Establishment of an ELISA system for determining soluble LAIR-1 levels in sera of patients with HFRS and kidney transplant

Inhibitory innate receptors and their potential role in transplantation

The regulatory arm of the immune system plays a crucial role in maintaining immune tolerance and preventing excessive immune responses. Immune regulation comprises various regulatory cells and molecules that work together to suppress or regulate immune responses. The programmed cell death protein 1 (PD-1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) are examples of inhibitory receptors that counteract activating signals and fine-tune immune responses. While most of the discoveries of immune regulation have been related to T cells and the adaptive immune system, the innate arm of the immune system also has a range of inhibitory receptors that can counteract activating signals and suppress the effector immune responses. Targeting these innate inhibitory receptors may provide a complementary therapeutic approach in several immune-related conditions, including transplantation. In this review, we will explore the potential role of innate inhibitory receptors in controlling alloimmunity during solid organ transplantation.

LAIR1, an ITIM-Containing Receptor Involved in Immune Disorders and in Hematological Neoplasms

Leukocyte-associated immunoglobulin (Ig)-like receptor 1 (LAIR1, CD305) belongs to the family of immune-inhibitory receptors and is widely expressed on hematopoietic mature cells, particularly on immune cells. Four different types of ligands of LAIR1 have been described, including collagens, suggesting a potential immune-regulatory function on the extracellular matrix. By modulating cytokine secretion and cellular functions, LAIR1 displays distinct patterns of expression among NK cell and T/B lymphocyte subsets during their differentiation and cellular activation and plays a major negative immunoregulatory role. Beyond its implications in physiology, the activity of LAIR1 can be inappropriately involved in various autoimmune or inflammatory disorders and has been implicated in cancer physiopathology, including hematological neoplasms. Its action as an inhibitory receptor can result in the dysregulation of immune cellular responses and in immune escape within the tumor microenvironment. Furthermore, when expressed by tumor cells, LAIR1 can modulate their proliferation or invasion properties, with contradictory pro- or anti-tumoral effects depending on tumor type. In this review, we will focus on its role in normal physiological conditions, as well as during pathological situations, including hematological malignancies. We will also discuss potential therapeutic strategies targeting LAIR1 for the treatment of various autoimmune diseases and cancer settings.

Immunomodulatory Role of the Extracellular Matrix Within the Liver Disease Microenvironment

Chronic liver disease when accompanied by underlying fibrosis, is characterized by an accumulation of extracellular matrix (ECM) proteins and chronic inflammation. Although traditionally considered as a passive and largely architectural structure, the ECM is now being recognized as a source of potent damage-associated molecular pattern (DAMP)s with immune-active peptides and domains. In parallel, the ECM anchors a range of cytokines, chemokines and growth factors, all of which are capable of modulating immune responses. A growing body of evidence shows that ECM proteins themselves are capable of modulating immunity either directly via ligation with immune cell receptors including integrins and TLRs, or indirectly through release of immunoactive molecules such as cytokines which are stored within the ECM structure. Notably, ECM deposition and remodeling during injury and fibrosis can result in release or formation of ECM-DAMPs within the tissue, which can promote local inflammatory immune response and chemotactic immune cell recruitment and inflammation. It is well described that the ECM and immune response are interlinked and mutually participate in driving fibrosis, although their precise interactions in the context of chronic liver disease are poorly understood. This review aims to describe the known pro-/anti-inflammatory and fibrogenic properties of ECM proteins and DAMPs, with particular reference to the immunomodulatory properties of the ECM in the context of chronic liver disease. Finally, we discuss the importance of developing novel biotechnological platforms based on decellularized ECM-scaffolds, which provide opportunities to directly explore liver ECM-immune cell interactions in greater detail.

Inhibitory Receptors and Checkpoints in Human NK Cells, Implications for the Immunotherapy of Cancer

The highly destructive mechanisms by which the immune system faces microbial infections is under the control of a series of inhibitory receptors. While most of these receptors prevent unwanted/excessive responses of individual effector cells, others play a more general role in immunity, acting as true inhibitory checkpoints controlling both innate and adaptive immunity. Regarding human NK cells, their function is finely regulated by HLA-class I-specific inhibitory receptors which allow discrimination between HLA-I⁺, healthy cells and tumor or virus-infected cells displaying loss or substantial alterations of HLA-I molecules, including allelic losses that are sensed by KIRs. A number of non-HLA-specific receptors have been identified which recognize cell surface or extracellular matrix ligands and may contribute to the physiologic control of immune responses and tolerance. Among these receptors, Siglec 7 (p75/AIRM-1), LAIR-1 and IRp60, recognize ligands including sialic acids, extracellular matrix/collagen or aminophospholipids, respectively. These ligands may be expressed at the surface of tumor cells, thus inhibiting NK cell function. Expression of the PD-1 checkpoint by NK cells requires particular cytokines (IL-15, IL-12, IL-18) together with cortisol, a combination that may occur in the microenvironment of different tumors. Blocking of single or combinations of inhibitory receptors unleashes NK cells and restore their anti-tumor activity, with obvious implications for tumor immunotherapy.

Molecular basis of reduced LAIR1 expression in childhood severe malarial anaemia: Implications for leukocyte inhibitory signalling

BACKGROUND

Leukocyte-associated immunoglobulin like receptor-1 (LAIR1) is a transmembrane inhibitory receptor that influences susceptibility to a myriad of inflammatory diseases. Our recent investigations of severe malarial anaemia (SMA) pathogenesis in Kenyan children discovered that novel LAIR1 genetic variants which were associated with decreased LAIR1 transcripts enhanced the longitudinal risk of SMA and all-cause mortality.

METHODS

To characterize the molecular mechanism(s) responsible for altered LAIR1 signalling in severe malaria, we determined LAIR1 transcripts and protein, sLAIR1, sLAIR2, and complement component 1q (C1q) in children with malarial anaemia, followed by a series of in vitro experiments investigating the LAIR1 signalling cascade.

FINDINGS

Kenyan children with SMA had elevated circulating levels of soluble LAIR1 (sLAIR1) relative to non-SMA (1.69-fold P < .0001). The LAIR1 antagonist, sLAIR2, was also elevated in the circulation of children with SMA (1.59 fold-change, P < .0001). There was a positive correlation between sLAIR1 and sLAIR2 (ρ = 0.741, P < .0001). Conversely, circulating levels of complement component 1q (C1q), a LAIR1 natural ligand, were lower in SMA (-1.21-fold P = .048). These in vivo findings suggest that reduced membrane-bound LAIR1 expression in SMA is associated with elevated production of sLAIR1, sLAIR2 (antagonist), and limited C1q (agonist) availability. Since reduced LAIR1 transcripts in SMA were associated with increased acquisition of haemozoin (PfHz) by monocytes (P = .028), we explored the relationship between acquisition of intraleukocytic PfHz, LAIR1 expression, and subsequent impacts on leukocyte signalling in cultured PBMCs from malaria-naïve donors stimulated with physiological concentrations of PfHz (10 μg/mL). Phagocytosis of PfHz reduced LAIR1 transcript and protein expression in a time-dependent manner (P < .050), and inhibited LAIR1 signalling through decreased phosphorylation of LAIR1 (P < .0001) and SH2-domain containing phosphatase-1 (SHP-1) (P < .001). This process was associated with NF-κB activation (P < .0001) and enhanced production of IL-6, IL-1β, and TNF-α (all P < .0001).

INTERPRETATION

Collectively, these findings demonstrate that SMA is characterized by reduced LAIR1 transmembrane expression, reduced C1q, and enhanced production of sLAIR1 and sLAIR2, molecular events which can promote enhanced production of cytokines that contribute to the pathogenesis of SMA. These investigations are important for discovering immune checkpoints that could be future targets of immunotherapy to improve disease outcomes.

Expression of LAIR-1 (CD305) on Human Blood Monocytes as a Marker of Hepatic Cirrhosis Progression

Background and Aim

The presumed role of the inhibitory receptor LAIR-1 (CD305) in the inflammatory response suggests that it might contribute to the pathophysiology of chronic inflammatory diseases such as liver cirrhosis. We studied the LAIR-1 expression on liver macrophages and blood monocytes related to the progression of liver cirrhosis.

Methods

The expression of LAIR-1 was analyzed by immunohistochemistry, flow cytometry, and Western blot.

Results

We found a decreased number of macrophages expressing LAIR-1 in cirrhotic liver that could be due to a high presence of collagen, ligand of LAIR-1, in the fibrotic tissue which could downregulate its expression or interfere with the immunostaining. The expression of LAIR-1 decreased after cell differentiation, and the total content, but not the cell surface expression, increased after activation in the HL-60 human macrophage in vitro model. Blood monocytes exhibited higher LAIR-1 expression levels in cirrhotic patients, which were evident even in early clinical stages in all monocyte subsets, and greater in the "intermediate" inflammatory monocyte subpopulation. The in vitro activation of human blood monocytes did not increase its expression on the cell surface suggesting that the in vivo increase of LAIR-1 must be the result of a specific combination of stimuli present in cirrhotic patients. This represents an exclusive feature of liver cirrhosis, since blood monocytes from other chronic inflammatory pathologies showed similar or lower LAIR-1 levels compared with those of healthy controls.

Conclusions

These results may indicate that monocyte LAIR-1 expression is a new biomarker to early detect liver damage caused by chronic inflammation in liver cirrhosis.

Checkpoint Inhibitors: Applications for Autoimmunity

To limit excessive T cell-mediated inflammatory responses, the immune system has a milieu of inhibitory receptors, called immune checkpoints. Cancer cells have evolved to seize those inhibitory pathways and to prevent T cell-mediated killing of tumor cells. Therefore, immune checkpoint inhibitors (ICI) consisting of blocking antibodies against these receptors present an exciting avenue in the fight against cancer. The last decade has seen the implementation of ICI against a variety of cancer indications that have improved the overall anti-tumor responses and patient survival. However, inflammatory toxicities and autoimmunity are a significant adverse event of ICI therapies. In this review, we will discuss the biology of immune checkpoints, highlight research strategies that may help reduce the incidence of immune-related adverse events associated with ICI therapies, and also suggest investigational approaches to manipulate immune checkpoints to treat primary autoimmune disorders.

SheddomeDB: the ectodomain shedding database for membrane-bound shed markers

BACKGROUND

A number of membrane-anchored proteins are known to be released from cell surface via ectodomain shedding. The cleavage and release of membrane proteins has been shown to modulate various cellular processes and disease pathologies. Numerous studies revealed that cell membrane molecules of diverse functional groups are subjected to proteolytic cleavage, and the released soluble form of proteins may modulate various signaling processes. Therefore, in addition to the secreted protein markers that undergo secretion through the secretory pathway, the shed membrane proteins may comprise an additional resource of noninvasive and accessible biomarkers. In this context, identifying the membrane-bound proteins that will be shed has become important in the discovery of clinically noninvasive biomarkers. Nevertheless, a data repository for biological and clinical researchers to review the shedding information, which is experimentally validated, for membrane-bound protein shed markers is still lacking.

RESULTS

In this study, the database SheddomeDB was developed to integrate publicly available data of the shed membrane proteins. A comprehensive literature survey was performed to collect the membrane proteins that were verified to be cleaved or released in the supernatant by immunological-based validation experiments. From 436 studies on shedding, 401 validated shed membrane proteins were included, among which 199 shed membrane proteins have not been annotated or validated yet by existing cleavage databases. SheddomeDB attempted to provide a comprehensive shedding report, including the regulation of shedding machinery and the related function or diseases involved in the shedding events. In addition, our published tool ShedP was embedded into SheddomeDB to support researchers for predicting the shedding event on unknown or unrecorded membrane proteins.

CONCLUSIONS

To the best of our knowledge, SheddomeDB is the first database for the identification of experimentally validated shed membrane proteins and currently may provide the most number of membrane proteins for reviewing the shedding information. The database included membrane-bound shed markers associated with numerous cellular processes and diseases, and some of these markers are potential novel markers because they are not annotated or validated yet in other databases. SheddomeDB may provide a useful resource for discovering membrane-bound shed markers. The interactive web of SheddomeDB is publicly available at http://bal.ym.edu.tw/SheddomeDB/ .

A non-stimulatory monoclonal antibody against the inhibitory immunoreceptor LAIR-1

The human leukocyte-associated Ig-like receptor (LAIR) family contains two members: LAIR-1 (CD305) and LAIR-2 (CD306). Among them, LAIR-1 is a transmembrane glycoprotein bearing two intracellular immunoreceptor tyrosine-based inhibition motifs (ITIM) and LAIR-2 is soluble. Both molecules bind collagen and LAIR-2 has higher affinity than LAIR-1. LAIR-1 can mediate strong inhibitory signal but the functions of leukocytes expressing LAIR-1 are unclear because of the absence of an effective method to isolate them with resting status. In this study, we generated a monoclonal antibody (MAb) by immunizing BALB/c mice with the recombinant LAIR-2-GST fusion protein, which we termed 3G4. The subclass of 3G4 was identified as IgG1. Specificity analysis by Western blotting demonstrated 3G4 could react with both LAIR-1 and LAIR-2. Unlike another LAIR-1-specific MAb (9.1C3), 3G4 did not inhibit the lysis of target cells P815 by NK cells in a redirected cytotoxicity assay. Preincubation of LAIR-1-transfected K562 cells with 3G4 mildly prevented the binding of LAIR-1 to collagens I and III in a dose-dependent manner. Taken together, the novel MAb 3G4 provides a useful tool to isolate LAIR-1-positive cells without changing their resting state for further application.

Soluble leukocyte-Associated Ig-like Receptor-1 in amniotic fluid is of fetal origin and positively associates with lung compliance

The soluble form of the inhibitory immune receptor leukocyte-Associated Ig-like Receptor-1 (sLAIR-1) is present in plasma, urine and synovial fluid and correlates to inflammation. We and others previously showed inflammatory protein expression in normal amniotic fluid at term. We hypothesized that sLAIR-1 is present in amniotic fluid during term parturition and is related to fetal lung function development. sLAIR-1 was detectable in all amniotic fluid samples (n=355) collected during term spontaneous deliveries. First, potential intra-uterine origins of amniotic fluid sLAIR-1 were explored. Although LAIR-1 was expressed on the surface of amniotic fluid neutrophils, LAIR-1 was not secreted upon ex vivo neutrophil stimulation with LPS, or PMA/ionomycin. Cord blood concentrations of sLAIR-1 were fourfold lower than and not related to amniotic fluid concentrations and placentas showed no or only sporadic LAIR-1 positive cells. Similarly, in post-mortem lung tissue of term neonates that died of non-pulmonary disorders LAIR-1 positive cells were absent or only sporadically present. In fetal urine samples, however, sLAIR-1 levels were even higher than in amniotic fluid and correlated with amniotic fluid sLAIR-1 concentrations. Second, the potential relevance of amniotic fluid sLAIR-1 was studied. sLAIR-1 concentrations had low correlation to amniotic fluid cytokines. We measured neonatal lung function in a convenient subset of 152 infants, using the single occlusion technique, at a median age of 34 days (IQR 30-39). The amniotic fluid concentration of sLAIR-1 was independently correlated to airway compliance (ρ=0.29, P=.001). Taken together, we show the consistent presence of sLAIR-1 in amniotic fluid, which originates from fetal urine. Concentrations of sLAIR-1 in amniotic fluid during term deliveries are independent from levels of other soluble immune mediators. The positive association between concentrations of amniotic fluid sLAIR-1 and neonatal lung compliance suggests that amniotic fluid sLAIR-1 may be useful as a novel independent marker of neonatal lung maturation.

Serum LAIR-2 is increased in autoimmune thyroid diseases

Leukocyte-associated Ig-like receptor (LAIR) is a small family-receptor able to inhibit immune cell function via collagen binding. It exists as both membrane-bound and soluble forms. LAIR-1 functions as an inhibitory receptor on natural killer cells, T lymphocytes and monocytes. In addition to LAIR-1, the human genome encodes LAIR-2, a soluble homolog. Several studies have focused on LAIR-1, whereas few investigations concentrate on the expression and function of LAIR-2. We demonstrate the presence of high LAIR-2 levels in 74/80 sera from patients with autoimmune thyroid diseases (both Graves’ disease and autoimmune thyroiditis). LAIR-2 levels seemed not to be related to specific clinical manifestations, such as thyroid functions (hypo- or hyperthyroidism), or specific clinical features (such as ophtalmopathy). In addition, serum LAIR-2 is able, in vitro, to bind its natural ligand, collagen. Since LAIR-2 has been found to have higher affinity for collagens than LAIR-1 did, we hypothesize a potential regulating capability of serum LAIR-2 in finally regulating the inhibitory capability of LAIR-1.

Expression of leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) on osteoclasts and its potential role in rheumatoid arthritis

OBJECTIVE

Leukocyte-associated immunoglobulin-like receptor-1 is an inhibitory receptor primarily expressed by immune cells. This study was undertaken to define the role of this molecule in osteoclast differentiation and rheumatoid arthritis.

METHODS

In vitro osteoclast assays were performed to characterize the role of Leukocyte-associated immunoglobulin-like receptor-1 in murine and human osteoclastogenesis. Human Leukocyte-associated immunoglobulin-like receptor-1 expression was assessed by immunohistochemistry staining in the synovium of patients with rheumatoid arthritis. The levels of soluble Human Leukocyte-associated immunoglobulin-like receptor-1 were determined by enzyme-linked immunosorbent assay.

RESULTS

We found that multinucleated osteoclast formation from mouse bone marrow cells was inhibited by treatment with a monoclonal antibody against mouse Leukocyte-associated immunoglobulin-like receptor-1 in vitro. By immunohistochemistry, we found that Leukocyte-associated immunoglobulin-like receptor-1 was mainly expressed by macrophages in the inflamed synovial tissue of rheumatoid arthritis patients. In addition, serum and synovial fluid levels of soluble Leukocyte-associated immunoglobulin-like receptor-1 were higher in rheumatoid arthritis patients compared to healthy controls or osteoarthritis patients. Moreover, overexpression of Leukocyte-associated immunoglobulin-like receptor-1 in CD14+ monocytes from healthy volunteers also inhibited human osteoclastogenesis.

CONCLUSION

Collectively, these data demonstrate for the first time that Leukocyte-associated immunoglobulin-like receptor-1 inhibits osteoclastogenesis. Therefore, these results may have therapeutic implications for the treatment of rheumatoid arthritis.

Establishment of reverse direct ELISA and its application in screening high-affinity monoclonal antibodies

Traditionally monoclonal antibody (MAb) titer is determined by indirect enzyme-linked immunosorbent assay (ELISA), which is primarily used to evaluate the quality of MAbs. In this study, the titer and affinity of a group of MAbs against ovalbumin (OVA) were tested by indirect ELISA and the ELISA method reported previously. Data showed that there may be great differences between the indirect ELISA antibody titer and affinity value of MAbs. For the first time, a simple and effective reverse direct ELISA (RD-ELISA) was established for the detection of high-affinity MAbs. Among the group of MAbs to OVA, a certain proportion of antibodies with high affinity but low indirect ELISA titer do exist and can be clearly and efficiently detected by RD-ELISA. This study demonstrates that RD-ELISA is an effective method for high-affinity MAb screening.

Enhanced secretion of leukocyte-associated immunoglobulin-like receptor 2 (LAIR-2) and soluble LAIR-1 in rheumatoid arthritis: LAIR-2 is a more efficient antagonist of the LAIR-1-collagen inhibitory interaction than is soluble LAIR-1

OBJECTIVE

Human leukocyte-associated immunoglobulin-like receptor 1 (hLAIR-1) is an immune inhibitory receptor for collagen that is expressed on most immune cells. We previously showed that the LAIR-1-collagen interaction could be antagonized by the secreted homolog hLAIR-2, which can be detected in the synovial fluid of rheumatoid arthritis (RA) patients. In addition, the extracellular part of hLAIR-1 is a putative antagonist upon shedding from the cell membrane. The purpose of this study was to determine the relative roles of hLAIR-2 and soluble hLAIR-1 (shLAIR-1) in the regulation of the LAIR-1-collagen interaction.

METHODS

The ability of recombinant LAIR proteins to abrogate LAIR-1-collagen binding was tested by flow cytometry and adhesion assays. Collagen binding capacity was analyzed by surface plasmon resonance. Plasma, urine, and synovial fluid were screened for the presence of sLAIR-1 and LAIR-2 by enzyme-linked immunosorbent assay.

RESULTS

Recombinant LAIR-2 proteins abrogated the binding of collagen to LAIR-1 more efficiently than did recombinant sLAIR-1. Consistent with these findings, surface plasmon resonance analysis showed that LAIR-2 had a higher affinity for collagen than did LAIR-1. Activated CD4+ T cells were the main producers of LAIR-2, whereas the source of sLAIR-1 remains elusive. Both soluble LAIR-1 and LAIR-2 could be detected in the plasma and urine of healthy control subjects and patients with RA. Urinary levels of both proteins were significantly increased in RA patients, and LAIR-2 levels in urine were significantly correlated with markers of inflammation.

CONCLUSION

Our data suggest that LAIR-2 is a more potent antagonist of LAIR-1 function in vivo, while both sLAIR-1 and LAIR-2 are potential biomarkers that may be used to monitor urine samples for evidence of systemic inflammation.

Production and Purification of Rabbit's Polyclonal Antibody Against Factor VIII

The attempt is made to produce recombinant factor VIII but the first step in producing such product is production and purification of rabbit's polyclonal antibody against factor VIII. The second and third steps involve monoclonal antibody and recombinant factor VIII production. Factor VIII is one of the most important coagulating factor where its deficiency leads to diseases like hemophilia type A or classic. It is an inherited disease. Previously, it was obtained through fractionation of blood plasma of blood donors. After processing, factor VIII could be used to manage such patients. Due to transfer of viral disease like hepatitis and HIV through factor VIII obtained by fractionation, high cost of production, insufficiency of the donors and the process of virus removal, thus production of factor VIII through recombinant technology can be useful and helpful. The reaction between antibody and antigen is one the most specific reaction; therefore, such reaction can be employed to identify factor VIII. Thereby, rabbits were injected several times with adjuvant-linked antigen to produce antibody. The antibody was separated from the blood sample, purified and used to identify factor VIII in the research.

Leukocyte-associated immunoglobulin-like receptor-1 is expressed on human megakaryocytes and negatively regulates the maturation of primary megakaryocytic progenitors and cell line

Leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) is an inhibitory collagen receptor which belongs to the immunoglobulin (Ig) superfamily. Although the inhibitory function of LAIR-1 has been extensively described in multiple leukocytes, its role in megakaryocyte (MK) has not been explored so far. Here, we show that LAIR-1 is expressed on human bone marrow CD34(+)CD41a(+) and CD41a(+)CD42b(+) cells. LAIR-1 is also detectable in a fraction of human cord blood CD34(+) cell-derived MK that has morphological characteristics of immature MK. In megakaryoblastic cell line Dami, the membrane protein expression of LAIR-1 is up-regulated significantly when cells are treated with phorbol ester phorbol 12-myristate 13-acetate (PMA). Furthermore, cross-linking of LAIR-1 in Dami cells with its natural ligand or anti-LAIR-1 antibody leads to the inhibition of cell proliferation and PMA-promoted differentiation when examined by the MK lineage-specific markers (CD41a and CD42b) and polyploidization. In addition, we also observed that cross-linking of LAIR-1 results in decreased MK generation from primary human CD34(+) cells cultured in a cytokines cocktail that contains TPO. These results suggest that LAIR-1 is a likely candidate for an early marker of MK differentiation, and provide initial evidence indicating that LAIR-1 serves as a negative regulator of megakaryocytopoiesis.

Highly sensitive microplate chemiluminescence enzyme immunoassay for the determination of staphylococcal enterotoxin B based on a pair of specific monoclonal antibodies and its application to various matrices

A highly specific and sensitive microplate chemiluminescent enzyme immunoassay (CLEIA) was established and validated for the detection of staphylococcal enterotoxin B (SEB). A pair of monoclonal antibodies (mAbs) that recognizes different epitopes of SEB was selected from 20 SEB-specific mAbs, and the experimental conditions were examined and optimized for the development of the CLEIA. This method exhibited high performance with a dynamic range of 0.01-5 ng/mL, and the measured limit of detection (LOD) was 0.01 ng/mL. Intra- and interassay coefficient variations were all lower than 13% at three concentrations (0.2, 0.4, and 2 ng/mL). For specificity studies, when this method was applied to test staphylococcal enterotoxins A, C1, and D, no cross-reactivity was observed. It has been successfully applied to the analysis of SEB in a variety of environmental, biological and humoral matrices such as sewage, tap water, river water, roast beef, peanut butter, cured ham, 10% nonfat dry milk, milk, orange juice, and human urine and serum. The aim of this article is to show that the highly sensitive, specific, and simple microplate CLEIA, based on a pair of highly specific monoclonal antibodies, has potential applications for quantifying SEB in public health and military reconnaissance.

Cystatin C, a novel urinary biomarker for sensitive detection of acute kidney injury during haemorrhagic fever with renal syndrome

To explore the value of cystatin C for evaluating acute kidney injury (AKI) in haemorrhagic fever with renal syndrome (HFRS), the concentrations of cystatin C in serum and urine samples from HFRS patients were determined. The serum and urinary cystatin C concentrations significantly increased in HFRS patients compared with normal controls (p < 0.001). In the acute phase of HFRS, urinary cystatin C increased to higher levels than serum creatinine, especially in severe or critical cases in the oliguric stage. Furthermore, higher levels of urinary cystatin C in the acute phase positively correlated with increased severity of the subsequent kidney injury. In conclusion, urinary cystatin C is a more sensitive clinical marker for AKI in HFRS, which may enable us to initiate treatment measures as early as possible.

Leucocyte-associated immunoglobulin-like receptor-1 is an inhibitory regulator of contact hypersensitivity

Leucocyte-associated immunoglobulin-like receptor-1 (LAIR-1) is a membrane receptor of the immunoglobulin (Ig) superfamily that is expressed on most types of haematopoietic cells, and delivers inhibitory signals through interacting with collagens. In order to elucidate the immunological functions of LAIR-1 in vivo, we established transgenic mice expressing a chimeric protein composed of the extracellular domain of LAIR-1 fused with an Ig tag (LAIR-1-Ig), which acts as a decoy by competing with endogenous LAIR-1. The transgenic mice showed an increased susceptibility for development of contact hypersensitivity (CHS), an experimental model of allergic contact dermatitis, in association with enhanced hapten-specific T-cell responses. When T cells from the hapten-sensitized donor mice were transferred into non-sensitized recipients, treatment of either donor mice or recipient mice with LAIR-1-Ig protein accelerated CHS, suggesting a potentially negative role of LAIR-1 in both the sensitization and the elicitation of hapten-reactive T cells. In vitro assays revealed that LAIR-1 decreased the production of interleukin-6 and interleukin-12 in dendritic cells, and inhibited the proliferation and cytokine production of naïve and memory T cells along with G(0)/G(1) cell cycle arrest. Collectively, our findings suggest that LAIR-1 plays a crucial inhibitory role in CHS by regulating antigen-presenting cell and T-cell functions.

The soluble leukocyte-associated Ig-like receptor (LAIR)-2 antagonizes the collagen/LAIR-1 inhibitory immune interaction

Leukocyte-associated Ig-like receptor (LAIR)-1 is a collagen-receptor that inhibits immune cell function upon collagen binding. Next to LAIR-1, the human genome encodes LAIR-2, a putative soluble homolog. In this study we show, for the first time, that the LAIR-2 gene is broadly transcribed in human PBMC, mirroring the expression profile of LAIR-1. LAIR-2 protein is expressed as a soluble receptor exhibiting high affinity for various collagen molecules to which it binds in a hydroxyproline-dependent manner. In vitro stimulation of PBMC induces secretion of LAIR-2. We detect high amounts of LAIR-2 in urine of pregnant women, indicating that the soluble receptor is indeed produced in vivo and can be cleared from the body via urine. Furthermore, LAIR-2 levels are increased in synovial fluid of patients with rheumatoid arthritis as compared with osteoarthritis patients. We hypothesize that soluble LAIR-2 may function as a natural competitor for LAIR-1, thereby regulating its inhibitory potential. Indeed, LAIR-2 prevents binding of human LAIR-1 to collagens and LAIR-1 cross-linking in vitro, suggesting that the protein has an immunoregulatory function in vivo. Hence, we reveal a novel mechanism of immune regulation by a soluble LAIR receptor regulating the inhibitory potential of the membrane-bound LAIR-1 via competition for ligands.

Establishment of a highly sensitive sandwich enzyme-linked immunosorbent assay specific for ovomucoid from hen's egg white

A highly sensitive sandwich enzyme-linked immunosorbent assay (ELISA) kit was established for quantifying ovomucoid from hen's egg white, which has been considered as one of the major allergen in egg white. The detection limit reached 0.041 ng/mL, and linearity ranged from 0.1 to 6.25 ng/mL. Intra- and interassay coefficient variations were all lower than 5% at three concentrations (0.5, 2.5, and 5 ng/mL). No cross-reactivity was observed with bovine serum, horse serum, goat serum, human serum, duck egg white, goose egg white, quail egg white, and pigeon egg white, but a low level of cross-reactivity was found with chicken serum. The ELISA kit was established on the basis of two monoclonal antibodies (mAbs) recognizing different epitopes of ovomucoid. However, these mAbs were generated using commercially purified ovalbumin as immunogen. Studies on the relative allergenicity and antigenicity of egg white protein have been performed by many researchers, but there were controversial opinions reported previously because of the impurity of each egg white protein used in various studies. In the present work we measured the degree of ovomucoid contamination in commercially purified ovalbumin sample, and the value was about 11%. We also determined the ovomucoid residue in influenza vaccine samples for the first time. These data showed that the ELISA kit we established could serve as an effective method for precisely quantifying concentrations of ovomucoid in the egg industry and as a useful tool for the research of allergenicity and antigenicity of hen's egg proteins.

Regulated expression of the inhibitory receptor LAIR-1 on human peripheral T cells during T cell activation and differentiation

The leukocyte-associated Ig-like receptor-1 (LAIR-1) is capable of inhibiting immune cell function through interaction with collagens. LAIR is expressed on the majority of peripheral blood mononuclear cells. The abundant expression of both receptor and ligand calls for regulatory mechanisms to relieve the continuous interaction between collagens and LAIR-1. This regulation may occur at the expression level of the receptor. Here, we report that LAIR-1 is indeed differentially expressed during human T cell differentiation. Naive CD4(+) and CD8(+) T cells as well as CD8(+) T cells of the effector phenotype express higher levels of LAIR-1 compared to memory T cells. In vitro stimulation revealed a decrease in LAIR-1 expression upon activation, and the lower LAIR-1 expression on CD127(-) T cells suggests that activation-induced down-modulation of LAIR-1 may also occur in vivo. Furthermore, crosslinking of LAIR-1 on primary T cells results in an inhibition of T cell function. Our data suggest that regulated expression of LAIR-1 and the subsequent change in the threshold for activation may be a mechanism to modulate inhibition of the immune system.

Non-MHC ligands for inhibitory immune receptors: novel insights and implications for immune regulation

Regulation of cellular responses by inhibitory receptors is crucial for proper function of the immune system. The prototype inhibitory immune receptors are major histocompatibility complex (MHC) class I binding killer-Ig like receptors (KIRs) present on effector cells such as natural killer (NK) cells and effector T cells. However, the recent identification of non-MHC class I ligands for inhibitory immune receptors, such as KLRG1, KLRB1 and LAIR-1, indicates that also MHC class I-independent inhibitory immune receptors play crucial roles in inducing peripheral tolerance. The presence of these receptors on many other immune cell types besides effector cells suggests that tight regulation of cell activation is necessary in all facets of the immune response in both normal and diseased tissue. Here, we review novel insights and implications of non-MHC class I ligand binding to inhibitory immune receptors. We give an overview of the known ligand-receptor pairs by grouping the ligands according to their properties and discuss implications of these interactions for the maintenance of immune balance and for the defense against tumors and pathogens.