQ at 5 and 25 μM concentrations (P = 0.020 and P = 0.029, respectively), as determined by enzyme-linked immunosorbent assay. Furthermore, we show significant mutagenicity of HCQ, manifest as 2.2- and 1.8-fold increases in relative cII mutant frequency in primary and spontaneously immortalized Big Blue® MEFs, respectively, treated with 25 μM dose of this drug (P = 0.005 and P = 0.012, respectively). The observed genotoxic effects of HCQ in vitro, achievable at clinically relevant doses, are novel and important, and may have significant implications for safety monitoring in patient populations. Given the substantial number of the world's population receiving HCQ for the treatment of various chronic diseases or in the context of clinical trials for COVID-19, our findings warrant further investigations into the biological consequences of therapeutic/preventive use of this drug.

The transmembrane domain and luminal C-terminal region independently support invariant chain trimerization and assembly with MHCII into nonamers

Background

Invariant chain (CD74, Ii) is a multifunctional protein expressed in antigen presenting cells. It assists the ER exit of various cargos and serves as a receptor for the macrophage migration inhibitory factor. The newly translated Ii chains trimerize, a structural feature that is not readily understood in the context of its MHCII chaperoning function. Two segments of Ii, the luminal C-terminal region (TRIM) and the transmembrane domain (TM), have been shown to participate in the trimerization process but their relative importance and impact on the assembly with MHCII molecules remains debated. Here, we addressed the requirement of these domains in the trimerization of human Ii as well as in the oligomerization with MHCII molecules. We used site-directed mutagenesis to generate series of Ii and DR mutants. These were transiently transfected in HEK293T cells to test their cell surface expression and analyse their interactions by co-immunoprecipitations.

Results

Our results showed that the TRIM domain is not essential for Ii trimerization nor for intracellular trafficking with MHCII molecules. We also gathered evidence that in the absence of TM, TRIM allows the formation of multi-subunit complexes with HLA-DR. Similarly, in the absence of TRIM, Ii can assemble into high-order structures with MHCII molecules.

Conclusions

Altogether, our data show that trimerization of Ii through either TM or TRIM sustains nonameric complex formation with MHCII molecules.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-021-00444-6.

Partnering for the major histocompatibility complex class II and antigenic determinant requires flexibility and chaperons

Cytotoxic, or helper T cells recognize antigen via T cell receptors (TCRs) that can see their target antigen as short sequences of peptides bound to the groove of proteins of major histocompatibility complex (MHC) class I, and class II respectively. For MHC class II epitope selection from exogenous pathogens or self-antigens, participation of several accessory proteins, molecular chaperons, processing enzymes within multiple vesicular compartments is necessary. A major contributing factor is the MHC class II structure itself that uniquely offers a dynamic and flexible groove essential for epitope selection. In this review, I have taken a historical perspective focusing on the flexibility of the MHC II molecules as the driving force in determinant selection and interactions with the accessory molecules in antigen processing, HLA-DM and HLA-DO.

Nanocarrier vaccines for SARS-CoV-2

The SARS-CoV-2 global pandemic has seen rapid spread, disease morbidities and death associated with substantive social, economic and societal impacts. Treatments rely on re-purposed antivirals and immune modulatory agents focusing on attenuating the acute respiratory distress syndrome. No curative therapies exist. Vaccines remain the best hope for disease control and the principal global effort to end the pandemic. Herein, we summarize those developments with a focus on the role played by nanocarrier delivery.

Overcoming Chemoresistance: Altering pH of Cellular Compartments by Chloroquine and Hydroxychloroquine

Resistance to the anti-cancer effects of chemotherapeutic agents (chemoresistance) is a major issue for people living with cancer and their providers. A diverse set of cellular and inter-organellar signaling changes have been implicated in chemoresistance, but it is still unclear what processes lead to chemoresistance and effective strategies to overcome chemoresistance are lacking. The anti-malaria drugs, chloroquine (CQ) and its derivative hydroxychloroquine (HCQ) are being used for the treatment of various cancers and CQ and HCQ are used in combination with chemotherapeutic drugs to enhance their anti-cancer effects. The widely accepted anti-cancer effect of CQ and HCQ is their ability to inhibit autophagic flux. As diprotic weak bases, CQ and HCQ preferentially accumulate in acidic organelles and neutralize their luminal pH. In addition, CQ and HCQ acidify the cytosolic and extracellular environments; processes implicated in tumorigenesis and cancer. Thus, the anti-cancer effects of CQ and HCQ extend beyond autophagy inhibition. The present review summarizes effects of CQ, HCQ and proton pump inhibitors on pH of various cellular compartments and discuss potential mechanisms underlying their pH-dependent anti-cancer effects. The mechanisms considered here include their ability to de-acidify lysosomes and inhibit autophagosome lysosome fusion, to de-acidify Golgi apparatus and secretory vesicles thus affecting secretion, and to acidify cytoplasm thus disturbing aerobic metabolism. Further, we review the ability of these agents to prevent chemotherapeutic drugs from accumulating in acidic organelles and altering their cytosolic concentrations.

Insights of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2) pandemic: a current review

COVID-19, a pandemic of the 21st century caused by novel coronavirus SARS-CoV-2 was originated from China and shallowed world economy and human resource. The medical cures via herbal treatments, antiviral drugs, and vaccines still in progress, and studying rigorously. SARS-CoV-2 is more virulent than its ancestors due to evolution in the spike protein(s), mediates viral attachment to the host's membranes. The SARS-CoV-2 receptor-binding spike domain associates itself with human angiotensin-converting enzyme 2 (ACE-2) receptors. It causes respiratory ailments with irregularities in the hepatic, nervous, and gastrointestinal systems, as reported in humans suffering from COVID-19 and reviewed in the present article. There are several approaches, have been put forward by many countries under the world health organization (WHO) recommendations and some trial drugs were introduced for possible treatment of COVID-19, such as Lopinavir or Ritonavir, Arbidol, Chloroquine (CQ), Hydroxychloroquine (HCQ) and most important Remdesivir including other like Tocilizumab, Oritavancin, Chlorpromazine, Azithromycin, Baricitinib, etc. RT-PCR is the only and early detection test available besides the rapid test kit (serodiagnosis) used by a few countries due to unreasonable causes. Development of vaccine by several leader of pharmaceutical groups still under trial or waiting for approval for mass inoculation. Management strategies have been evolved by the recommendations of WHO, specifically important to control COVID-19 situations, in the pandemic era. This review will provide a comprehensive collection of studies to support future research and enhancement in our wisdom to combat COVID-19 pandemic and to serve humanity.

Diagnostic value of anti-CD74 antibodies in early and late axial spondyloarthritis and its relationship to disease activity

OBJECTIVES

This study was designed to evaluate the role of anti-CD74 antibodies in diagnosis of axial spondyloarthritis (axSpA) and their relationship to disease duration and disease activity.

METHODS

Fifty patients with axSpA, 15 patients with RA and 15 healthy subjects were included in the study. Clinical examination and laboratory tests were done. The ESR, CRP level and ASDAS were measured as markers of the disease activity. Quantitative determination of human CD74 IgG antibodies was done.

RESULTS

The mean age of the patients was 38.22 (S.D.12.20) years. The level of CD74 autoantibodies was significantly higher in axSpA in comparison to control groups. Most patients with positive articular and extra-articular manifestations were positive for CD74 autoantibodies. In patients with inactive disease, 33.3% were positive for CD74 autoantibodies, as were 83% with active disease. High percentages of patients with early and late axSPA were CD74 autoantibody positive. The majority of patients with positive disease activity in early and late axSpA were CD74 autoantibody positive. CD74 autoantibodies had 80% sensitivity vs both control groups with 87% specificity vs the healthy control group and 80% vs the RA control group in the diagnosis of axSpA.

CONCLUSIONS

The frequency of positive anti-CD74 IgG antibodies was as high in patients with early axSpA as in those with late axSpA, with no significant differences. There was a significant difference in the frequency of positive anti-CD74 IgG antibodies between patients with positive and negative disease activity. Based on the sensitivity and specificity of anti-CD74 IgG, this is a promising diagnostic tool to support the clinical diagnosis of axSpA.

Hydroxychloroquine in the COVID-19 pandemic era: in pursuit of a rational use for prophylaxis of SARS-CoV-2 infection

INTRODUCTION

Over the last few months, coronavirus disease 2019 (COVID-19) pandemic caused by the novel coronavirus SARS-CoV-2 has posed a serious threat to public health on a global scale. Given the current lack of an effective vaccine, several drugs have been repurposed for treatment and prophylaxis of COVID-19 in an attempt to find an effective cure.

AREAS COVERED

The antimalarial drug hydroxychloroquine (HCQ) initially garnered widespread attention following the publication of preliminary results showing that this drug exerts an anti-SARS-CoV-2 activity in vitro.

EXPERT OPINION

To date, clinical evidence suggests lack of benefit from HCQ use for the treatment of hospitalized patients with COVID-19. In such patients, HCQ also appears to be associated with an increased risk of QT interval prolongation and potentially lethal ventricular arrhythmias. Therefore, FDA has recently revoked the Emergency Use Authorization (EUA) for emergency use of HCQ and chloroquine to treat COVID-19. Conversely, whether HCQ use may represent an effective prophylactic strategy against COVID-19 is a separate question that still remains to be answered. In addition, relevant aspects regarding the potential risks and benefits of HCQ need to be clarified, in pursuit of a rational use of this drug in the COVID-19 pandemic era.

Malaria and COVID-19: unmasking their ties

The incidence and mortality of COVID-19, according to the World Health Organization reports, shows a noticeable difference between North America, Western Europe, and South Asia on one hand and most African countries on the other hand, especially the malaria-endemic countries. Although this observation could be attributed to limited testing capacity, mitigation tools adopted and cultural habits, many theories have been postulated to explain this difference in prevalence and mortality. Because death tends to occur more in elders, both the role of demography, and how the age structure of a population may contribute to the difference in mortality rate between countries were discussed. The variable distribution of the ACEI/D and the ACE2 (C1173T substitution) polymorphisms has been postulated to explain this variable prevalence. Up-to-date data regarding the role of hydroxychloroquine (HCQ) and chloroquine (CQ) in COVID-19 have been summarized. The article also sheds lights on how the similarity of malaria and COVID-19 symptoms can lead to misdiagnosis of one disease for the other or overlooking the possibility of co-infection. As the COVID-19 pandemic threatens the delivery of malaria services, such as the distribution of insecticide-treated nets (ITNs), indoor residual spraying, as well as malaria chemoprevention there is an urgent need for rapid and effective responses to avoid malaria outbreaks.

Update on treatment and preventive interventions against COVID-19: an overview of potential pharmacological agents and vaccines

The outbreak of coronavirus disease 2019 (COVID-19) triggered by the new member of the coronaviridae family, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has created an unprecedented challenge for global health. In addition to mild to moderate clinical manifestations such as fever, cough, and fatigue, severe cases often developed lethal complications including acute respiratory distress syndrome (ARDS) and acute lung injury. Given the alarming rate of infection and increasing trend of mortality, the development of underlying therapeutic and preventive treatment, as well as the verification of its effectiveness, are the top priorities. Current research mainly referred to and evaluated the application of the empirical treatment based on two precedents, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), including antiviral drugs targeting different stages of virus replication, immunotherapy modulating the overactivated inflammation response, and other therapies such as herbal medicine and mesenchymal stem cells. Besides, the ongoing development of inventing prophylactic interventions such as various vaccines by companies and institutions worldwide is crucial to decline morbidity and mortality. This review mainly focused on promising candidates for the treatment of COVID-19 and collected recently updated evidence relevant to its feasibility in clinical practice in the near future.

Advances in the use of chloroquine and hydroxychloroquine for the treatment of COVID-19

Coronavirus Disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is spreading worldwide. Antiviral therapy is the most important treatment for COVID-19. Among the drugs under investigation, anti-malarials, chloroquine (CQ) and hydroxychloroquine (HCQ), are being repurposed as treatment for COVID-19. CQ/HCQ were shown to prevent receptor recognition by coronaviruses, inhibit endosome acidification, which interferes with membrane fusion, and exhibit immunomodulatory activity. These multiple mechanisms may work together to exert a therapeutic effect on COVID-19. A number of in vitro studies revealed inhibitory effects of CQ/HCQ on various coronaviruses, including SARS-CoV-2 although conflicting results exist. Several clinical studies showed that CQ/HCQ alone or in combination with a macrolide may alleviate the clinical symptoms of COVID-19, promote viral conversion, and delay disease progression, with less serious adverse effects. However, recent studies indicated that the use of CQ/HCQ, alone or in combination with a macrolide, did not show any favorable effect on patients with COVID-19. Adverse effects, including prolonged QT interval after taking CQ/HCQ, may develop in COVID-19 patients. Therefore, current data are not sufficient enough to support the use of CQ/HCQ as therapies for COVID-19 and increasing caution should be taken about the application of CQ/HCQ in COVID-19 before conclusive findings are obtained by well-designed, multi-center, randomized, controlled studies.

Janus sword actions of chloroquine and hydroxychloroquine against COVID-19

Chloroquine (CQ) and its analogue hydroxychloroquine (HCQ) have been thrust into our everyday vernacular because some believe, based on very limited basic and clinical data, that they might be helpful in preventing and/or lessening the severity of the pandemic coronavirus disease 2019 (COVID-19). However, lacking is a temperance in enthusiasm for their possible use as well as sufficient perspective on their effects and side-effects. CQ and HCQ have well-known properties of being diprotic weak bases that preferentially accumulate in acidic organelles (endolysosomes and Golgi apparatus) and neutralize luminal pH of acidic organelles. These primary actions of CQ and HCQ are responsible for their anti-malarial effects; malaria parasites rely on acidic digestive vacuoles for survival. Similarly, de-acidification of endolysosomes and Golgi by CQ and HCQ may block severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) integration into host cells because SARS-CoV-2 may require an acidic environment for its entry and for its ability to bud and infect bystander cells. Further, de-acidification of endolysosomes and Golgi may underly the immunosuppressive effects of these two drugs. However, modern cell biology studies have shown clearly that de-acidification results in profound changes in the structure, function and cellular positioning of endolysosomes and Golgi, in signaling between these organelles and other subcellular organelles, and in fundamental cellular functions. Thus, studying the possible therapeutic effects of CQ and HCQ against COVID-19 must occur concurrent with studies of the extent to which these drugs affect organellar and cell biology. When comprehensively examined, a better understanding of the Janus sword actions of these and other drugs might yield better decisions and better outcomes.

Current Status of Multiple Drug Molecules, and Vaccines: An Update in SARS-CoV-2 Therapeutics

The coronavirus disease of 2019 (COVID-19) is a pandemic disease that has taken the lives of many around the world. It is caused by severe acute respiratory syndrome-corona virus-2 (SARS-CoV-2). To date, the USA, Italy, Spain, France, Russia, and the UK have been hit the hardest by the virus. However, death counts are still rising. Some nations have managed to “flatten” the death rate via protective measures such physical distancing, quarantine measures, and therapeutic management. The structure of the SARS-CoV-2 virus comprises of S proteins, M proteins, E proteins, hemagglutinin esterases, nucleocapsid proteins, and a 30-kb RNA genome. Viral proteases cleave these polyproteins and RNA-dependent polymerases replicate the genome. Currently, there are no effective therapies against this new disease. Numerous investigators are developing novel protease inhibitors, some of which have made it into clinical trials. Researchers are also attempting to develop a vaccine. In this review paper, we discuss the latest therapeutic developments against COVID-19.

Beyond Anti-viral Effects of Chloroquine/Hydroxychloroquine

As the world is severely affected by COVID-19 pandemic, the use of chloroquine and hydroxychloroquine in prevention or for the treatment of patients is allowed in multiple countries but remained at the center of much controversy in recent days. This review describes the properties of chloroquine and hydroxychloroquine, and highlights not only their anti-viral effects but also their important immune-modulatory properties and their well-known use in autoimmune diseases, including systemic lupus and arthritis. Chloroquine appears to inhibit in vitro SARS virus' replication and to interfere with SARS-CoV2 receptor (ACE2). Chloroquine and hydroxychloroquine impede lysosomal activity and autophagy, leading to a decrease of antigen processing and presentation. They are also known to interfere with endosomal Toll-like receptors signaling and cytosolic sensors of nucleic acids, which result in a decreased cellular activation and thereby a lower type I interferons and inflammatory cytokine secretion. Given the antiviral and anti-inflammatory properties of chloroquine and hydroxychloroquine, there is a rational to use them against SARS-CoV2 infection. However, the anti-interferon properties of these molecules might be detrimental, and impaired host immune responses against the virus. This duality could explain the discrepancy with the recently published studies on CQ/HCQ treatment efficacy in COVID-19 patients. Moreover, although these treatments could be an interesting potential strategy to limit progression toward uncontrolled inflammation, they do not appear per se sufficiently potent to control the whole inflammatory process in COVID-19, and more targeted and/or potent therapies should be required at least in add-on.

COVID-19: a recommendation to examine the effect of hydroxychloroquine in preventing infection and progression

A novel coronavirus disease (COVID-19), caused by infection with SARS-CoV-2, has swept across 31 provinces in China and over 40 countries worldwide. The transition from first symptoms to acute respiratory distress syndrome (ARDS) is highly likely to be due to uncontrolled cytokine release. There is an urgent need to identify safe and effective drugs for treatment. Chloroquine (CQ) exhibits a promising inhibitory effect. However, the clinical use of CQ can cause severe side effects. We propose that hydroxychloroquine (HCQ), which exhibits an antiviral effect highly similar to that of CQ, could serve as a better therapeutic approach. HCQ is likely to attenuate the severe progression of COVID-19, inhibiting the cytokine storm by suppressing T cell activation. It has a safer clinical profile and is suitable for those who are pregnant. It is cheaper and more readily available in China. We herein strongly urge that clinical trials are performed to assess the preventive effects of HCQ in both disease infection and progression.

COVID-19: a recommendation to examine the effect of hydroxychloroquine in preventing infection and progression

A novel coronavirus disease (COVID-19), caused by infection with SARS-CoV-2, has swept across 31 provinces in China and over 40 countries worldwide. The transition from first symptoms to acute respiratory distress syndrome (ARDS) is highly likely to be due to uncontrolled cytokine release. There is an urgent need to identify safe and effective drugs for treatment. Chloroquine (CQ) exhibits a promising inhibitory effect. However, the clinical use of CQ can cause severe side effects. We propose that hydroxychloroquine (HCQ), which exhibits an antiviral effect highly similar to that of CQ, could serve as a better therapeutic approach. HCQ is likely to attenuate the severe progression of COVID-19, inhibiting the cytokine storm by suppressing T cell activation. It has a safer clinical profile and is suitable for those who are pregnant. It is cheaper and more readily available in China. We herein strongly urge that clinical trials are performed to assess the preventive effects of HCQ in both disease infection and progression.

Facts and Myths: Efficacies of Repurposing Chloroquine and Hydroxychloroquine for the Treatment of COVID-19

The emergence of coronavirus disease 2019 (COVID-19) is caused by the 2019 novel coronavirus (2019-nCoV). The 2019-nCoV first broke out in Wuhan and subsequently spread worldwide owing to its extreme transmission efficiency. The fact that the COVID-19 cases and mortalities are reported globally and the WHO has declared this outbreak as the pandemic, the international health authorities have focused on rapid diagnosis and isolation of patients as well as search for therapies able to counter the disease severity. Due to the lack of known specific, effective and proven therapies as well as the situation of public-health emergency, drug repurposing appears to be the best armour to find a therapeutic solution against 2019-nCoV infection. Repurposing anti-malarial drugs and chloroquine (CQ)/ hydroxychloroquine (HCQ) have shown efficacy to inhibit most coronaviruses, including SARS-CoV-1 coronavirus. These CQ analogues have shown potential efficacy to inhibit 2019-nCoV in vitro that leads to focus several future clinical trials. This review discusses the possible effective roles and mechanisms of CQ analogues for interfering with the 2019-nCoV replication cycle and infection.

Therapeutic use of chloroquine and hydroxychloroquine in COVID-19 and other viral infections: A narrative review

The rapidly spreading Coronavirus Disease (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus (SARS-CoV-2), represents an unprecedented serious challenge to the global public health community. The extremely rapid international spread of the disease with significant morbidity and mortality made finding possible therapeutic interventions a global priority. While approved specific antiviral drugs against SARS-CoV-2 are still lacking, a large number of existing drugs are being explored as a possible treatment for COVID-19 infected patients. Recent publications have re-examined the use of Chloroquine (CQ) and/or Hydroxychloroquine (HCQ) as a potential therapeutic option for these patients. In an attempt to explore the evidence that supports their use in COVID-19 patients, we comprehensively reviewed the previous studies which used CQ or HCQ as an antiviral treatment. Both CQ and HCQ demonstrated promising in vitro results, however, such data have not yet been translated into meaningful in vivo studies. While few clinical trials have suggested some beneficial effects of CQ and HCQ in COVID-19 patients, most of the reported data are still preliminary. Given the current uncertainty, it is worth being mindful of the potential risks and strictly rationalise the use of these drugs in COVID-19 patients until further high quality randomized clinical trials are available to clarify their role in the treatment or prevention of COVID-19.

Mechanisms of action of hydroxychloroquine and chloroquine: implications for rheumatology

Despite widespread clinical use of antimalarial drugs such as hydroxychloroquine and chloroquine in the treatment of rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and other inflammatory rheumatic diseases, insights into the mechanism of action of these drugs are still emerging. Hydroxychloroquine and chloroquine are weak bases and have a characteristic 'deep' volume of distribution and a half-life of around 50 days. These drugs interfere with lysosomal activity and autophagy, interact with membrane stability and alter signalling pathways and transcriptional activity, which can result in inhibition of cytokine production and modulation of certain co-stimulatory molecules. These modes of action, together with the drug's chemical properties, might explain the clinical efficacy and well-known adverse effects (such as retinopathy) of these drugs. The unknown dose-response relationships of these drugs and the lack of definitions of the minimum dose needed for clinical efficacy and what doses are toxic pose challenges to clinical practice. Further challenges include patient non-adherence and possible context-dependent variations in blood drug levels. Available mechanistic data give insights into the immunomodulatory potency of hydroxychloroquine and provide the rationale to search for more potent and/or selective inhibitors.

In Vitro Digestion with Proteases Producing MHC Class II Ligands

Proteases generate peptides that bind to MHC class II molecules to interact with a wide diversity of CD4⁺ T cells. They are expressed in dedicated organelles: endosomes and lysosomes of professional antigen-presenting cells (pAPCs) such as B cells, macrophages, and dendritic cells. The identification of endosomal proteases which produce antigenic peptides is important for example for better vaccination and to prevent autoimmune diseases. Here, we describe a panel of techniques (in vitro digestion assays of protein with recombinant proteases or purified endosomes/lysosomes, T cell stimulation) to monitor the production of MHC class II ligands.

Anti-malarial drugs: possible mechanisms of action in autoimmune disease and prospects for drug development

A wide variety of mechanisms of anti-rheumatic action have been proposed for antimalarial agents. The molecular actions of chloroquine have been most thoroughly studied in vitro and in vivo, but it is likely that hydroxychloroquine works by a similar mechanism. Both agents are weak diprotic bases that can pass through the lipid cell membrane and preferentially concentrate in acidic cyto-plasmic vesicles. The resulting slight elevation of pH within these vesicles in macrophages or other antigen-presenting cells may influence the immune response to autoantigens. We hypothesize that anti-malarial agents influence the association of autoantigenic peptides with class II MHC molecules in the compartment for peptide loading and/or the subsequent processing and transport of the peptide-MHC complex to the cell membrane. This model of anti-malarial action provides a method to test additional drugs for their ability to modulate the immune response.

Mechanism of Action of Antimalarial Drugs: Inhibition of Antigen Processing and Presentation

Recent studies have elucidated the steps involved in the association of antigenic peptides with major histocompatibility complex (MHC) encoded proteins and have suggested how antimalarial compounds might influence this important site of immune activation. These steps of antigen presentation in the macrophage (or other antigen-presenting cells) include: (a) the partial proteolytic degradation of endogenous and exogenous proteins into peptides within the lysosome; (b) the synthesis of MHC class II (i.e. HLA-D associated) α, β, and invariant (Ii) chains in the endoplasmic reticulum; (c) the initial association of α-Ii and β-li chains in the endoplasmic reticulum and the transport of these complexes to the primary endosome; (d) the fusion of lysosomal vacuoles and endosomal vacuoles, allowing the mixtures of lysosomal enzymes, peptides, α–Ii and β–Ii; (e) the displacement of Ii chains by peptides to form α–β–peptide complexes in the endosome; and (f) the migration of α–β–peptide complexes to the macrophage cell surface where they can stimulate CD4 T cells, resulting in release of cytokines. A low pH is required for digestion of the protein by acidic hydrolases in the lysosome, for assembly of the α–β–peptide complex and for its transport to the cell surface. Chloroquine and hydroxychloroquine are weak diprotic bases that can diffuse across the cell membrane and raise the pH within cell vesicles. This background provides the underlying basis for the theory that antimalarials may act to prevent autoimmunity by the following putative mechanism. Antimalarial compounds may: (a) stabilize the α-Ii and β-Ii interactions and prevent low-affinity peptides from forming α–β–peptide complexes; and (b) interfere with the efficient movement of α-Ii, β-Ii and α–β–peptide complexes to the correct locations within the cell cytoplasm or to the cell surfaces. Decreased presentation of autoantigenic peptides by macrophages might then lead to downregulation of autoimmune CD4+ T cells and diminish release of cytokines associated with clinical and laboratory signs of autoimmune disease.

Modified MHC Class II-Associated Invariant Chain Induces Increased Antibody Responses against Plasmodium falciparum Antigens after Adenoviral Vaccination

Adenoviral vectors can induce T and B cell immune responses to Ags encoded in the recombinant vector. The MHC class II invariant chain (Ii) has been used as an adjuvant to enhance T cell responses to tethered Ag encoded in adenoviral vectors. In this study, we modified the Ii adjuvant by insertion of a furin recognition site (Ii-fur) to obtain a secreted version of the Ii. To test the capacity of this adjuvant to enhance immune responses, we recombined vectors to encode Plasmodium falciparum virulence factors: two cysteine-rich interdomain regions (CIDR) α1 (IT4var19 and PFCLINvar30 var genes), expressed as a dimeric Ag. These domains are members of a highly polymorphic protein family involved in the vascular sequestration and immune evasion of parasites in malaria. The Ii-fur molecule directed secretion of both Ags in African green monkey cells and functioned as an adjuvant for MHC class I and II presentation in T cell hybridomas. In mice, the Ii-fur adjuvant induced a similar T cell response, as previously demonstrated with Ii, accelerated and enhanced the specific Ab response against both CIDR Ags, with an increased binding capacity to the cognate endothelial protein C receptor, and enhanced the breadth of the response toward different CIDRs. We also demonstrate that the endosomal sorting signal, secretion, and the C-terminal part of Ii were needed for the full adjuvant effect for Ab responses. We conclude that engineered secretion of Ii adjuvant-tethered Ags establishes a single adjuvant and delivery vehicle platform for potent T and B cell-dependent immunity.

A personal retrospective on the mechanisms of antigen processing

My intention here is to describe the history of the molecular aspects of the antigen processing field from a personal perspective, beginning with the early identification of the species that we now know as MHC class I and MHC class II molecules, to the recognition that their stable surface expression and detection by T cells depends on peptide association, and to the unraveling of the biochemical and cell biological mechanisms that regulate peptide binding. One goal is to highlight the role that serendipity or, more colloquially, pure blind luck can play in advancing the research enterprise when it is combined with an appropriately receptive mind. This is not intended to be an overarching review, and because of my own work I focus primarily on studies of the human MHC. This means that I neglect the work of many other individuals who made advances in other species, particularly those who produced the many knockout mouse strains used to demonstrate the importance of the antigen processing machinery for initiating immune responses. I apologize in advance to colleagues around the globe whose contributions I deal with inadequately for these reasons, and to those whose foundational work is now firmly established in text books and therefore not cited. So many individuals have worked to advance the field that giving all of them the credit they deserve is almost impossible. I have attempted, while focusing on work from my own laboratory, to point out contemporaneous or sometimes earlier advances made by others. Much of the success of my own laboratory came because we simultaneously worked on both the MHC class I and class II systems and used the findings in one area to inform the other, but mainly it depended on the extraordinary group of students and fellows who have worked on these projects over the years. To those who worked in other areas who are not mentioned here, rest assured that I appreciate your efforts just as much.

Invariant chain p41 mediates production of soluble MHC class II molecules

Major histocompatibility complex class II (MHC II) molecules are mainly expressed on antigen presentation cells and play an important role in immune response. It has been reported that MHC II molecules are also detected in serum as a soluble form (sMHC II molecules), and they are considered to be involved in the maintenance of self-tolerance. However, the mechanism by which sMHC II molecules are produced remains unclear. Invariant chain (Ii), also called CD74, plays an important role in antigen presentation of MHC II molecules. In the present study, we analyzed the role of Ii on the production of sMHC II molecules. We found that the amount of sMHC II molecules in serum was decreased in Ii-deficient mice compared to wild-type mice. sMHC II molecules were secreted from cells transfected with MHC II molecules and Ii but not from cells transfected with MHC II molecules alone. Moreover, isoform p41 of Ii-transfected cells induced more sMHC II molecules compared to isoform p31-transfected cells. The molecular weight of sMHC II molecules from MHC II and Ii p41-transfected cells was approximately 60 kDa, indicating that sMHC II molecules are a single heterodimer of α and β chains that is not associated with micro-vesicles. From the analysis of Ii-deletion mutants, we found that the luminal domain of Ii p41 is crucial for the production of sMHC II molecules. These results suggested that Ii has an important role in production of sMHC II molecules.

Autoantibodies in Spondyloarthritis, Focusing on Anti-CD74 Antibodies

Spondyloarthritis (SpA) is an inflammatory rheumatic disease with diverse clinical presentation. The diagnosis of SpA remains a big challenge in daily clinical practice because of the limitation in specific biomarkers of SpA, more biomarkers are still needed for SpA diagnosis and disease activity monitoring. In the past, SpA was considered predominantly as auto-inflammatory disease vs. autoimmune disease. However, in recent years several researches demonstrated a broad autoantibody response in SpA patients. Study also indicated that mice lack of ZAP70 in T cell develop SpA featured inflammation. These studies indicated the autoimmune features of SpA and gave rise to the potential use of autoantibody in SpA management. In this article, we reviewed recent reports of autoantibodies associated with SpA patients, revealing the autoimmune features of SpA, suggesting the hypothesis that SpA was also an autoimmune disease, studies about the autoimmune features might provide more insights in the pathogenesis of SpA. In addition, as there are two opposite conclusions in the role of anti-CD74 autoantibody in the diagnosis of SpA, we also gave our own data on the diagnostic value of anti-CD74 in Chinese SpA patients. Though our data indicated that anti-CD74 might not be a good biomarker for SpA diagnosis in Asian people, CD74 was still a good molecule target in the research of SpA pathogenesis.

Role of membrane environment and membrane-spanning protein regions in assembly and function of the Class II Major Histocompatibility complex

Class II Major Histocompatibility complex (MHC-II) is a polymorphic heterodimer that binds antigen-derived peptides and presents them on the surface of antigen presenting cells. This mechanism of antigen presentation leads to recognition by CD4 T-cells and T-cell activation, making it a critical element of adaptive immune response. For this reason, the structural determinants of MHC-II function have been of great interest for the past 30 years, resulting in a robust structural understanding of the extracellular regions of the complex. However, the membrane-localized regions have also been strongly implicated in protein-protein and protein-lipid interactions that facilitate Class II assembly, transport and function, and it is these regions that are the focus of this review. Here we describe studies that reveal the strong and selective interactions between the transmembrane domains of the MHC α, and invariant chains which, when altered, have broad reaching impacts on antigen presentation and Class II function. We also summarize work that clearly demonstrates the link between membrane lipid composition (particularly the presence of cholesterol) and MHC-II conformation, subsequent peptide binding, and downstream T-cell activation. We have integrated these studies into a comprehensive view of Class II transmembrane domain biology.

Class II MHC antigen processing in immune tolerance and inflammation

Presentation of peptide antigens by MHC-II proteins is prerequisite to effective CD4 T cell tolerance to self and to recognition of foreign antigens. Antigen uptake and processing pathways as well as expression of the peptide exchange factors HLA-DM and HLA-DO differ among the various professional and non-professional antigen-presenting cells and are modulated by cell developmental state and activation. Recent studies have highlighted the importance of these cell-specific factors in controlling the source and breadth of peptides presented by MHC-II under different conditions. During inflammation, increased presentation of selected self-peptides has implications for maintenance of peripheral tolerance and autoimmunity.

Longitudinal analysis of tear cathepsin S activity levels in male non-obese diabetic mice suggests its potential as an early stage biomarker of Sjögren's Syndrome

CONTEXT

Cathepsin S (CTSS) activity is elevated in Sjögren's Syndrome (SS) patient tears.

OBJECTIVE

To evaluate longitudinal expression of tear and tissue CTSS activity relative to other disease indicators in Non-Obese Diabetic (NOD) mice.

METHODS

CTSS activity was measured in tears and lacrimal glands (LG) from male 1-6 month (M) NOD and 1 and 6 M BALB/c mice. Lymphocytic infiltration was quantified by histopathology, while disease-related proteins (Rab3D, CTSS, collagen 1) were quantified using q-PCR and immunofluorescence.

RESULTS

In NOD LG, lymphocytic infiltration was noted by 2 M and established by 3 M (p < 0.01). IFN-ɣ, TNF-α, and MHC II expression were increased by 2 M (p < 0.01). Tear CTSS activity was significantly elevated at 2 M (p < 0.001) to a maximum of 10.1-fold by 6 M (p < 0.001). CTSS activity in LG lysates was significantly elevated by 2 M (p < 0.001) to a maximum of 14-fold by 3 M (p < 0.001). CTSS and Rab3D immunofluorescence were significantly increased and decreased maximally in LG acini by 3 M and 2 M, respectively. Comparable changes were not detected between 1 and 6 M BALB/c mouse LG, although Collagen 1 was decreased by 6 M in LG of both strains.

CONCLUSION

Tear CTSS activity is elevated with other early disease indicators, suggesting potential as an early stage biomarker for SS.

MHC class II alpha, beta and MHC class II-associated invariant chains from Chinese sturgeon (Acipenser sinensis) and their response to immune stimulation

The major histocompatibility complex class II (MHC II) molecules play a vital role in adaptive immune response through presenting antigenic peptides to CD4⁺ T lymphocytes. To accomplish this physiologic function, the MHC class II-associated invariant chain interacts with the MHC II α/β subunits and promotes their correct assembly and efficient traffic. Here, we isolated the cDNAs of MHC II α, β and MHC II-associated invariant chains (designated as CsMHC II α, CsMHC II β, and CsMHC II γ) from Chinese sturgeon (Acipenser sinensis). The CsMHC II α, β, and γ mRNAs were widely expressed in Chinese sturgeon, and the highest expression was found in spleen for CsMHC II α and β chains, while in head kidney for CsMHC II γ chain. Stimulation to Chinese sturgeon with inactivated trivalent bacterial vaccine or polyinosinic polycytidylic acid (poly(I:C)) up-regulated the expressions of CsMHC II α, and β mRNAs, and their transcripts were overall more quickly up-regulated by poly(I:C) than by bacterial vaccine. Poly(I:C) induced higher CsMHC II γ expression than bacterial vaccine in intestine and spleen, while lower than bacterial vaccine in head kidney and liver. When co-expressed in mouse dendritic cells, the CsMHC II γ chain bound to both the MHC II α and β chains. Furthermore, the over-expressed CsMHC II γ chain, not CsMHC II α or CsMHC II β chain, activated NF-κB and STAT3 in mouse dendritic cells, and induced TNF-α and IL-6 expressions as well. This activity was nearly abolished by mutation of the Ser29/Ser34 to Ala29/Ala34 in CsMHC II γ. These results suggested that CsMHC II α, β, and γ chains might play important role in immune response to pathogen microbial infection of Chinese sturgeon possibly via a conserved functional mechanism throughout vertebrate evolution, which might contribute to our understanding the immune biology of sturgeons.

A cell-based high-throughput screening assay system for inhibitor compounds of antigen presentation by HLA class II molecule

A number of autoimmune diseases are associated with the genotypes of human leukocyte antigen class II (HLA), some of which present peptides derived from self-proteins, resulting in clonal expansion of self-reactive T cells. Therefore, selective inhibition of self-peptide loading onto such disease-associated HLA could ameliorate the diseases. To effectively identify such compounds, in this study, we established, for the first time, a cell- and 96-well microplate-based high-throughput screening system for inhibitors of antigen presentation. A panel of DRB1 genes plus DRA*01:01 gene were expressed in HEK293T cells and in 3T3 cells, and their binding with biotinylated known self-antigen peptides was measured by flow cytometry. HLA-DR1 (DRB1*01:01) and DR15 (DRB1*15:01) showed a high affinity with myelin basic protein peptide (MBP83-98). Therefore, in 96-well plate wells, MBP83-99 was allowed to bind to DR1 or DR15 on 3T3 cells in competition with a test compound, and the HLA-bound peptide was detected by streptavidin-conjugated β-galactosidase, thereby identifying inhibitor compounds for rheumatoid arthritis or multiple sclerosis. Our assay system has a potential for broad applications, including designing peptide vaccines.

Mechanistic understanding and significance of small peptides interaction with MHC class II molecules for therapeutic applications

Major histocompatibility complex (MHC) class II molecules are expressed by antigen-presenting cells and stimulate CD4(+) T cells, which initiate humoral immune responses. Over the past decade, interest has developed to therapeutically impact the peptides to be exposed to CD4(+) T cells. Structurally diverse small molecules have been discovered that act on the endogenous peptide exchanger HLA-DM by different mechanisms. Exogenously delivered peptides are highly susceptible to proteolytic cleavage in vivo; however, it is only when successfully incorporated into stable MHC II-peptide complexes that these peptides can induce an immune response. Many of the small molecules so far discovered have highlighted the molecular interactions mediating the formation of MHC II-peptide complexes. As potential drugs, these small molecules open new therapeutic approaches to modulate MHC II antigen presentation pathways and influence the quality and specificity of immune responses. This review briefly introduces how CD4(+) T cells recognize antigen when displayed by MHC class II molecules, as well as MHC class II-peptide-loading pathways, structural basis of peptide binding and stabilization of the peptide-MHC complexes. We discuss the concept of MHC-loading enhancers, how they could modulate immune responses and how these molecules have been identified. Finally, we suggest mechanisms whereby MHC-loading enhancers could act upon MHC class II molecules.

Antigen Processing and Presentation Mechanisms in Myeloid Cells

Unlike B cells, CD8-positive and CD4-positive T cells of the adaptive immune system do not recognize intact foreign proteins but instead recognize polypeptide fragments of potential antigens. These antigenic peptides are expressed on the surface of antigen presenting cells bound to MHC class I and MHC class II proteins. Here, we review the basics of antigen acquisition by antigen presenting cells, antigen proteolysis into polypeptide fragments, antigenic peptide binding to MHC proteins, and surface display of both MHC class I-peptide and MHC class II-peptide complexes.

La Deletion from Mouse Brain Alters Pre-tRNA Metabolism and Accumulation of Pre-5.8S rRNA, with Neuron Death and Reactive Astrocytosis

Human La antigen (Sjögren's syndrome antigen B [SSB]) is an abundant multifunctional RNA-binding protein. In the nucleoplasm, La binds to and protects from 3' exonucleases, the ends of precursor tRNAs, and other transcripts synthesized by RNA polymerase III and facilitates their maturation, while a nucleolar isoform has been implicated in rRNA biogenesis by multiple independent lines of evidence. We showed previously that conditional La knockout (La cKO) from mouse cortex neurons results in defective tRNA processing, although the pathway(s) involved in neuronal loss thereafter was unknown. Here, we demonstrate that La is stably associated with a spliced pre-tRNA intermediate. Microscopic evidence of aberrant nuclear accumulation of 5.8S rRNA in La cKO is supported by a 10-fold increase in a pre-5.8S rRNA intermediate. To identify pathways involved in subsequent neurodegeneration and loss of brain mass in the cKO cortex, we employed mRNA sequencing (mRNA-Seq), immunohistochemistry, and other approaches. This revealed robust enrichment of immune and astrocyte reactivity in La cKO cortex. Immunohistochemistry, including temporal analyses, demonstrated neurodegeneration, followed by astrocyte invasion associated with immune response and decreasing cKO cortex size over time. Thus, deletion of La from postmitotic neurons results in defective pre-tRNA and pre-rRNA processing and progressive neurodegeneration with loss of cortical brain mass.

Dynamic Changes in the Intracellular Association of Selected Rab Small GTPases with MHC Class II and DM during Dendritic Cell Maturation

Antigen processing for presentation by major histocompatibility complex class II (MHCII) molecules requires the latter to travel through the endocytic pathway together with its chaperons: the invariant chain (Ii) and DM. Nevertheless, the nature of the compartments where MHCII molecules travel to acquire peptides lacks definition regarding molecules involved in intracellular vesicular trafficking, such as Rab small GTPases. We aimed to define which Rab proteins are present during the intracellular transport of MHCII, DM, and Ii through the endocytic pathway on their route to the cell surface during dendritic cell (DC) maturation. We examined, by means of three-color confocal microscopy, the association of MHCII, DM, and Ii with Rab5, Rab7, Rab9, and Rab11 during the maturation of bone marrow-derived or spleen DC in response to LPS as an inflammatory stimulus. Prior to the stage of immature DC, MHCII migrated from diffuse small cytoplasmic vesicles, predominantly Rab5+Rab7- and Rab5+Rab7+ into a pericentriolar Rab5+Rab7+Rab9+ cluster, with Rab11+ areas. As DC reached the mature phenotype, MHCII left the pericentriolar endocytic compartments toward the cell surface in Rab11+ and Rab9+Rab11+ vesicles. The invariant chain and MHCII transport pathways were not identical. DM and MHCII appeared to arrive to pericentriolar endocytic compartments of immature DC through partially different routes. The association of MHCII molecules with distinct Rab GTPases during DC maturation suggests that after leaving the biosynthetic pathway, MHCII sequentially traffic from typical early endosomes to multivesicular late endosomes to finally arrive at the cell surface in Rab11+ recycling-type endosomes. In immature DCs, DM encounters transiently MHCII in the Rab5+Rab7+Rab9+ compartments, to remain there in mature DC.