SREC-I, a type F scavenger receptor, is an endocytic receptor for calreticulin

Structure of scavenger receptor SCARF1 and its interaction with lipoproteins

SCARF1 (scavenger receptor class F member 1, SREC-1 or SR-F1) is a type I transmembrane protein that recognizes multiple endogenous and exogenous ligands such as modified low-density lipoproteins (LDLs) and is important for maintaining homeostasis and immunity. But the structural information and the mechanisms of ligand recognition of SCARF1 are largely unavailable. Here, we solve the crystal structures of the N-terminal fragments of human SCARF1, which show that SCARF1 forms homodimers and its epidermal growth factor (EGF)-like domains adopt a long-curved conformation. Then, we examine the interactions of SCARF1 with lipoproteins and are able to identify a region on SCARF1 for recognizing modified LDLs. The mutagenesis data show that the positively charged residues in the region are crucial for the interaction of SCARF1 with modified LDLs, which is confirmed by making chimeric molecules of SCARF1 and SCARF2. In addition, teichoic acids, a cell wall polymer expressed on the surface of gram-positive bacteria, are able to inhibit the interactions of modified LDLs with SCARF1, suggesting the ligand binding sites of SCARF1 might be shared for some of its scavenging targets. Overall, these results provide mechanistic insights into SCARF1 and its interactions with the ligands, which are important for understanding its physiological roles in homeostasis and the related diseases.

Transcriptome profiling of macrophages persistently infected with human respiratory syncytial virus and effect of recombinant Taenia solium calreticulin on immune-related genes

Introduction

Human respiratory syncytial virus (hRSV) is a main cause of bronchiolitis in infants and its persistence has been described in immunocompromised subjects. However, limited evidence has been reported on the gene expression triggered by the hRSV and the effect of recombinant Taenia solium-derived calreticulin (rTsCRT).

Methods

Using a comprehensive microarray approach, we analyzed the transcriptome profile of a macrophage cell line that has supported hRSV persistence for over 150 passages. We compared the gene expression of persistently infected and non-infected macrophages. We also evaluated the effect of rTsCRT on hRSV-infected macrophage gene transcription, as well as on cytokine production and number of copies of the persistent hRSV genome.

Results

Our analysis showed that hRSV long-term virus infection significantly alters mRNA expression of antiviral, inflammatory, as well as arginine and lipid metabolism-associated genes, revealing a transcriptional signature that suggests a mixed M1/M2 phenotype. The resulting host-virus equilibrium allows for the regulation of viral replication, while evading the antiviral and proinflammatory responses. Interestingly, rTsCRT stimulus upregulated Tnfα, Il6 and Nos2 mRNA. We found increased levels of both proinflammatory cytokines and nitrite levels in the conditioned media of persistent macrophages treated with rTsCRT. This increase was associated with a significant reduction in viral genome copies.

Discussion

hRSV persistently infected macrophages retain responsiveness to external stimuli and demonstrate that the profound changes induced by viral persistence are potentially reversible. Our observations contribute to the understanding of the mechanisms related to hRSV persistence in macrophages and have implications for the development of targeted therapies to eliminate persistent infections or reduce the negative effects related with chronic inflammatory diseases associated with hRSV infection.

"All for One and One for All": The Secreted Heat Shock Protein gp96-Ig Based Vaccines

It has been 50 years since Peter Charles Doherty and Rolf M Zinkernagel proposed the principle of "simultaneous dual recognition", according to which adaptive immune cells recognized "self" and "non-self" simultaneously to establish immunological efficacy. These two scientists shared the 1996 Nobel Prize in Physiology or Medicine for this discovery. Their basic immunological principle became the foundation for the development of numerous vaccine approaches against infectious diseases and tumors, including promising strategies grounded on the use of recombinant gp96-Ig developed by our lab over the last two decades. In this review, we will highlight three major principles of the gp96-Ig vaccine strategy: (1) presentation of pathogenic antigens to T cells (specificity); (2) activation of innate immune responses (adjuvanticity); (3) priming of T cells to home to the epithelial compartments (mucosal immunity). In summary, we provide a paradigm for a vaccine approach that can be rapidly engineered and customized for any future pathogens that require induction of effective tissue-resident memory responses in epithelial tissues.

Innate Immune Pathways in Atherosclerosis-From Signaling to Long-Term Epigenetic Reprogramming

Innate immune pathways play a crucial role in the development of atherosclerosis, from sensing initial danger signals to the long-term reprogramming of immune cells. Despite the success of lipid-lowering therapy, anti-hypertensive medications, and other measures in reducing complications associated with atherosclerosis, cardiovascular disease (CVD) remains the leading cause of death worldwide. Consequently, there is an urgent need to devise novel preventive and therapeutic strategies to alleviate the global burden of CVD. Extensive experimental research and epidemiological studies have demonstrated the dominant role of innate immune mechanisms in the progression of atherosclerosis. Recently, landmark trials including CANTOS, COLCOT, and LoDoCo2 have provided solid evidence demonstrating that targeting innate immune pathways can effectively reduce the risk of CVD. These groundbreaking trials mark a significant paradigm shift in the field and open new avenues for atheroprotective treatments. It is therefore crucial to comprehend the intricate interplay between innate immune pathways and atherosclerosis for the development of targeted therapeutic interventions. Additionally, unraveling the mechanisms underlying long-term reprogramming may offer novel strategies to reverse the pro-inflammatory phenotype of immune cells and restore immune homeostasis in atherosclerosis. In this review, we present an overview of the innate immune pathways implicated in atherosclerosis, with a specific focus on the signaling pathways driving chronic inflammation in atherosclerosis and the long-term reprogramming of immune cells within atherosclerotic plaque. Elucidating the molecular mechanisms governing these processes presents exciting opportunities for the development of a new class of immunotherapeutic approaches aimed at reducing inflammation and promoting plaque stability. By addressing these aspects, we can potentially revolutionize the management of atherosclerosis and its associated cardiovascular complications.

Immunogenic cell death: The cornerstone of oncolytic viro-immunotherapy

According to the World Health Organization, cancer is one of the leading global health concerns, causing nearly 10 million deaths in 2020. While classical chemotherapeutics produce strong cytotoxicity on cancer cells, they carry limitations of drug resistance and off-target effects and sometimes fail to elicit adequate antitumor protection against tumor relapse. Additionally, most cancer cells have developed various ways to escape immune surveillance. Nevertheless, novel anticancer strategies such as oncolytic viro-immunotherapy can trigger immunogenic cell death (ICD), which can quickly grasp the attention of the host defense machinery, resulting in an ensuing antitumor immune response. Specifically, oncolytic viruses (OVs) can infect and destroy targeted cancer cells and stimulate the immune system by exposing pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) to promote inflammatory reactions, and concomitantly prime and induce antitumor immunity by the release of neoantigens from the damaged cancer cells. Thus, OVs can serve as a novel system to sensitize tumor cells for promising immunotherapies. This review discusses the concept of ICD in cancer, centralizing ICD-associated danger signals and their consequence in antitumor responses and ICD induced by OVs. We also shed light on the potential strategies to enhance the immunogenicity of OVs, including the use of genetically modified OVs and their combination with ICD-enhancing agents, which are helpful as forthcoming anticancer regimens.

Molecular Chaperone Receptors: An Update

Extracellular heat shock proteins (HSP) play important roles in cell signaling and immunity. Many of these effects are mediated by surface receptors expressed on a wide range of cell types, including immune cells. We have investigated the nature of such proteins by cloning candidate receptors into cells (CHO-K1) with the rare property of being null for HSP binding. Using this approach, we have discovered that mammalian and eukaryotic Hsp70 binds avidly to at least three classes of receptor including: (1) c-type lectin receptors (CLR), (2) scavenger receptors (SR) and (3) lectins. However, the structural nature of the receptor-ligand interactions is not currently clear. Hsp70 can bind to LOX-1 (a member of both the CLR and SR), with the c-type lectin binding domain (CTLD), to the SR family members SREC-I and FEEL-1/CLEVER-1/STABILIN-1, which by contrast have arrays of EGF-like repeats in their extracellular domains as well. In this chapter, we will discuss: (1) methods for the discovery of HSP receptors, (2) approaches to the study of individual receptors in cells that contain multiple such receptors and (3) methods for investigating HSP receptor function in vivo.

Biological causes of immunogenic cancer cell death (ICD) and anti-tumor therapy; Combination of Oncolytic virus-based immunotherapy and CAR T-cell therapy for ICD induction

Chimeric antigen receptor (CAR) T-cell therapy is a promising and rapidly expanding therapeutic option for a wide range of human malignancies. Despite the ongoing progress of CAR T-cell therapy in hematologic malignancies, the application of this therapeutic strategy in solid tumors has encountered several challenges due to antigen heterogeneity, suboptimal CAR T-cell trafficking, and the immunosuppressive features of the tumor microenvironment (TME). Oncolytic virotherapy is a novel cancer therapy that employs competent or genetically modified oncolytic viruses (OVs) to preferentially proliferate in tumor cells. OVs in combination with CAR T-cells are promising candidates for overcoming the current drawbacks of CAR T-cell application in tumors through triggering immunogenic cell death (ICD) in cancer cells. ICD is a type of cellular death in which danger-associated molecular patterns (DAMPs) and tumor-specific antigens are released, leading to the stimulation of potent anti-cancer immunity. In the present review, we discuss the biological causes of ICD, different types of ICD, and the synergistic combination of OVs and CAR T-cells to reach potent tumor-specific immunity.

Scavenger receptor class F member 2 (SCARF2) as a novel therapeutic target in glioblastoma

Scavenger receptor class F member 2 (SCARF2) is expressed by endothelial cells with very large cytoplasmic domains and is the second isotype, also known as scavenger receptor expressed by endothelial cells 2 (SREC-2). SREC-1 plays an important role in the binding and endocytosis of various endogenous and exogenous ligands. Many studies have been carried out on modified low-density lipoprotein internalization activity, but there have been few studies on SCARF2. Higher expression of SCARF2 has been found in glioblastoma (GBM) than normal brain tissue. Through analysis of The Cancer Genome Atlas database, it was confirmed that SCARF2 is widely expressed in GBM, and increased SCARF2 expression correlated with a poor prognosis in patients with glioma. The results of this study showed that the expression of SCARF2 is increased in GBM cell lines and patients, suggesting that SCARF2 may be a potential diagnostic marker and therapeutic molecule for cancers including glioma.

Current strategies in engaging oncolytic viruses with antitumor immunity

Oncolytic virotherapy has produced promising yet limited results in preclinical and clinical studies. Besides direct oncolytic activity, a significant therapeutic mechanism of oncolytic virotherapy is the induction of tumor-specific immunity. Consequently, the efficacy of oncolytic viruses can be improved by the insertion of immune stimulator genes and rational combinatorial therapy with other immunotherapies. This article reviews recent efforts on arming oncolytic viruses with a variety of immune stimulator molecules, immune cell engagers, and other immune potentiating molecules. We outline what is known about the mechanisms of action and the corresponding results. The review also discusses recent preclinical and clinical studies of combining oncolytic virotherapy with immune-checkpoint inhibitors and the role of oncolytic virotherapy in changing the tumor microenvironment.

The Role of SREC-Ⅰ in Innate Immunity to Aspergillus fumigatus Keratitis

Purpose

To determine the role of scavenger receptor expressed by endothelial cell-1 (SREC-Ⅰ) in vitro and in a mouse model of Aspergillus fumigatus keratitis.

Methods

SREC-Ⅰ mRNA and protein expression were tested in both normal and A fumigatus stimulated human corneal epithelial cells (HCECs). Immunofluorescence was used to detect SREC-Ⅰ expression in human corneas with or without A fumigatus infection. HCECs were incubated with SREC-Ⅰ small interfering RNA, then the mRNA levels of LOX-1, IL-1β, and TNF-α were detected after A fumigatus stimulation. A mouse fungal keratitis (FK) model was established and SREC-Ⅰ mRNA and protein expression were detected by RT-PCR, Western blot and immunofluorescence. The severity of FK was evaluated by clinical score. CLCX1, LOX-1, IL-1β, and TNF-α mRNA expression levels were tested before and after anti-SREC-Ⅰ treatment.

Results

SREC-Ⅰ expressed in normal and A fumigatus treated HCECs and human corneal epithelium. In vitro experiment showed that SREC-Ⅰ mRNA and protein levels were significantly increased after A fumigatus stimulation. SREC-Ⅰ small interfering RNA treatment inhibited the expressions of LOX-1, IL-1β, and TNF-α in HCECs. The expressions of CLCX1, LOX-1, IL-1β, and TNF-α were elevated in mice with A fumigatus keratitis, which could be decreased by SREC-Ⅰ-neutralizing antibody treatment.

Conclusions

SREC-Ⅰ is a key mediator in inflammatory response induced by A fumigatus keratitis. SREC-Ⅰ blockade could be a potential therapeutic approach for FK.

CD36 Ectodomain Detects Apoptosis in Mammalian Cells

The cells that undergo apoptosis show phosphatidylserine (PS) on the cell membrane. The fluorescently labeled hCD36_ecto is staining and detecting apoptotic cells in a flow-based assay with several advantages over Annexin V. The human CD36 ectodomain (hCD36_ecto) is stable for a range of temperatures and experimental conditions and doesn't require Ca²⁺ for detecting apoptosis and specific towards PS compared to other lipids. The blocking with unlabeled hCD36_ecto reduces the staining of Annexin V-FITC for apoptotic cells, whereas R63A does not affect the binding of Annexin V- FITC to apoptotic cells. It indicates the role of CD36-PS interaction in detecting apoptotic cells. Dual-staining with hCD36_ecto-FITC/PI is universally detecting apoptosis in different nucleated cells or eryptosis in non-nucleated RBCs. Hence, our study highlights the utility of CD36 as a probe to detect apoptosis in mammalian cells. It might be a robust, economical reagent for the scientific community to facilitate their research.

Heat Shock Proteins 90 kDa: Immunomodulators and Adjuvants in Vaccine Design Against Infectious Diseases

Heat shock proteins 90 kDa (Hsp90s) were originally identified as stress-responsive proteins and described to participate in several homeostatic processes. Additionally, extracellular Hsp90s have the ability to bind to surface receptors and activate cellular functions related to immune response (cytokine secretion, cell maturation, and antigen presentation), making them very attractive to be studied as immunomodulators. In this context, Hsp90s are proposed as new adjuvants in the design of novel vaccine formulations that require the induction of a cell-mediated immune response to prevent infectious diseases. In this review, we summarized the adjuvant properties of Hsp90s when they are either alone, complexed, or fused to a peptide to add light to the knowledge of Hsp90s as carriers and adjuvants in the design of vaccines against infectious diseases. Besides, we also discuss the mechanisms by which Hsp90s activate and modulate professional antigen-presenting cells.

Targeting Tumor-Associated Macrophages in the Pediatric Sarcoma Tumor Microenvironment

For many pediatric sarcoma patients, multi-modal therapy including chemotherapy, radiation, and surgery is sufficient to cure their disease. However, event-free and overall survival rates for patients with more advanced disease are grim, necessitating the development of novel therapeutic approaches. Within many pediatric sarcomas, the normal immune response, including recognition and destruction of cancer cells, is lost due to the highly immune suppressive tumor microenvironment (TME). In this setting, tumor cells evade immune detection and capitalize on the immune suppressed microenvironment, leading to unchecked proliferation and metastasis. Recent preclinical and clinical approaches are aimed at understanding this immune suppressive microenvironment and employing cancer immunotherapy in an attempt to overcome this, by renewing the ability of the immune system to recognize and destroy cancer cells. While there are several factors that drive the attenuation of immune responses in the sarcoma TME, one of the most remarkable are tumor associated macrophage (TAMs). TAMs suppress immune cytolytic function, promote tumor growth and metastases, and are generally associated with a poor prognosis in most pediatric sarcoma subtypes. In this review, we summarize the mechanisms underlying TAM-facilitated immune evasion and tumorigenesis and discuss the potential therapeutic application of TAM-focused drugs in the treatment of pediatric sarcomas.

Fibroblast-Derived STC-1 Modulates Tumor-Associated Macrophages and Lung Adenocarcinoma Development

The tumor microenvironment (TME) consists of different cell types, including tumor-associated macrophages (TAMs) and tumor-associated fibroblasts (TAFs). How these cells interact and contribute to lung carcinogenesis remains elusive. Using G12DKRAS- and V600EBRAF-driven mouse lung models, we identify the pleiotropic glycoprotein stanniocalcin-1 (STC1) as a regulator of TAM-TAF interactions. STC1 is secreted by TAFs and suppresses TAM differentiation, at least in part, by sequestering the binding of GRP94, an autocrine macrophage-differentiation-inducing factor, to its cognate scavenger receptors. The accumulation of mature TAMs in the Stc1-deficient lung leads to enhanced secretion of TGF-β1 and, thus, TAF accumulation in the TME. Consistent with the mouse data, in human lung adenocarcinoma, STC1 expression is restricted to myofibroblasts, and a significant increase of naive macrophages is detected in STC1-high compared with STC1-low cases. This work increases our understanding of lung adenocarcinoma development and suggests new approaches for therapeutic targeting of the TME.

Molecular and Cellular Interactions of Scavenger Receptor SR-F1 With Complement C1q Provide Insights Into Its Role in the Clearance of Apoptotic Cells

The scavenger receptor SR-F1 binds to and mediates the internalization of a wide range of ligands, and is involved in several immunological processes. We produced recombinant SR-F1 ectodomain and fragments deleted from the last 2 or 5 C-terminal epidermal growth factor-like modules and investigated their role in the binding of acetylated low density lipoprotein (AcLDL), complement C1q, and calreticulin (CRT). C1q measured affinity was in the 100 nM range and C1q interaction occurs via its collagen-like region. We identified two different binding regions on SR-F1: the N-terminal moiety interacts with C1q and CRT whereas the C-terminal moiety binds AcLDL. The role of SR-F1 N-linked glycans was also tested by mutating each of the three glycosylated asparagines. The three mutants retained binding activities for both AcLDL and C1q. A stable THP-1 cell line overexpressing SR-F1 was generated and C1q was shown to bind more strongly to the surface of SR-F1 overexpressing macrophages, with C1q/SR-F1 colocalization observed in some membrane areas. We also observed a higher level of CRT internalization for THP-1 SR-F1 cells. Increasing SR-F1 negatively modulated the uptake of apoptotic cells. Indeed, THP-1 cells overexpressing SR-F1 displayed a lower phagocytic capacity as compared with mock-transfected cells, which could be partially restored by addition of C1q in the extracellular milieu. Our data shed some light on the role of SR-F1 in efferocytosis, through its capacity to bind C1q and CRT, two proteins involved in this process.

In Vitro Employment of Recombinant Taenia solium Calreticulin as a Novel Strategy Against Breast and Ovarian Cancer Stem-like Cells

BACKGROUND AND AIMS

Calreticulin is a chaperone and master regulator of intracellular calcium homeostasis. Several additional functions have been discovered. Human and parasite calreticulin have been shown to suppress mammary tumor growth in vivo. Here, we explored the capacity of recombinant Taenia solium calreticulin (rTsCRT) to modulate cancer cell growth in vitro.

METHODS

We used different concentrations of rTsCRT to treat cancer cell lines and analyzed viability and colony formation capacity. We also tested the combination of the IC₂₀ or IC₅₀ doses of rTsCRT and of the chemotherapeutic drug 5-fluorouracil on MCF7 and SKOV3 cell lines. As a control, the non-tumorigenic cell line MCF10-A was employed. The effect of the drug combinations was also assessed in cancer stem-like cells. Additionally, scavenger receptor ligands were employed to identify the role of this receptor in the rTsCRT anti-tumoral effect.

RESULTS

rTsCRT has a dose-dependent in vitro anti-tumoral effect, being SKOV3 the most sensitive cell line followed by MCF7. When rTsCRT/5-fluorouracil were used, MCF7 and SKOV3 showed a 60% reduction in cell viability; colony formation capacity was also diminished. Treatment of cancer stem-like cells from MCF7 showed a higher reduction in cell viability, while those from SKOV3 were more sensitive to colony disaggregation. Finally, pharmacological inhibition of the scavenger receptor, abrogated the reduction in viability induced by rTsCRT in both the parental and stem-like cells.

CONCLUSION

Our data suggest that rTsCRT alone or in combination with 5-fluorouracil inhibits the growth of breast and ovarian cancer cell lines through its interaction with scavenger receptors.

Voices from the dead: The complex vocabulary and intricate grammar of dead cells

Of the roughly one million cells per second dying throughout the body, the vast majority dies by apoptosis, the predominant form of regulated cell death in higher organisms. Long regarded as mere waste, apoptotic cells are now recognized as playing a prominent and active role in homeostatic maintenance, especially resolution of inflammation, and in the sculpting of tissues during development. The activities associated with apoptotic cells are continually expanding, with more recent studies demonstrating their ability to modulate such vital functions as proliferation, survival, differentiation, metabolism, migration, and angiogenesis. In each case, the role of apoptotic cells is active, exerting their effects via new activities acquired during the apoptotic program. Moreover, the capacity to recognize and respond to apoptotic cells is not limited to professional phagocytes. Most, if not all, cells receive and integrate an array of signals from cells dying in their vicinity. These signals comprise a form of biochemical communication. As reviewed in this chapter, this communication is remarkably sophisticated; each of its three critical steps-encoding, transmission, and decoding of the apoptotic cell's "message"-is endowed with exquisite robustness. Together, the abundance and intricacy of the variables at each step comprise the vocabulary and grammar of the language by which dead cells achieve their post-mortem voice. The combinatorial complexity of the resulting communication network permits dying cells, through the signals they emit and the responses those signals elicit, to partake of an expanded role in homeostasis, acting as both sentinels of environmental change and agents of adaptation.

Critical Interactions between Immunogenic Cancer Cell Death, Oncolytic Viruses, and the Immune System Define the Rational Design of Combination Immunotherapies

Oncolytic viruses (OVs) are multimodal cancer therapeutics, with one of their dominant mechanisms being in situ vaccination. There is a growing consensus that optimal cancer therapies should generate robust tumor-specific immune responses. Immunogenic cell death (ICD) is a paradigm of cellular demise culminating in the spatiotemporal release of danger-associated molecular patterns that induce potent anticancer immunity. Alongside traditional ICD inducers like anthracycline chemotherapeutics and radiation, OVs have emerged as novel members of this class of therapeutics. OVs replicate in cancers and release tumor Ags, which are perceived as dangerous because of simultaneous expression of pathogen-associated molecular patterns that activate APCs. Therefore, OVs provide the target Ags and danger signals required to induce adaptive immune responses. This review discusses why OVs are attractive candidates for generating ICD, biological barriers limiting their success in the clinic, and groundbreaking strategies to potentiate ICD and antitumor immunity with rationally designed OV-based combination therapies.

Modulation of the Tumor Microenvironment by CXCR4 Antagonist-Armed Viral Oncotherapy Enhances the Antitumor Efficacy of Dendritic Cell Vaccines against Neuroblastoma in Syngeneic Mice

The induction of antitumor immune responses in tumor-bearing hosts depends on efficient uptake and processing of native or modified tumors/self-antigens by dendritic cells (DCs) to activate immune effector cells, as well as the extent of the immunosuppressive network in the tumor microenvironment (TME). Because the C-X-C motif chemokine receptor 4 (CXCR4) for the C-X-C motif chemokine 12 (CXCL12) is involved in signaling interactions between tumor cells and their TME, we used oncolytic virotherapy with a CXCR4 antagonist to investigate whether targeting of the CXCL12/CXCR4 signaling axis in murine neuroblastoma cells (NXS2)-bearing syngeneic mice affects the efficacy of bone marrow (BM)-derived DCs loaded with autologous tumor cells treated with doxorubicin for induction of immunogenic cell death. Here, we show that CXCR4 antagonist expression from an oncolytic vaccinia virus delivered intravenously to mice with neuroblastoma tumors augmented efficacy of the DC vaccines compared to treatments mediated by a soluble CXCR4 antagonist or oncolysis alone. This study is the first demonstration that modulating the tumor microenvironment by an armed oncolytic virus could have a significant impact on the efficacy of DC vaccines, leading to the generation of effective protection against neuroblastoma challenge.

SCARF1: a multifaceted, yet largely understudied, scavenger receptor

BACKGROUND

As is a prerequisite of belonging to the scavenger receptor super family, SCARF1 (scavenger receptor class F, member 1) is known to play a key role in the binding and endocytosis of a wide range of endogenous and exogenous ligands.

FINDINGS

Unlike most scavenger receptors, SCARF1 is an essential protein, as SCARF1-deficient mice exhibit a severe resting phenotype in which they develop systemic lupus erythematosus (SLE)-like disease, thus highlighting the importance of SCARF1-mediated clearance of apoptotic host cells in homeostasis. In addition, a number of other roles in homeostasis and disease pathology have also been suggested, including roles in both innate and adaptive immunity; however, the majority of these studies have utilised transfected cell lines engineered to ectopically express SCARF1 and very few have utilised in vivo or ex vivo approaches.

CONCLUSION

This review summarises our current knowledge on SCARF1 biology and reflects on future directions for research on this multifaceted, yet largely understudied, scavenger receptor.

Molecular Chaperone Receptors

Extracellular heat shock proteins (HSP) play important roles in cell signaling and immunity. Many of these effects are mediated by surface receptors expressed on a wide range of cell types. We have investigated the nature of such proteins by cloning candidate receptors into cells (CHO-K1) with the rare property of being null for HSP binding. Using this approach we have discovered that Hsp70 binds avidly to at least two classes of receptors including: (1) c-type lectin receptors (CLR) and (2) scavenger receptors (SR). However, the structural nature of the receptor-ligand interactions is not clear at this time. Hsp70 can bind to LOX-1 (a member of both the CLR and SR), with the c-type lectin binding domain (CTLD) as well as the SR family members SREC-I and FEEL-1/CLEVER-1/STABILIN-1, which by contrast have arrays of EGF-like repeats in their extracellular domains. In this chapter we will discuss: (1) methods for discovery of HSP receptors, (2) approaches to the study of individual receptors in cells that contain multiple such receptors, and (3) methods for investigating HSP receptor function in vivo.

Calreticulin Release at an Early Stage of Death Modulates the Clearance by Macrophages of Apoptotic Cells

Calreticulin (CRT) is a well-known “eat-me” signal harbored by dying cells participating in their recognition by phagocytes. CRT is also recognized to deeply impact the immune response to altered self-cells. In this study, we focus on the role of the newly exposed CRT following cell death induction. We show that if CRT increases at the outer face of the plasma membrane and is well recognized by C1q even when phosphatidylserine is not yet detected, CRT is also released in the surrounding milieu and is able to interact with phagocytes. We observed that exogenous CRT is endocytosed by THP1 macrophages through macropinocytosis and that internalization is associated with a particular phenotype characterized by an increase of cell spreading and migration, an upregulation of CD14, an increase of interleukin-8 release, and a decrease of early apoptotic cell uptake. Importantly, CRT-induced pro-inflammatory phenotype was confirmed on human monocytes-derived macrophages by the overexpression of CD40 and CD274, and we found that monocyte-derived macrophages exposed to CRT display a peculiar polarization notably associated with a downregulation of the histocompatibility complex of class II molecules hampering its description through the classical M1/M2 dichotomy. Altogether our results highlight the role of soluble CRT with strong possible consequences on the macrophage-mediated immune response to dying cell.

C1q: A fresh look upon an old molecule

Originally discovered as part of C1, the initiation component of the classical complement pathway, it is now appreciated that C1q regulates a variety of cellular processes independent of complement activation. C1q is a complex glycoprotein assembled from 18 polypeptide chains, with a C-terminal globular head region that mediates recognition of diverse molecular structures, and an N-terminal collagen-like tail that mediates immune effector mechanisms. C1q mediates a variety of immunoregulatory functions considered important in the prevention of autoimmunity such as the enhancement of phagocytosis, regulation of cytokine production by antigen presenting cells, and subsequent alteration in T-lymphocyte maturation. Furthermore, recent advances indicate additional roles for C1q in diverse physiologic and pathologic processes including pregnancy, tissue repair, and cancer. Finally, C1q is emerging as a critical component of neuronal network refinement and homeostatic regulation within the central nervous system. This review summarizes the classical functions of C1q and reviews novel discoveries within the field.

Biotechnology approaches to produce potent, self-adjuvanting antigen-adjuvant fusion protein subunit vaccines

Traditional vaccination approaches (e.g. live attenuated or killed microorganisms) are among the most effective means to prevent the spread of infectious diseases. These approaches, nevertheless, have failed to yield successful vaccines against many important pathogens. To overcome this problem, methods have been developed to identify microbial components, against which protective immune responses can be elicited. Subunit antigens identified by these approaches enable the production of defined vaccines, with improved safety profiles. However, they are generally poorly immunogenic, necessitating their administration with potent immunostimulatory adjuvants. Since few safe and effective adjuvants are currently used in vaccines approved for human use, with those available displaying poor potency, or an inability to stimulate the types of immune responses required for vaccines against specific diseases (e.g. cytotoxic lymphocytes (CTLs) to treat cancers), the development of new vaccines will be aided by the availability of characterized platforms of new adjuvants, improving our capacity to rationally select adjuvants for different applications. One such approach, involves the addition of microbial components (pathogen-associated molecular patterns; PAMPs), that can stimulate strong immune responses, into subunit vaccine formulations. The conjugation of PAMPs to subunit antigens provides a means to greatly increase vaccine potency, by targeting immunostimulation and antigen to the same antigen presenting cell. Thus, methods that enable the efficient, and inexpensive production of antigen-adjuvant fusions represent an exciting mean to improve immunity towards subunit antigens. Herein we review four protein-based adjuvants (flagellin, bacterial lipoproteins, the extra domain A of fibronectin (EDA), and heat shock proteins (Hsps)), which can be genetically fused to antigens to enable recombinant production of antigen-adjuvant fusion proteins, with a focus on their mechanisms of action, structural or sequence requirements for activity, sequence modifications to enhance their activity or simplify production, adverse effects, and examples of vaccines in preclinical or human clinical trials.

Apoptotic cell recognition receptors and scavenger receptors

Phosphatidylserine recognition receptors are a highly diverse set of receptors grouped by their ability to recognize the 'eat-me' signal phosphatidylserine on apoptotic cells. Most of the phosphatidylserine recognition receptors dampen inflammation by inducing the production of anti-inflammatory mediators during the phagocytosis of apoptotic corpses. However, many phosphatidylserine receptors are also capable of recognizing other ligands, with some receptors being categorized as scavenger receptors. It is now appreciated that these receptors can elicit different downstream events for particular ligands. Therefore, how phosphatidylserine recognition receptors mediate specific signals during recognition of apoptotic cells versus other ligands, and how this might help regulate the inflammatory state of a tissue is an important question that is not fully understood. Here, we revisit the work on signaling downstream of the phosphatidylserine recognition receptor BAI1, and evaluate how these and other signaling modules mediate signaling downstream from other receptors, including Stabilin-2, MerTK, and αvβ5. We also propose the concept that phosphatidylserine recognition receptors could be viewed as a subset of scavenger receptors that are capable of eliciting anti-inflammatory responses to apoptotic cells.

Human CD1c(+) DCs are critical cellular mediators of immune responses induced by immunogenic cell death

Chemotherapeutics, including the platinum compounds oxaliplatin (OXP) and cisplatin (CDDP), are standard care of treatment for cancer. Although chemotherapy has long been considered immunosuppressive, evidence now suggests that certain cytotoxic agents can efficiently stimulate antitumor responses, through the induction of a form of apoptosis, called immunogenic cell death (ICD). ICD is characterized by exposure of calreticulin and heat shock proteins (HSPs), secretion of ATP and release of high-mobility group box 1 (HMGB1). Proper activation of the immune system relies on the integration of these signals by dendritic cells (DCs). Studies on the crucial role of DCs, in the context of ICD, have been performed using mouse models or human in vitro-generated monocyte-derived DCs (moDCs), which do not fully recapitulate the in vivo situation.

Here, we explore the effect of platinum-induced ICD on phenotype and function of human blood circulating DCs. Tumor cells were treated with OXP or CDDP and induction of ICD was investigated. We show that both platinum drugs triggered translocation of calreticulin and HSP70, as well as the release of ATP and HMGB1. Platinum treatment increased phagocytosis of tumor fragments by human blood DCs and enhanced phenotypic maturation of blood myeloid and plasmacytoid DCs. Moreover, upon interaction with platinum-treated tumor cells, CD1c⁺ DCs efficiently stimulated allogeneic proliferation of T lymphocytes. Together, our observations indicate that platinum-treated tumor cells may exert an active stimulatory effect on human blood DCs. In particular, these data suggest that CD1c⁺ DCs are critical mediators of immune responses induced by ICD.

Extracellular HSPs: The Complicated Roles of Extracellular HSPs in Immunity

Extracellular heat-shock proteins (HSPs) interact with the immune system in a very complex manner. Many such HSPs exert powerful effects on the immune response, playing both stimulatory and regulatory roles. However, the influence of the HSPs on immunity appears to be positive or negative in nature – rarely neutral. Thus, the HSPs can act as dominant antigens and can comprise key components of antitumor vaccines. They can also function as powerful immunoregulatory agents and, as such, are employed to treat inflammatory diseases or to extend the lifespan of tissue transplants. Small modifications in the cellular milieu have been shown to flip the allegiances of HSPs from immunoregulatory agents toward a potent inflammatory alignment. These mutable properties of HSPs may be related to the ability of these proteins to interact with multiple receptors often with mutually confounding properties in immune cells. Therefore, understanding the complex immune properties of HSPs may help us to harness their potential in treatment of a range of conditions.

Unfolding the Role of Large Heat Shock Proteins: New Insights and Therapeutic Implications

Heat shock proteins (HSPs) of eukaryotes are evolutionarily conserved molecules present in all the major intracellular organelles. They mainly function as molecular chaperones and participate in maintenance of protein homeostasis in physiological state and under stressful conditions. Despite their relative abundance, the large HSPs, i.e., Hsp110 and glucose-regulated protein 170 (Grp170), have received less attention compared to other conventional HSPs. These proteins are distantly related to the Hsp70 and belong to Hsp70 superfamily. Increased sizes of Hsp110 and Grp170, due to the presence of a loop structure, result in their exceptional capability in binding to polypeptide substrates or non-protein ligands, such as pathogen-associated molecules. These interactions that occur in the extracellular environment during tissue injury or microbial infection may lead to amplification of an immune response engaging both innate and adaptive immune components. Here, we review the current advances in understanding these large HSPs as molecular chaperones in proteostasis control and immune modulation as well as their therapeutic implications in treatment of cancer and neurodegeneration. Given their unique immunoregulatory activities, we also discuss the emerging evidence of their potential involvement in inflammatory and immune-related diseases.

The SREC-I and SREC-II associated with epidermal growth factor in scavenger receptor family are the potential regulative transmembrane receptors in Larimichthys crocea

In innate immunity, the regulation of the immunologic gene expression plays a vital role in defense against pathogenic threat. The class F scavenger receptors (SCARFs), a kind of crucial immunologic type I transmembrane receptors, mainly involve in the signal transmission and eliminating pathogens in host immune system. In this study, the SREC-I and SREC-II of SCARFs in Larimichthys crocea (designated as LycSREC1 and LycSREC2 respectively) were first identified, the potential genetic locus relationships with other species were depicted and the features of gene expression after Vibrio alginolyticus stimulation were tested. The results demonstrated that the complete ORF sequences of two candidates were 3024 bp and 2832 bp (KM884873 and KM884874) respectively including some important domains and motifs, such as EGF/EGF-like domains, TRAF2-binding consensus motif, generic motif and atipical motif. The gene location maps and genetic locus interpreted that the DNA sequences of LycSREC1 and LycSREC2 were 7603 bp and 4883 bp, and some locus had changed compared with human being, but three more crucial genetic locus were conservative among ten species. Furthermore, quantitative real-time PCR (qRT-PCR) analysis indicated that the highest mRNA expression of LycSREC1 and LycSREC2 were both in liver among eight detected tissues, and their expression were up-regulated by V. alginolyticus stimulation. All these findings would contribute to better understanding the biologic function of SCARFs in defending against pathogenic bacteria challenge and further exploring the innate immune of sciaenidae fish.

Scavenger Receptors: Emerging Roles in Cancer Biology and Immunology

Scavenger receptors constitute a large family of evolutionally conserved protein molecules that are structurally and functionally diverse. Although scavenger receptors were originally identified based on their capacity to scavenge modified lipoproteins, these molecules have been shown to recognize and bind to a broad spectrum of ligands, including modified and unmodified host-derived molecules or microbial components. As a major subset of innate pattern recognition receptors, scavenger receptors are mainly expressed on myeloid cells and function in a wide range of biological processes, such as endocytosis, adhesion, lipid transport, antigen presentation, and pathogen clearance. In addition to playing a crucial role in maintenance of host homeostasis, scavenger receptors have been implicated in the pathogenesis of a number of diseases, e.g., atherosclerosis, neurodegeneration, or metabolic disorders. Emerging evidence has begun to reveal these receptor molecules as important regulators of tumor behavior and host immune responses to cancer. This review summarizes our current understanding on the newly identified, distinct functions of scavenger receptors in cancer biology and immunology. The potential of scavenger receptors as diagnostic biomarkers and novel targets for therapeutic interventions to treat malignancies is also highlighted.

Scavenger receptor SREC-I mediated entry of TLR4 into lipid microdomains and triggered inflammatory cytokine release in RAW 264.7 cells upon LPS activation

Scavenger receptor associated with endothelial cells I (SREC-I) was shown to be expressed in immune cells and to play a role in the endocytosis of peptides and antigen presentation. As our previous studies indicated that SREC-I required intact Toll-like receptor 4 (TLR4) expression for its functions in tumor immunity, we examined potential interactions between these two receptors. We have shown here that SREC-I became associated with TLR4 on binding bacterial lipopolysaccharides (LPS) in RAW 264.7 and HEK 293 cells overexpressing these two receptors. The receptors then became internalized together in intracellular endosomes. SREC-I promoted TLR4-induced signal transduction through the NF-kB and MAP kinase pathways, leading to enhanced inflammatory cytokine release. Activation of inflammatory signaling through SREC-I/TLR4 complexes appeared to involve recruitment of the receptors into detergent-insoluble, cholesterol-rich lipid microdomains that contained the small GTPase Cdc42 and the non-receptor tyrosine kinase c-src. Under conditions of SREC-I activation by LPS, TLR4 activity required Cdc42 as well as cholesterol and actin polymerization for signaling through NF-kB and MAP kinase pathways in RAW 264.7 cells. SREC-I appeared to respond differently to another ligand, the molecular chaperone Hsp90 that, while triggering SREC-I-TLR4 binding caused only faint activation of the NF-kB pathway. Our experiments therefore indicated that SREC-I could bind LPS and might be involved in innate inflammatory immune responses to extracellular danger signals in RAW 264.7 cells or bone marrow-derived macrophages.

Emerging roles for scavenger receptor SREC-I in immunity

SREC-I is a class F scavenger receptor with key role in the immune response, particularly in antigen presenting cell (APC) such as macrophages and dendritic cells (DC). This receptor is able to mediate engulfment of dead cells as well as endocytosis of heat shock protein (HSP)-antigen complexes. SREC-I could thus potentially mediate the tolerizing influence of apoptotic cells or the immunostimulatory effects of HSP-peptide complexes, depending on context. This receptor was able to mediate presentation of external antigens, bound to HSPs through both the class II pathway as well as cross presentation via MHC class I complexes. In addition to its recently established role in adaptive immunity, emerging studies are indicating a broad role in innate immunity and regulation of cell signaling through Toll Like Receptors (TLR). SREC-I may thus play a key role in APC function by coordinating immune responses to internal and external antigens in APC.

A nasal epithelial receptor for Staphylococcus aureus WTA governs adhesion to epithelial cells and modulates nasal colonization

Nasal colonization is a major risk factor for S. aureus infections. The mechanisms responsible for colonization are still not well understood and involve several factors on the host and the bacterial side. One key factor is the cell wall teichoic acid (WTA) of S. aureus, which governs direct interactions with nasal epithelial surfaces. We report here the first receptor for the cell wall glycopolymer WTA on nasal epithelial cells. In several assay systems this type F-scavenger receptor, termed SREC-I, bound WTA in a charge dependent manner and mediated adhesion to nasal epithelial cells in vitro. The impact of WTA and SREC-I interaction on epithelial adhesion was especially pronounced under shear stress, which resembles the conditions found in the nasal cavity. Most importantly, we demonstrate here a key role of the WTA-receptor interaction in a cotton rat model of nasal colonization. When we inhibited WTA mediated adhesion with a SREC-I antibody, nasal colonization in the animal model was strongly reduced at the early onset of colonization. More importantly, colonization stayed low over an extended period of 6 days. Therefore we propose targeting of this glycopolymer-receptor interaction as a novel strategy to prevent or control S. aureus nasal colonization.

About 20% of the human population is colonized by Staphylococcus aureus. The reservoir of S. aureus is mainly the human nose. Usually, colonization does not lead to infection and is therefore without symptoms. However, when hospitalized patients exhibit a suppressed immune system, they are at risk of getting infected by their own nasal S. aureus strain. Therefore, it is important to understand the events and mechanisms underlying colonization. Until now S. aureus nasal colonization is only partially understood. One bacterial key factor is a sugar polymer of S. aureus, termed cell wall teichoic acid (WTA), which is involved in S. aureus adhesion to cellular surfaces in the inner part of the nasal cavity. We show here that a receptor-protein, which is expressed on such cells, binds WTA and is thereby involved in adhesion of S. aureus to nasal cells. This mechanism has a strong impact on nasal colonization in an animal model that resembles the situation in the human nose. Most importantly, inhibition of WTA mediated adhesion strongly reduces nasal colonization in the animal model. Therefore we propose that targeting of this glycopolymer-receptor interaction could serve as a novel strategy to control S. aureus nasal colonization.

Therapeutic cancer vaccines: past, present, and future

Therapeutic vaccines represent a viable option for active immunotherapy of cancers that aim to treat late stage disease by using a patient's own immune system. The promising results from clinical trials recently led to the approval of the first therapeutic cancer vaccine by the U.S. Food and Drug Administration. This major breakthrough not only provides a new treatment modality for cancer management but also paves the way for rationally designing and optimizing future vaccines with improved anticancer efficacy. Numerous vaccine strategies are currently being evaluated both preclinically and clinically. This review discusses therapeutic cancer vaccines from diverse platforms or targets as well as the preclinical and clinical studies employing these therapeutic vaccines. We also consider tumor-induced immune suppression that hinders the potency of therapeutic vaccines, and potential strategies to counteract these mechanisms for generating more robust and durable antitumor immune responses.

Fucoidan as a marine anticancer agent in preclinical development

Fucoidan is a fucose-containing sulfated polysaccharide derived from brown seaweeds, crude extracts of which are commercially available as nutritional supplements. Recent studies have demonstrated antiproliferative, antiangiogenic, and anticancer properties of fucoidan in vitro. Accordingly, the anticancer effects of fucoidan have been shown to vary depending on its structure, while it can target multiple receptors or signaling molecules in various cell types, including tumor cells and immune cells. Low toxicity and the in vitro effects of fucoidan mentioned above make it a suitable agent for cancer prevention or treatment. However, preclinical development of natural marine products requires in vivo examination of purified compounds in animal tumor models. This review discusses the effects of systemic and local administration of fucoidan on tumor growth, angiogenesis, and immune reaction and whether in vivo and in vitro results are likely applicable to the development of fucoidan as a marine anticancer drug.

Secreted heat shock protein gp96-Ig: next-generation vaccines for cancer and infectious diseases

Over the past decade, our laboratory has developed a secreted heat shock protein (HSP), chaperone gp96, cell-based vaccine that generates effective anti-tumor and anti-infectious immunity in vivo. Gp96-peptide complexes were identified as an extremely efficient stimulator of MHC I-mediated antigen cross-presentation, generating CD8 cytotoxic T-lymphocyte responses detectable in blood, spleen, gut and reproductive tract to femto-molar concentrations of antigen. These studies provided the first evidence that cell-based gp96-Ig-secreting vaccines may serve as a potent modality to induce both systemic and mucosal immunity. This approach takes advantage of the combined adjuvant and antigen delivery capacity of gp96 for the generation of cytotoxic immunity against a wide range of antigens in both anti-vial and anti-cancer vaccination. Here, we review the vaccine design that utilizes the unique property/ability of endoplasmic HSP gp96 to bind antigenic peptides and deliver them to antigen-presenting cells.

Regulation of the expression of chaperone gp96 in macrophages and dendritic cells

The chaperone function of the ER-residing heat shock protein gp96 plays an important role in protein physiology and has additionally important immunological functions due to its peptide-binding capacity. Low amounts of gp96 stimulate immunity; high quantities induce tolerance by mechanisms not fully understood. A lack of gp96 protein in intestinal macrophages (IMACs) from Crohn`s disease (CD) patients correlates with loss of tolerance against the host gut flora, leading to chronic inflammation. Since gp96 shows dose-dependent direction of immunological reactions, we studied primary IMACs and developed cell models to understand the regulation of gp96 expression. Induction of gp96-expression was higher in in vitro differentiated dendritic cells (i.v.DCs) than in in vitro differentiated macrophages (i.v.MACs), whereas monocytes (MOs) expressed only low gp96 levels. The highest levels of expression were found in IMACs. Lipopolysaccharide (LPS), muramyl dipeptide (MDP), tumour necrosis factor (TNF), and Interleukin (IL)-4 induced gp96-expression, while IL12, IL-17, IL-23 and interferon (IFN)-γ were not effective indicating that Th1 and Th17 cells are probably not involved in the induction of gp96. Furthermore, gp96 was able to induce its own expression. The ER-stress inducer tunicamycin increased gp96-expression in a concentration- and time-dependent manner. Both ulcerative colitis (UC) and CD patients showed significantly elevated gp96 mRNA levels in intestinal biopsies which correlated positively with the degree of inflammation of the tissue. Since gp96 is highly expressed on the one hand upon stress induction as during inflammation and on the other hand possibly mediating tolerance, these results will help to understand the whether gp96 plays a role in the pathophysiology of inflammatory bowel disease (IBD).

The scavenger receptor SCARF1 mediates the clearance of apoptotic cells and prevents autoimmunity

Clearance of apoptotic cells is critical for control of tissue homeostasis however the full range of receptor(s) on phagocytes responsible for recognition of apoptotic cells remains to be identified. Here we show that dendritic cells (DCs), macrophages and endothelial cells use scavenger receptor type F family member 1 (SCARF1) to recognize and engulf apoptotic cells via C1q. Loss of SCARF1 impairs uptake of apoptotic cells. Consequently, in SCARF1-deficient mice, dying cells accumulate in tissues leading to a lupus-like disease with the spontaneous generation of autoantibodies to DNA-containing antigens, immune cell activation, dermatitis and nephritis. The discovery of SCARF1 interactions with C1q and apoptotic cells provides insights into molecular mechanisms involved in maintenance of tolerance and prevention of autoimmune disease.

High molecular weight stress proteins: Identification, cloning and utilisation in cancer immunotherapy

Although the large stress/heat shock proteins (HSPs), i.e. Hsp110 and Grp170, were identified over 30 years ago, these abundant and highly conserved molecules have received much less attention compared to other conventional HSPs. Large stress proteins act as molecular chaperones with exceptional protein-holding capability and prevent the aggregation of proteins induced by thermal stress. The chaperoning properties of Hsp110 and Grp170 are integral to the ability of these molecules to modulate immune functions and are essential for developing large chaperone complex vaccines for cancer immunotherapy. The potent anti-tumour activity of the Hsp110/Grp170-tumour protein antigen complexes demonstrated in preclinical studies has led to a phase I clinical trial through the National Cancer Institute's rapid access to intervention development (RAID) programme that is presently underway. Here we review aspects of the structure and function of these large stress proteins, their roles as molecular chaperones in the biology of cell stress, and prospects for their use in immune regulation and cancer immunotherapy. Lastly, we will discuss the recently revealed immunosuppressive activity of scavenger receptor A that binds to Hsp110 and Grp170, as well as the feasibility of targeting this receptor to promote T-cell activation and anti-tumour immunity induced by large HSP vaccines and other immunotherapies.

Adjuvanticity of a recombinant calreticulin fragment in assisting anti-β-glucan IgG responses in T cell-deficient mice

Polysaccharide-encapsulated fungi are the chief source of diseases in immunocompromised hosts such as those infected with human immunodeficiency virus or neutropenia patients. Currently available polysaccharide-protein conjugate vaccines are mainly T cell dependent and are usually ineffective in weakened immune systems. In this study, laminarin, a well-characterized β-1,3-glucan, was conjugated with a prokaryotically expressed recombinant fragment (amino acids [aa] 39 to 272) of calreticulin (rCRT/39-272), which exhibits extraordinarily potent immunogenicity and adjuvanticity in experimental animals. The resultant conjugate reserves the immunostimulatory effect of rCRT/39-272 on naïve murine B cells and is capable of eliciting anti-β-glucan IgG (mostly IgG1) responses in not only BALB/c mice but also athymic nude mice. Laminarin-CRT-induced mouse antibodies (Abs) are able to bind with Candida albicans and inhibit its growth in vitro. In addition, vaccination with laminarin-CRT partially protects mice from lethal C. albicans challenge. These results imply that rCRT/39-272 could be used as an ideal carrier or adjuvant for carbohydrate vaccines aimed at inducing or boosting IgG responses to fungal infections in immunodeficient hosts.

Immunogenic cell death: can it be exploited in PhotoDynamic Therapy for cancer?

Immunogenic Cell Death (ICD) could represent the keystone in cancer management since tumor cell death induction is crucial as well as the control of cancer cells revival after neoplastic treatment. In this context, the immune system plays a fundamental role. The concept of Damage-Associated Molecular Patterns (DAMPs) has been proposed to explain the immunogenic potential of stressed or dying/dead cells. ICD relies on DAMPs released by or exposed on dying cells. Once released, DAMPs are sensed by immune cells, in particular Dendritic Cells (DCs), acting as activators of Antigen-Presenting Cells (APCs), that in turn stimulate both innate and adaptive immunity. On the other hand, by exposing DAMPs, dying cancer cells change their surface composition, recently indicated as vital for the stimulation of the host immune system and the control of residual ill cells. It is well established that PhotoDynamic Therapy (PDT) for cancer treatment ignites the immune system to elicit a specific antitumor immunity, probably linked to its ability in inducing exposure/release of certain DAMPs, as recently suggested. In the present paper, we discuss the DAMPs associated with PDT and their role in the crossroad between cancer cell death and immunogenicity in PDT.

CD91-Dependent Modulation of Immune Responses by Heat Shock Proteins: A Role in Autoimmunity

Heat shock proteins (HSPs) have been known for decades for their ability to protect cells under stressful conditions. In the 1980s a new role was ascribed for several HSPs given their ability to elicit specific immune responses in the setting of cancer and infectious disease. These immune responses have primarily been harnessed for the immunotherapy of cancer in the clinical setting. However, because of the ability of HSPs to prime diverse immune responses, they have also been used for modulation of immune responses during autoimmunity. The apparent dichotomy of immune responses elicited by HSPs is discussed here on a molecular and cellular level. The potential clinical application of HSP-mediated immune responses for therapy of autoimmune diseases is reviewed.

Heat-shock proteins as endogenous ligands building a bridge between innate and adaptive immunity

There has been growing evidence that heat-shock protein (HSP) functions as an endogenous immunomodulator for innate and adaptive immune responses. Since HSPs inherently act as chaperones within cells, passive release (e.g., by cell necrosis) and active release (including release by secretion in the form of an exosome) have been suggested as mechanisms of HSP release into the extracellular milieu. Such extracellular HSPs have been shown to be activators of innate immune responses through Toll-like receptors. However, it has also been suggested that HSPs augment the ability of associated innate ligands such as lipopolysaccharides to stimulate cytokine production and dendritic cell maturation. More interestingly, a recent study has demonstrated that innate immune responses elicited by danger signals were regulated spatiotemporally and that can be manipulated by HSPs, thereby controlling immune responses. We will discuss how spatiotemporal regulation of HSP-chaperoned molecules within antigen-presenting cells affects adaptive immunity via antigen cross-presentation and innate immune responses. Precise analysis of HSP biology should lead to the establishment of effective HSP-based immunotherapy.

Assessment of roles for calreticulin in the cross-presentation of soluble and bead-associated antigens

Antigen cross-presentation involves the uptake and processing of exogenously derived antigens and their assembly with major histocompatibility complex (MHC) class I molecules. Antigen presenting cells (APC) load peptides derived from the exogenous antigens onto MHC class I molecules for presentation to CD8 T cells. Calreticulin has been suggested to mediate and enhance antigen cross-presentation of soluble and cell-derived antigens. In this study, we examined roles for calreticulin in cross-presentation of ovalbumin using a number of models. Our findings indicate that calreticulin does not enhance in vitro cross-presentation of an ovalbumin-derived peptide, or of fused or bead-associated ovalbumin. Additionally, in vivo, calreticulin fusion or co-conjugation does not enhance the efficiency of CD8 T cell activation by soluble or bead-associated ovalbumin either in wild type mice or in mice lacking Toll-like receptor 4 (TLR4). Furthermore, we detect no significant differences in cross-presentation efficiencies of glycosylated vs. non-glycosylated forms of ovalbumin. Together, these results point to the redundancies in pathways for uptake of soluble and bead-associated antigens.

The most negatively charged low-density lipoprotein L5 induces stress pathways in vascular endothelial cells

BACKGROUND/AIMS

L5, the most negatively charged species of low-density lipoprotein (LDL), has been implicated in atherogenesis by inducing apoptosis of endothelial cells (ECs) and inhibiting the differentiation of endothelial progenitor cells. In this study, we compared the effects of LDL charge on cellular stress pathways leading to atherogenesis.

METHODS

We isolated L5 and L1 (the least negatively charged LDL) from the plasma of patients with familial hypercholesterolemia and used JC-1 staining to examine the effects of L5 and L1 on the mitochondrial membrane potential (DCm) in human umbilical vein ECs (HUVECs). Additionally, we characterized the gene expression profiles of 7 proteins involved in various types of cellular stress.

RESULTS

The DCm was severely compromised in HUVECs treated with L5. Furthermore, compared with L1, L5 induced a decrease in mRNA and protein expression of the endoplasmic reticulum (ER) chaperone proteins ORP150, Grp94, and Grp58, mitochondrial proteins Prdx3 and ATP synthase, and an increase in the expression of the pro-inflammatory protein hnRNP C1/C2.

CONCLUSIONS

Our work suggests that L5, but not L1, may promote the destruction of ECs that occurs during atherogenesis by causing mitochondrial dysfunction and modulating the expression of key proteins to promote inflammation, ER dysfunction, oxidative stress, and apoptosis.

Microglial scavenger receptors and their roles in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is increasing in prevalence with the aging population. Deposition of amyloid-β (Aβ) in the brain of AD patients is a hallmark of the disease and is associated with increased microglial numbers and activation state. The interaction of microglia with Aβ appears to play a dichotomous role in AD pathogenesis. On one hand, microglia can phagocytose and clear Aβ, but binding of microglia to Aβ also increases their ability to produce inflammatory cytokines, chemokines, and neurotoxic reactive oxygen species (ROS). Scavenger receptors, a group of evolutionally conserved proteins expressed on the surface of microglia act as receptors for Aβ. Of particular interest are SCARA-1 (scavenger receptor A-1), CD36, and RAGE (receptor for advanced glycation end products). SCARA-1 appears to be involved in the clearance of Aβ, while CD36 and RAGE are involved in activation of microglia by Aβ. In this review, we discuss the roles of various scavenger receptors in the interaction of microglia with Aβ and propose that these receptors play complementary, nonredundant functions in the development of AD pathology. We also discuss potential therapeutic applications for these receptors in AD.

The role of heat shock proteins in antigen cross presentation

Heat shock proteins (HSPs) are molecular chaperones that bind tumor antigens and mediate their uptake into antigen presenting cells. HSP–antigen complexes are then directed toward either the MHC class I pathway through antigen cross presentation or the conventional class II pathway, leading to activation of T cell subsets. Uptake of HSP-chaperoned polypeptides can involve both receptor-mediated and receptor-independent routes, and mechanisms of antigen sorting between the Class I and II pathways after uptake are currently under investigation. The processes involved in internalization of HSP–antigen complexes differ somewhat from the mechanisms previously determined for (unchaperoned) particulate and free soluble antigens. A number of studies show that HSP-facilitated antigen cross presentation requires uptake of the complexes by scavenger receptors (SR) followed by processing in the proteasome, and loading onto MHC class I molecules. In this review we have examined the roles of HSPs and SR in antigen uptake, sorting, processing, cell signaling, and activation of innate and adaptive immunity.

Prerequisites for the antitumor vaccine-like effect of chemotherapy and radiotherapy

For a long time, anticancer therapies were believed to work (and hence convey a therapeutic benefit) either by killing cancer cells or by inducing a permanent arrest in their cell cycle (senescence). In both scenarios, the efficacy of anticancer regimens was thought to depend on cancer cell-intrinsic features only. More recently, the importance of the tumor microenvironment (including stromal and immune cells) has been recognized, along with the development of therapies that function by modulating tumor cell-extrinsic pathways. In particular, it has been shown that some chemotherapeutic and radiotherapeutic regimens trigger cancer cell death while stimulating an active immune response against the tumor. Such an immunogenic cell death relies on the coordinated emission of specific signals from dying cancer cells and their perception by the host immune system. The resulting tumor-specific immune response is critical for the eradication of tumor cells that may survive therapy. In this review, we discuss the molecular mechanisms that underlie the vaccine-like effects of some chemotherapeutic and radiotherapeutic regimens, with particular attention to the signaling pathways and genetic elements that constitute the prerequisites for immunogenic anticancer therapy.

Heat shock proteins and cancer vaccines: developments in the past decade and chaperoning in the decade to come

Molecular chaperone-peptide complexes extracted from tumors (heat shock protein [HSP] vaccines) have been intensively studied in the preceding two decades, proving to be safe and effective in treating a number of malignant diseases. They offer personalized therapy and target a cross-section of antigens expressed in patients' tumors. Future advances may rely on understanding the molecular underpinnings of this approach to immunotherapy. One property common to HSP vaccines is the ability to stimulate antigen uptake by scavenger receptors on the antigen-presenting cell surface and trigger T-lymphocyte activation. HSPs can also induce signaling through Toll-Like receptors in a range of immune cells and this may mediate the effectiveness of vaccines.