Innate Immune Receptors

Neem leaf glycoprotein binding to Dectin-1 receptors on dendritic cell induces type-1 immunity through CARD9 mediated intracellular signal to NFκB

BACKGROUND

A water-soluble ingredient of mature leaves of the tropical mahogany 'Neem' (Azadirachta indica), was identified as glycoprotein, thus being named as 'Neem Leaf Glycoprotein' (NLGP). This non-toxic leaf-component regressed cancerous murine tumors (melanoma, carcinoma, sarcoma) recurrently in different experimental circumstances by boosting prime antitumor immune attributes. Such antitumor immunomodulation, aid cytotoxic T cell (Tc)-based annihilation of tumor cells. This study focused on identifying and characterizing the signaling gateway that initiate this systemic immunomodulation. In search of this gateway, antigen-presenting cells (APCs) were explored, which activate and induce the cytotoxic thrust in Tc cells.

METHODS

Six glycoprotein-binding C-type lectins found on APCs, namely, MBR, Dectin-1, Dectin-2, DC-SIGN, DEC205 and DNGR-1 were screened on bone marrow-derived dendritic cells from C57BL/6 J mice. Fluorescence microscopy, RT-PCR, flow cytometry and ELISA revealed Dectin-1 as the NLGP-binding receptor, followed by verifications through RNAi. Following detection of β-Glucans in NLGP, their interactions with Dectin-1 were explored in silico. Roles of second messengers and transcription factors in the downstream signal were studied by co-immunoprecipitation, western blotting, and chromatin-immunoprecipitation. Intracellularization of FITC-coupled NLGP was observed by processing confocal micrographs of DCs.

RESULTS

Considering extents of hindrance in NLGP-driven transcription rates of the cytokines IL-10 and IL-12p35 by receptor-neutralization, Dectin-1 receptors on dendritic cells were found to bind NLGP through the ligand's peripheral β-Glucan chains. The resulting signal phosphorylates PKCδ, forming a trimolecular complex of CARD9, Bcl10 and MALT1, which in turn activates the canonical NFκB-pathway of transcription-regulation. Consequently, the NFκB-heterodimer p65:p50 enhances Il12a transcription and the p50:p50 homodimer represses Il10 transcription, bringing about a cytokine-based systemic-bias towards type-1 immune environment. Further, NLGP gets engulfed within dendritic cells, possibly through endocytic activities of Dectin-1.

CONCLUSION

NLGP's binding to Dectin-1 receptors on murine dendritic cells, followed by the intracellular signal, lead to NFκB-mediated contrasting regulation of cytokine-transcriptions, initiating a pro-inflammatory immunopolarization, which amplifies further by the responding immune cells including Tc cells, alongside their enhanced cytotoxicity. These insights into the initiation of mammalian systemic immunomodulation by NLGP at cellular and molecular levels, may help uncovering its mode of action as a novel immunomodulator against human cancers, following clinical trials.

The Role of the Microbiome in the Pathogenesis and Treatment of Ulcerative Colitis-A Literature Review

Ulcerative colitis (UC) is a chronic inflammatory bowel disease affecting the colon and rectum. UC's pathogenesis involves colonic epithelial cell abnormalities and mucosal barrier dysfunction, leading to recurrent mucosal inflammation. The purpose of the article is to show the complex interplay between ulcerative colitis and the microbiome. The literature search was conducted using the PubMed database. After a screening process of studies published before October 2023, a total of 136 articles were selected. It has been discovered that there is a fundamental correlation of a robust intestinal microbiota and the preservation of gastrointestinal health. Dysbiosis poses a grave risk to the host organism. It renders the host susceptible to infections and has been linked to the pathogenesis of chronic diseases, with particular relevance to conditions such as ulcerative colitis. Current therapeutic strategies for UC involve medications such as aminosalicylic acids, glucocorticoids, and immunosuppressive agents, although recent breakthroughs in monoclonal antibody therapies have significantly improved UC treatment. Furthermore, modulating the gut microbiome with specific compounds and probiotics holds potential for inflammation reduction, while fecal microbiota transplantation shows promise for alleviating UC symptoms. This review provides an overview of the gut microbiome's role in UC pathogenesis and treatment, emphasizing areas for further research.

Serum Pentraxin 3 as Promising Biomarker for the Long-Lasting Inflammatory Response of COVID-19

Currently, biological markers for COVID-19 disease severity still constitute the main goal of enhancing an efficient treatment to reduce critical consequences such as an abnormal systemic inflammatory response. In this regard, the latest research has shown that Pentraxin 3 (PTX3), a highly conserved innate immunity protein, may serve as a valuable biochemical marker. Based on this evidence, we conducted a case-control study to compare the PTX3 serum levels and several immune-inflammatory mediators of 80 healthcare workers who were subdivided into subjects who were previously infected with SARS-CoV-2 (n = 40) and individuals who were never infected (n = 40). Using a commercially available Enzyme-Linked Immunosorbent Assay (ELISA), PTX3 and various immune-inflammatory protein levels were assessed in serum samples, while also considering possible variables (e.g., gender-related differences). We have shown elevated levels of PTX3 and other inflammatory proteins in previously infected COVID-19-positive subjects (p < 0.001). Moreover, the obtained data also indicate a degree of severity influenced by gender, as shown by the subgroup analysis, in which PTX3 expression was more pronounced in previously COVID-19-positive males (p < 0.001) than in females (p < 0.05) compared to the respective controls. In addition, our data further validate, through a direct comparison of previously COVID-19-positive subjects, greater pro-inflammatory levels in males than in females. Overall, our results may support the validity of PTX3 as a systemic biomarker in prolonged systemic inflammatory responses in the context of COVID-19. Thus, PTX3 modulation could constitute an effective therapeutic strategy for improving the recovery from COVID-19 and its systemic long-term consequences.

The Role of the Microbiome in the Pathogenesis and Treatment of Asthma

The role of the microbiome in the pathogenesis and treatment of asthma is significant. The purpose of this article is to show the interplay between asthma and the microbiome, and main areas that require further research are also highlighted. The literature search was conducted using the PubMed database. After a screening process of studies published before May 2023, a total of 128 articles were selected in our paper. The pre-treatment bronchial microbiome in asthmatic patients plays a role in their responsiveness to treatment. Gut microbiota and its dysbiosis can contribute to immune system modulation and the development of asthma. The association between the microbiome and asthma is complex. Further research is necessary to clarify which factors might moderate that relationship. An appropriate gut microbiome and its intestinal metabolites are a protective factor for asthma development. Prebiotics and certain dietary strategies may have a prophylactic or therapeutic effect, but more research is needed to establish final conclusions. Although the evidence regarding probiotics is ambiguous, and most meta-analyses do not support the use of probiotic intake to reduce asthma, several of the most recent studies have provided promising effects. Further studies should focus on the investigation of specific strains and the examination of their mechanistic and genetic aspects.

The role of NOD-like receptors in innate immunity

The innate immune system in vertebrates and invertebrates relies on conserved receptors and ligands, and pathways that can rapidly initiate the host response against microbial infection and other sources of stress and danger. Research into the family of NOD-like receptors (NLRs) has blossomed over the past two decades, with much being learned about the ligands and conditions that stimulate the NLRs and the outcomes of NLR activation in cells and animals. The NLRs play key roles in diverse functions, ranging from transcription of MHC molecules to initiation of inflammation. Some NLRs are activated directly by their ligands, while other ligands may have indirect effects on the NLRs. New findings in coming years will undoubtedly shed more light on molecular details involved in NLR activation, as well as the physiological and immunological outcomes of NLR ligation.

Therapeutic Targeting of Innate Immune Receptors Against SARS-CoV-2 Infection

The innate immune system is the first line of host's defense against invading pathogens. Multiple cellular sensors that detect viral components can induce innate antiviral immune responses. As a result, interferons and pro-inflammatory cytokines are produced which help in the elimination of invading viruses. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) belongs to Coronaviridae family, and has a single-stranded, positive-sense RNA genome. It can infect multiple hosts; in humans, it is responsible for the novel coronavirus disease 2019 (COVID-19). Successful, timely, and appropriate detection of SARS-CoV-2 can be very important for the early generation of the immune response. Several drugs that target the innate immune receptors as well as other signaling molecules generated during the innate immune response are currently being investigated in clinical trials. In this review, we summarized the current knowledge of the mechanisms underlying host sensing and innate immune responses against SARS-CoV-2 infection, as well as the role of innate immune receptors in terms of their therapeutic potential against SARS-CoV-2. Moreover, we discussed the drugs undergoing clinical trials and the FDA approved drugs against SARS-CoV-2. This review will help in understanding the interactions between SARS-CoV-2 and innate immune receptors and thus will point towards new dimensions for the development of new therapeutics, which can be beneficial in the current pandemic.

HB-EGF Plays a Pivotal Role in Mucosal Hyperplasia During Otitis Media Induced by a Viral Analog

Otitis media (OM), the most common childhood illness, can be caused by bacterial and/or viral infection. Hyperplasia of the middle ear (ME) mucosa is an important component of OM that contributes to its deleterious sequelae. Our previous research revealed that ME mucosal hyperplasia in bacterially induced OM was associated with expression of the heparin-binding epidermal growth factor (HB-EGF) gene, and that HB-EGF induced the proliferation of ME mucosal explants in culture. We used single-cell RNA-Seq to identify ME cells that express Hbegf and related genes involved in mediating responses to this factor. To determine the degree to which a viral infection might induce mucosal hyperplasia, and to assess the role of HB-EGF in hyperplasia in vivo, we used, Poly(I:C) to simulate a ME viral infection, Western blotting to confirm ME protein expression, and a specific inhibitor to block the effects of HB-EGF during OM. Genes for HB-EGF and its receptor were expressed in the ME primarily by epithelial, stromal and endothelial cells. Poly(I:C) induced prominent ME mucosal hyperplasia, peaking two days after ME injection. Immunostaining revealed that cleavage of proHB-EGF into its soluble form (sHB-EGF) was strongly induced in response to Poly(I:C). Inhibition of the sHB-EGF receptor dramatically reduced the hyperplastic response of the mucosa. The results demonstrate that a synthetic analog of viral double-stranded RNA interaction can induce OM including a strong proliferative response of the ME mucosa, independent of bacteria. They also indicate that HB-EGF is the dominant growth factor responsible for ME mucosal hyperplasia in vivo.

Genome-wide CRISPR screens reveal a specific ligand for the glycan-binding immune checkpoint receptor Siglec-7

Glyco-immune checkpoint receptors, molecules that inhibit immune cell activity following binding to glycosylated cell-surface antigens, are emerging as attractive targets for cancer immunotherapy. Defining biologically relevant ligands that bind and activate such receptors, however, has historically been a significant challenge. Here, we present a CRISPRi genomic screening strategy that allowed unbiased identification of the key genes required for cell-surface presentation of glycan ligands on leukemia cells that bind the glyco-immune checkpoint receptors Siglec-7 and Siglec-9. This approach revealed a selective interaction between Siglec-7 and the mucin-type glycoprotein CD43. Further work identified a specific N-terminal glycopeptide region of CD43 containing clusters of disialylated O-glycan tetrasaccharides that form specific Siglec-7 binding motifs. Knockout or blockade of CD43 in leukemia cells relieves Siglec-7-mediated inhibition of immune killing activity. This work identifies a potential target for immune checkpoint blockade therapy and represents a generalizable approach to dissection of glycan-receptor interactions in living cells.

Human umbilical cord mesenchymal stem cells attenuate podocyte injury under high glucose via TLR2 and TLR4 signaling

AIMS

This research aimed to investigate the effects of high glucose (HG) on the innate immunity of podocytes and diabetic nephropathy (DN) mice via Toll like receptor (TLR) signaling, and explore the protective effectsof human umbilical cord mesenchymal stem cells (HUC-MSCs) on this process.

METHODS

HUC-MSCs obtained from human umbilical cord were cocultured with podocytes and transplanted into DN mice. Flow cytometry, CCK-8assay, ELISA, western blot analysis, periodicacid-schiff, masson, immunohistochemistry and immunofluorescence staining was used to detect the inflammation, TLR signaling, physical, biochemical and morphological parameters in podocytes and DN mice.

RESULTS

HG reduced the viability of podocytes, activated TLR2 and TLR4 signaling pathway and increased the expression of inflammatory cytokines such as IL-6, IL-1β, TNF-α, and MCP-1 in podocytes and DN mice. However, HUC-MSCs decreased the inflammation and restrained the TLR signaling pathway caused by HG in vitro and in vivo. Furthermore the rhHGF decreased the expression of TLR2 and TLR4 while the blockade of HGF increased the expression of TLR2 and TLR4 in podocytes.

CONCLUSIONS

HUC-MSCs have benefits to the podocytes under HG and the progression of DN by inhibiting TLR signaling pathway and depressing the inflammation. HUC-MSCs may be a therapeutic strategy for treating patients with DN.

Nuclear Receptors as Multiple Regulators of NLRP3 Inflammasome Function

Nuclear receptors are important bridges between lipid signaling molecules and transcription responses. Beside their role in several developmental and physiological processes, many of these receptors have been shown to regulate and determine the fate of immune cells, and the outcome of immune responses under physiological and pathological conditions. While NLRP3 inflammasome is assumed as key regulator for innate and adaptive immune responses, and has been associated with various pathological events, the precise impact of the nuclear receptors on the function of inflammasome is hardly investigated. A wide variety of factors and conditions have been identified as modulators of NLRP3 inflammasome activation, and at the same time, many of the nuclear receptors are known to regulate, and interact with these factors, including cellular metabolism and various signaling pathways. Nuclear receptors are in the focus of many researches, as these receptors are easy to manipulate by lipid soluble molecules. Importantly, nuclear receptors mediate regulatory mechanisms at multiple levels: not only at transcription level, but also in the cytosol via non-genomic effects. Their importance is also reflected by the numerous approved drugs that have been developed in the past decade to specifically target nuclear receptors subtypes. Researches aiming to delineate mechanisms that regulate NLRP3 inflammasome activation draw a wide range of attention due to their unquestionable importance in infectious and sterile inflammatory conditions. In this review, we provide an overview of current reports and knowledge about NLRP3 inflammasome regulation from the perspective of nuclear receptors, in order to bring new insight to the potentially therapeutic aspect in targeting NLRP3 inflammasome and NLRP3 inflammasome-associated diseases.

ADP-heptose: a bacterial PAMP detected by the host sensor ALPK1

The innate immune response constitutes the first line of defense against pathogens. It involves the recognition of pathogen-associated molecular patterns (PAMPs) by pathogen recognition receptors (PRRs), the production of inflammatory cytokines and the recruitment of immune cells to infection sites. Recently, ADP-heptose, a soluble intermediate of the lipopolysaccharide biosynthetic pathway in Gram-negative bacteria, has been identified by several research groups as a PAMP. Here, we recapitulate the evidence that led to this identification and discuss the controversy over the immunogenic properties of heptose 1,7-bisphosphate (HBP), another bacterial heptose previously defined as an activator of innate immunity. Then, we describe the mechanism of ADP-heptose sensing by alpha-protein kinase 1 (ALPK1) and its downstream signaling pathway that involves the proteins TIFA and TRAF6 and induces the activation of NF-κB and the secretion of inflammatory cytokines. Finally, we discuss possible delivery mechanisms of ADP-heptose in cells during infection, and propose new lines of thinking to further explore the roles of the ADP-heptose/ALPK1/TIFA axis in infections and its potential implication in the control of intestinal homeostasis.

Dynamic Interplay Between Microbiota and Mucosal Immunity in Early Shaping of Asthma and its Implication for the COVID-19 Pandemic

The crosstalk between host immunity and the external environment in the mucous membranes of the gastrointestinal and respiratory tracts in bronchial asthma has recently been scrutinized. There is compelling evidence that the microbiota at these sites may play an important role in the pathogenesis of this chronic airway disease. The appearance of bacteria early in life in the gut before dissemination to the airways plays a pivotal role in shaping mucosal immunity. Loss of microbial diversity or dysbiosis can result in aberrant immune-mediated inflammation and mucosal barrier disruption, which coincides clinically with the successive development of the "allergic march" in asthma. Microbial manipulation may be effective in curbing asthma development by indirectly preserving homeostatic epithelial barrier functions. The protective effects and mechanisms of immunity-microbiome crosstalk at mucosal sites require further investigation to identify therapeutic and preventive measures in asthma. This topical review aims to highlight new evidence that compromised epithelial barrier function, which results in deregulated crosstalk between the microbiome and host mucosal immune system, is an important disease mechanism in asthma. In the light of current COVID-19 pandemic, the collective findings on the impact of mucosal microbiota on the suceptibility to SARS-CoV-2 infection and severity of COVID-19 is explored. The possible therapeutic implications to target these abnormalities are further discussed.

The microbiome and cytosolic innate immune receptors

The discovery of innate immune sensors (pattern recognition receptors, PRRs) has profoundly transformed the notion of innate immunity, in providing a mechanistic basis for host immune interactions with a wealth of environmental signals, leading to a variety of immune-mediated outcomes including instruction and activation of the adaptive immune arm. As part of this growing understanding of host-environmental cross talk, an intimate connection has been unveiled between innate immune sensors and signals perceived from the commensal microbiota, which may be regarded as a hub integrating a variety of environmental cues. Among cytosolic PRRs impacting on host homeostasis by interacting with the commensal microbiota are nucleotide-binding domain, leucine-rich repeat-containing protein receptors (NLRs), together with a number of cytosolic DNA sensors and the family of absent in melanoma (AIM)-like receptors (ALRs). NLR sensors have been a particular focus of research, and some NLRs have emerged as key orchestrators of inflammatory responses and host homeostasis. Some NLRs achieve this through the formation of cytoplasmic multiprotein complexes termed inflammasomes. More recently discovered PRRs include retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), cyclic GMP-AMP synthase (cGAS), and STING. In the present review, they summarize recent advancements in knowledge on structure and function of cytosolic PRRs and their roles in host-microbiota cross talk and immune surveillance. In addition, we discuss their relevance for human health and disease and future therapeutic applications involving modulation of their activation and signaling.

Mass Spectrometry-Based Characterization of the Virion Proteome, Phosphoproteome, and Associated Kinase Activity of Human Cytomegalovirus

The assembly of human cytomegalovirus (HCMV) virions is an orchestrated process that requires, as an essential prerequisite, the complex crosstalk between viral structural proteins. Currently, however, the mechanisms governing the successive steps in the constitution of virion protein complexes remain elusive. Protein phosphorylation is a key regulator determining the sequential changes in the conformation, binding, dynamics, and stability of proteins in the course of multiprotein assembly. In this review, we present a comprehensive map of the HCMV virion proteome, including a refined view on the virion phosphoproteome, based on previous publications supplemented by new results. Thus, a novel dataset of viral and cellular proteins contained in HCMV virions is generated, providing a basis for future analyses of individual phosphorylation steps and sites involved in the orchestrated assembly of HCMV virion-specific multiprotein complexes. Finally, we present the current knowledge on the activity of pUL97, the HCMV-encoded and virion-associated kinase, in phosphorylating viral and host proteins.

The innate immune perspective of autoimmune and autoinflammatory conditions

Innate immunity is one of two immune defence system arms. It is present at birth and does not require ‘learning’ through exposure to foreign organisms. It activates various mechanisms collectively to eliminate pathogens and hold an infection until the adaptive response are mounted. The innate immune system consists of four elements: the epithelial barrier, cells (e.g. macrophages, NK cells), plasma proteins (e.g. complement) and cytokines. These components act in concert to induce complex processes, as well as recruitment, activation and differentiation of adaptive responses. The innate response is more than just the ‘first line of defence’, as it essentially withholds the vast majority of any intruder, has a complex interplay with the adaptive arm and is crucial for survival of the host. Finally, yet importantly, a myriad of diseases has been linked with innate immune dysregulation. In this mini-review we will shed some light on these conditions, particularly regarding autoinflammatory ones.

Plant lectins and their usage in preparing targeted nanovaccines for cancer immunotherapy

Plant lectins, a natural source of glycans with a therapeutic potential may lead to the discovery of new targeted therapies. Glycans extracted from plant lectins are known to act as ligands for C-type lectin receptors (CLRs) that are primarily present on immune cells. Plant-derived glycosylated lectins offer diversity in their N-linked oligosaccharide structures that can serve as a unique source of homogenous and heterogenous glycans. Among the plant lectins-derived glycan motifs, Man₉GlcNAc₂Asn exhibits high-affinity interactions with CLRs that may resemble glycan motifs of pathogens. Thus, such glycan domains when presented along with antigens complexed with a nanocarrier of choice may bewilder the immune cells and direct antigen cross-presentation - a cytotoxic T lymphocyte immune response mediated by CD8⁺ T cells. Glycan structure analysis has attracted considerable interest as glycans are looked upon as better therapeutic alternatives than monoclonal antibodies due to their cost-effectiveness, reduced toxicity and side effects, and high specificity. Furthermore, this approach will be useful to understand whether the multivalent glycan presentation on the surface of nanocarriers can overcome the low-affinity lectin-ligand interaction and thereby modulation of CLR-dependent immune response. Besides this, understanding how the heterogeneity of glycan structure impacts the antigen cross-presentation is pivotal to develop alternative targeted therapies. In the present review, we discuss the findings on structural analysis of glycans from natural lectins performed using GlycanBuilder2 - a software tool based on a thorough literature review of natural lectins. Additionally, we discuss how multiple parameters like the orientation of glycan ligands, ligand density, simultaneous targeting of multiple CLRs and design of antigen delivery nanocarriers may influence the CLR targeting efficacy. Integrating this information will eventually set the ground for new generation immunotherapeutic vaccine design for the treatment of various human malignancies.

Crosstalk between NLRP12 and JNK during Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC), a leading cause of cancer-related death, is initiated and promoted by chronic inflammation. Inflammatory mediators are transcriptionally regulated by several inflammatory signaling pathways, including nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK). cJun N-terminal kinase (JNK), a member of the MAPK family, plays a central role in HCC pathogenesis. Pathogen-associated molecular patterns (PAMPs) activate JNK and other MAPK upon recognition by toll-like receptors (TLRs). Apart from TLRs, PAMPs are sensed by several other pattern recognition receptors, including cytosolic NOD-like receptors (NLRs). In a recent study, we demonstrated that the NLR member NLRP12 plays a critical role in suppressing HCC via negative regulation of the JNK pathway. This article briefly reviews the crosstalk between NLRP12 and JNK that occurs during HCC.

Innate Immune Recognition: An Issue More Complex Than Expected

Primary interaction of an intracellular bacterium with its host cell is initiated by activation of multiple signaling pathways in response to bacterium recognition itself or as cellular responses to stress induced by the bacterium. The leading molecules in these processes are cell surface membrane receptors as well as cytosolic pattern recognition receptors recognizing pathogen-associated molecular patterns or damage-associated molecular patterns induced by the invading bacterium. In this review, we demonstrate possible sequences of events leading to recognition of Francisella tularensis, present findings on known mechanisms for manipulating cell responses to protect Francisella from being killed, and discuss newly published data from the perspective of early stages of host-pathogen interaction.

Inflammation research sails through the sea of immunology to reach immunometabolism

Inflammation occurs as a result of acute trauma, invasion of the host by different pathogens, pathogen-associated molecular patterns (PAMPs) or chronic cellular stress generating damage-associated molecular patterns (DAMPs). Thus inflammation may occur under both sterile inflammatory conditions including certain cancers, autoimmune or autoinflammatory diseases (Rheumatic arthritis (RA)) and infectious diseases including sepsis, pneumonia-associated acute lung inflammation (ALI) or acute respiratory distress syndrome (ARDS). The pathogenesis of inflammation involves dysregulation of an otherwise protective immune response comprising of various innate and adaptive immune cells and humoral (cytokines and chemokines) mediators secreted by these immune cells upon the activation of signaling mechanisms regulated by the activation of different pattern recognition receptors (PRRs). However, the pro-inflammatory and anti-inflammatory action of these immune cells is determined by the metabolic stage of the immune cells. The metabolic process of immune cells is called immunometabolism and its shift determined by inflammatory stimuli is called immunometabolic reprogramming. The article focuses on the involvement of various immune cells generating the inflammation, their interaction, immunometabolic reprogramming, and the therapeutic targeting of the immunometabolism to manage inflammation.

NOD-like receptors: major players (and targets) in the interface between innate immunity and cancer

Innate immunity comprises several inflammation-related modulatory pathways which receive signals from an array of membrane-bound and cytoplasmic pattern recognition receptors (PRRs). The NLRs (NACHT (NAIP (neuronal apoptosis inhibitor protein), C2TA (MHC class 2 transcription activator), HET-E (incompatibility locus protein from Podospora anserina) and TP1 (telomerase-associated protein) and Leucine-Rich Repeat (LRR) domain containing proteins) relate to a large family of cytosolic innate receptors, involved in detection of intracellular pathogens and endogenous byproducts of tissue injury. These receptors may recognize pathogen-associated molecular patterns (PAMPs) and/or danger-associated molecular patterns (DAMPs), activating host responses against pathogen infection and cellular stress. NLR-driven downstream signals trigger a number of signaling circuitries, which may either initiate the formation of inflammasomes and/or activate nuclear factor κB (NF-κB), stress kinases, interferon response factors (IRFs), inflammatory caspases and autophagy. Disruption of those signals may lead to a number of pro-inflammatory conditions, eventually promoting the onset of human malignancies. In this review, we describe the structures and functions of the most well-defined NLR proteins and highlight their association and biological impact on a diverse number of cancers.

The Absent in Melanoma 2-Like Receptor IFN-Inducible Protein 16 as an Inflammasome Regulator in Systemic Lupus Erythematosus: The Dark Side of Sensing Microbes

Absent in melanoma 2 (AIM2)-like receptors (ALRs) are a newly characterized class of pathogen recognition receptors (PRRs) involved in cytosolic and nuclear pathogen DNA recognition. In recent years, two ALR family members, the interferon (IFN)-inducible protein 16 (IFI16) and AIM2, have been linked to the pathogenesis of various autoimmune diseases, among which systemic lupus erythematosus (SLE) has recently gained increasing attention. SLE patients are indeed often characterized by constitutively high serum IFN levels and increased expression of IFN-stimulated genes due to an abnormal response to pathogens and/or incorrect self-DNA recognition process. Consistently, we and others have shown that IFI16 is overexpressed in a wide range of autoimmune diseases where it triggers production of specific autoantibodies. In addition, evidence from mouse models supports a model whereby ALRs are required for IFN-mediated host response to both exogenous and endogenous DNA. Following interaction with cytoplasmic or nuclear nucleic acids, ALRs can form a functional inflammasome through association with the adaptor ASC [apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD)] and with procaspase-1. Importantly, inflammasome-mediated upregulation of IL-1β and IL-18 production positively correlates with SLE disease severity. Therefore, targeting ALR sensors and their downstream pathways represents a promising alternative therapeutic approach for SLE and other systemic autoimmune diseases.

Leucine-rich repeats containing protein functions in the antibacterial immune reaction in stomach of kuruma shrimp Marsupenaeus japonicus

Leucine rich repeat (LRR) motif exists in many immune receptors of animals and plants. Most LRR containing (LRRC) proteins are involved in protein-ligand and protein-protein interaction, but the exact functions of most LRRC proteins were not well-studied. In this study, an LRRC protein was identified from kuruma shrimp Marsupenaeus japonicus, and named as MjLRRC1. MjLRRC1 was consistently expressed in different tissues of normal shrimp with higher expression in gills and stomach. At the transcriptional level, there were no significant changes of MjLRRC1 after injection of Vibrio anguillarum or Staphylococcus aureus in gills and hepatopancreas. While in V. anguillarum oral infection, MjLRRC1 was upregulated in stomach but not in intestine. The recombinant MjLRRC1 protein could bind to Gram-positive and Gram-negative bacteria, bacterial cell wall components including peptidoglycan, lipoteichoic acid, and lipopolysaccharide. MjLRRC1 regulated the expression of some antimicrobial peptide (AMP) genes and participated in bacteria clearance of stomach. All these results suggested that MjLRRC1 might play important roles in antibacterial immune response of kuruma shrimp.