Z39Ig is expressed on macrophages and may mediate inflammatory reactions in arthritis and atherosclerosis

The Relationship Between Echocardiographic Calcification Score and Grade of Knee Osteoarthritis

Background and objective It has been suggested that knee osteoarthritis (KOA) is associated with the development of calcification and an increased risk of cardiovascular (CV) disease, while the contribution of KOA grade is not clearly known enough. This study aimed to investigate the relationship between the grade of KOA, the echocardiographic calcification score (echo-CCS), and CV risk assessment. Methods This cross-sectional study involved 204 patients diagnosed with KOA and classified according to the Kellgren-Lawrence staging criteria. Echo-CCS was obtained according to the presence of calcification in the aortic valve, aortic root, mitral ring, papillary muscle and ventricular septum. Framingham risk score (FRS) was used for CV risk assessment. Results Calcification was detected in 79.4% of patients. The median FRS, echo-CCS, and high-sensitivity C-reactive protein (hs-CRP) levels increased as the KOA grade increased (p<0.05). A one-grade increase in KOA increased the odds of echo-CCS 1-2 group by 5.15 fold (vs. no calcification group) (OR=5.15, p=0.003), while it increased the odds of echo-CCS ≥3 group by 4.61 fold (vs. echo-CCS 1-2 group) (OR=4.61, p=0.003). Median echo-CSS and hs-CRP were higher in the high CV risk group than in the moderate and low CV risk groups. Conclusion The majority of patients with KOA had intracardiac calcification. An increased KOA grade was associated with higher echo-CSS and FRS. These findings indicate that patients with higher grades of KOA may be predisposed to developing subclinical atherosclerosis.

Distinct longevity mechanisms across and within species and their association with aging

Lifespan varies within and across species, but the general principles of its control remain unclear. Here, we conducted multi-tissue RNA-seq analyses across 41 mammalian species, identifying longevity signatures and examining their relationship with transcriptomic biomarkers of aging and established lifespan-extending interventions. An integrative analysis uncovered shared longevity mechanisms within and across species, including downregulated Igf1 and upregulated mitochondrial translation genes, and unique features, such as distinct regulation of the innate immune response and cellular respiration. Signatures of long-lived species were positively correlated with age-related changes and enriched for evolutionarily ancient essential genes, involved in proteolysis and PI3K-Akt signaling. Conversely, lifespan-extending interventions counteracted aging patterns and affected younger, mutable genes enriched for energy metabolism. The identified biomarkers revealed longevity interventions, including KU0063794, which extended mouse lifespan and healthspan. Overall, this study uncovers universal and distinct strategies of lifespan regulation within and across species and provides tools for discovering longevity interventions.

The biology of VSIG4: Implications for the treatment of immune-mediated inflammatory diseases and cancer

V-set and immunoglobulin domain containing 4 (VSIG4), a type I transmembrane receptor exclusively expressed in a subset of tissue-resident macrophages, plays a pivotal role in clearing C3-opsonized pathogens and their byproducts from the circulation. VSIG4 maintains immune homeostasis by suppressing the activation of complement pathways or T cells and inducing regulatory T-cell differentiation, thereby inhibiting the development of immune-mediated inflammatory diseases but enhancing cancer progression. Consequently, VSIG4 exhibits a potential therapeutic effect for immune-mediated inflammatory diseases, but also is regarded as a novel target of immune checkpoint inhibition in cancer therapy. Recently, soluble VSIG4, the extracellular domain of VSIG4, shed from the surface of macrophages, has been found to be a biomarker to define macrophage activation-related diseases. This review mainly summarizes recent new findings of VSIG4 in macrophage phagocytosis and immune homeostasis, and discusses its potential diagnostic and therapeutic usage in infection, inflammation, and cancer.

Therapeutic modulation of V Set and Ig domain-containing 4 (VSIG4) signaling in immune and inflammatory diseases

Inflammation is the result of acute and chronic stresses, caused by emotional or physical trauma, or nutritional or environmental pollutants, and brings serious harm to human life and health. As an important cellular component of the innate immune barrier, the macrophage plays a key role in maintaining tissue homeostasis and promoting tissue repair by controlling infection and resolving inflammation. Several studies suggest that V Set and Ig domain-containing 4 is specifically expressed in tissue macrophages and is associated with a variety of inflammatory diseases. In this paper, we mainly summarize the recent research on V Set and Ig domain-containing 4 structures, functions, function and roles in acute and chronic inflammatory diseases, and provide a novel therapeutic avenue for the treatment of inflammatory diseases, including nervous system, urinary, respiratory and metabolic diseases.

V-Set and immunoglobulin domain containing (VSIG) proteins as emerging immune checkpoint targets for cancer immunotherapy

The development of immune checkpoint inhibitors is becoming a promising approach to fight cancers. Antibodies targeting immune checkpoint proteins such as CTLA-4 and PD-1 can reinvigorate endogenous antitumor T-cell responses and bring durable advantages to several malignancies. However, only a small subset of patients benefit from these checkpoint inhibitors. Identification of new immune checkpoints with the aim of combination blockade of multiple immune inhibitory pathways is becoming necessary to improve efficiency. Recently, several B7 family-related proteins, TIGIT, VSIG4, and VSIG3, which belong to the VSIG family, have attracted substantial attention as coinhibitory receptors during T-cell activation. By interacting with their corresponding ligands, these VSIG proteins inhibit T-cell responses and maintain an immune suppressive microenvironment in tumors. These results indicated that VSIG family members are becoming putative immune checkpoints in cancer immunotherapy. In this review, we summarized the function of each VSIG protein in regulating immune responses and in tumor progression, thus providing an overview of our current understanding of VSIG family members.

Bioinformatics approach to identify the influences of SARS-COV2 infections on atherosclerosis

Coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been a global pandemic since early 2020. Understanding the relationship between various systemic disease and COVID-19 through disease ontology (DO) analysis, an approach based on disease similarity studies, has found that COVID-19 is most strongly associated with atherosclerosis. The study provides new insights for the common pathogenesis of COVID-19 and atherosclerosis by looking for common transcriptional features. Two datasets (GSE152418 and GSE100927) were downloaded from GEO database to search for common differentially expressed genes (DEGs) and shared pathways. A total of 34 DEGs were identified. Among them, ten hub genes with high degrees of connectivity were picked out, namely C1QA, C1QB, C1QC, CD163, SIGLEC1, APOE, MS4A4A, VSIG4, CCR1 and STAB1. This study suggests the critical role played by Complement and coagulation cascades in COVID-19 and atherosclerosis. Our findings underscore the importance of C1q in the pathogenesis of COVID-19 and atherosclerosis. Activation of the complement system can lead to endothelial dysfunction. The DEGs identified in this study provide new biomarkers and potential therapeutic targets for the prevention of atherosclerosis.

Impact of VSIG4 gene polymorphisms on susceptibility and functional status of rheumatoid arthritis

The complement receptor of the immunoglobulin superfamily (CRIg, encoded by the VSIG4 gene) is a macrophage receptor involved in the clearance of immune complexes and autologous cells. Our results suggest that the VSIG4 rs1044165T allele is a risk factor for severe functional status of rheumatoid arthritis in women, possibly by affecting VSIG4 gene expression.

Immune checkpoint protein VSIG4 as a biomarker of aging in murine adipose tissue

Adipose tissue is recognized as a major source of systemic inflammation with age, driving age-related tissue dysfunction and pathogenesis. Macrophages (Mφ) are central to these changes yet adipose tissue Mφ (ATMs) from aged mice remain poorly characterized. To identify biomarkers underlying changes in aged adipose tissue, we performed an unbiased RNA-seq analysis of ATMs from young (8-week-old) and healthy aged (80-week-old) mice. One of the genes identified, V-set immunoglobulin-domain-containing 4 (VSIG4/CRIg), encodes a Mφ-associated complement receptor and B7 family-related immune checkpoint protein. Here, we demonstrate that Vsig4 expression is highly upregulated with age in perigonadal white adipose tissue (gWAT) in two mouse strains (inbred C57BL/6J and outbred NIH Swiss) independent of gender. The accumulation of VSIG4 was mainly attributed to a fourfold increase in the proportion of VSIG4+ ATMs (13%-52%). In a longitudinal study, VSIG4 expression in gWAT showed a strong correlation with age within a cohort of male and female mice and correlated strongly with physiological frailty index (PFI, a multi-parameter assessment of health) in male mice. Our results indicate that VSIG4 is a novel biomarker of aged murine ATMs. VSIG4 expression was also found to be elevated in other aging tissues (e.g., thymus) and was strongly induced in tumor-adjacent stroma in cases of spontaneous and xenograft lung cancer models. VSIG4 expression was recently associated with cancer and several inflammatory diseases with diagnostic and prognostic potential in both mice and humans. Further investigation is required to determine whether VSIG4-positive Mφ contribute to immunosenescence and/or systemic age-related deficits.

Human Dendritic Cells Express the Complement Receptor Immunoglobulin Which Regulates T Cell Responses

The B7 family-related protein V-set and Ig containing 4 (VSIG4), also known as Z39Ig and Complement Immunoglobulin Receptor (CRIg), is the most recent of the complement receptors to be identified, with substantially distinct properties from the classical complement receptors. The receptor displays both phagocytosis-promoting and anti-inflammatory properties. The receptor has been reported to be exclusively expressed in macrophages. We now present evidence, that CRIg is also expressed in human monocyte-derived dendritic cells (MDDC), including on the cell surface, implicating its role in adaptive immunity. Three CRIg transcripts were detected and by Western blotting analysis both the known Long (L) and Short (S) forms were prominent but we also identified another form running between these two. Cytokines regulated the expression of CRIg on dendritic cells, leading to its up- or down regulation. Furthermore, the steroid dexamethasone markedly upregulated CRIg expression, and in co-culture experiments, the dexamethasone conditioned dendritic cells caused significant inhibition of the phytohemagglutinin-induced and alloantigen-induced T cell proliferation responses. In the alloantigen-induced response the production of IFNγ, TNF-α, IL-13, IL-4, and TGF-β1, were also significantly reduced in cultures with dexamethasone-treated DCs. Under these conditions dexamethasone conditioned DCs did not increase the percentage of regulatory T cells (Treg). Interestingly, this suppression could be overcome by the addition of an anti-CRIg monoclonal antibody to the cultures. Thus, CRIg expression may be a control point in dendritic cell function through which drugs and inflammatory mediators may exert their tolerogenic- or immunogenic-promoting effects on dendritic cells.

Pathogen clearance and immune adherence "revisited": Immuno-regulatory roles for CRIg

Rapid elimination of microbes from the bloodstream, along with the ability to mount an adaptive immune response, are essential for optimal host-defense. Kupffer cells are strategically positioned in the liver sinusoids and efficiently capture circulating microbes from the hepatic artery and portal vein, thus preventing bacterial dissemination. In vivo and in vitro studies have probed how complement receptor of the immunoglobulin superfamily (CRIg), also referred to as Z39Ig and V-set and Ig domain-containing 4 (VSIG4), acts as a critical player in pathogen recognition and clearance. While recent data suggested that CRIg may bind bacterial cell wall components directly, the single transmembrane receptor is best known for its interaction with complement C3 opsonization products on the microbial surface. On Kupffer cells, CRIg must capture opsonized microbes against the shear forces of the blood flow. In vivo work reveals how immune adherence (IA), a process in which blood platelets or erythrocytes associate with circulating bacteria, plays a critical role in regulating pathogen capture by CRIg under flow conditions. In addition to its typical innate immune functions, CRIg was shown to directly and indirectly influence adaptive immune responses. Here, we review our current understanding of the diverse roles of CRIg in pathogen elimination, anti-microbial immunity and autoimmunity. In particular, we will explore how, through selective capturing by CRIg, an important balance is achieved between the immunological and clearance functions of liver and spleen.

The immune checkpoint molecule V-set Ig domain-containing 4 is an independent prognostic factor for multiple myeloma

Multiple myeloma (MM) remains as an incurable disease, despite recent substantial improvements in treatment. Therefore, development of novel biomarkers for risk stratification and new therapeutic targets are imperative. One of the emerging treatments for MM is the immune checkpoint blockades. V-set Ig domain-containing 4 (VSIG4) is a lately studied B7-related immune checkpoint modulator. We assessed the VSIG4 expression in patients with MM and its prognostic impact. We analyzed 81 bone marrow and 66 extramedullary biopsy samples of MM patients using immunohistochemistry. VSIG4 mRNA expression data from the Multiple Myeloma Genomics Portal (MMGP) were analyzed to validate our results. The overall survival (OS) of the high VSIG4 expression group was significantly poorer than that of the low VSIG4 expression group (p = 0.046). VSIG4 expression was remained statistically significant after adjustment for revised international staging system (rISS) and Mayo stratification algorithm (mSMART) risk classification, respectively (p = 0.019 and 0.017). Corroborating results were also observed on analyses of VSIG4 expression in patients with extramedullary MM and external data from the MMGP. Our results suggest that VSIG4 expression in MM is an independent indicator of poor prognosis, implying a possible therapeutic target for immunotherapy for MM.

Association between Knee Osteoarthritis, Cardiovascular Risk Factors, and the Framingham Risk Score in South Koreans: A Cross-Sectional Study

Background

Osteoarthritis is a significant burden on personal health and for social cost, and its prevalence is rising. Recent research has revealed an association between osteoarthritis and cardiovascular disease, and this study uses the Framingham risk score (FRS), which is widely used as a composite index of cardiovascular risk factors, to investigate the association between osteoarthritis and various cardiovascular risk factors.

Methods

A total 9,514 participants aged 50 years or older who received knee X-ray diagnosis of the 5th Korean National Health and Nutrition Examination Survey (total surveyees = 24,173) released by the Korean Centers for Disease Control and Prevention was included for analysis. Knee osteoarthritis patients were defined as participants with K-L grade ≥2 on knee X-ray regardless of knee pain. The association between major cardiovascular risk factors (blood pressure, diabetes, cholesterol, and smoking habits), FRS, and knee osteoarthritis was analyzed, adjusting for various covariates.

Results

Prevalence of knee osteoarthritis in Koreans aged ≥50 years was 36.6%, and higher in women (men: 24.9%, women: 45.4%). Prevalence of knee osteoarthritis in participants with hypertension was significantly higher than those without hypertension (fully adjusted odds ratio (OR) 1.26; 95% confidence interval (CI) 1.08–1.48). Knee osteoarthritis prevalence was also higher in participants with impaired fasting glucose or diabetes than those without (age, sex adjusted OR 1.19; 95% CI 1.00–1.41). Also, OR values increased statistically significantly with FRS as a continuous variable (fully adjusted OR 1.007; 95% CI 1.00–1.01).

Conclusions

Prevalence of knee osteoarthritis was associated with hypertension and diabetes, which are major cardiovascular risk factors, and the FRS. Further studies on FRS pertaining to its relationship with osteoarthritis are warranted.

Extracellular stimulation of VSIG4/complement receptor Ig suppresses intracellular bacterial infection by inducing autophagy

VSIG4/CRIg (V-set and immunoglobulin domain containing 4) is a transmembrane receptor of the immunoglobulin superfamily that is expressed specifically on macrophages and mature dendritic cells. VSIG4 signaling accelerates phagocytosis of C3-opsonized bacteria, thereby efficiently clearing pathogens within macrophages. We found that VSIG4 signaling triggered by C3-opsonized Listeria (opLM) or by agonistic anti-VSIG4 monoclonal antibody (mAb) induced macrophages to form autophagosomes. VSIG4-induced autophagosomes were selectively colocalized with the intracellular LM while starvation-induced autophagosomes were not. Consistent with these results, the frequency of autophagosomes induced by infection with opLM was lower in VSIG4-deficient bone marrow-derived macrophages (BMDMs) than in WT BMDMs. Furthermore, when VSIG4 molecules were overexpressed in HeLa cells, which are non-macrophage cells, VSIG4 triggering led to efficient uptake of LM, autophagosome formation, and killing of the infected LM. These findings suggest that VSIG4 signaling not only promotes rapid phagocytosis and killing of C3-opsonized intracellular bacteria, as previously reported, but also induces autophagosome formation, eliminating the LM that have escaped from phagosomes. We conclude that VSIG4 signaling provides an anti-immune evasion mechanism that prevents the outgrowth of intracellular bacteria in macrophages.

VSIG4 expression on macrophages facilitates lung cancer development

Tumor-associated macrophages are a prominent component of lung cancer stroma and contribute to tumor progression. The protein V-set and Ig domain-containing 4 (VSIG4), a novel B7 family-related macrophage protein that has the capacity to inhibit T-cell activation, has a potential role in the development of lung cancer. In this study, 10 human non-small-cell lung cancer specimens were collected and immunohistochemically analyzed for VSIG4 expression. Results showed massive VSIG4(+) cell infiltration throughout the samples. Immunofluorescent double staining showed that VSIG4 was present on CD68(+) macrophages, but absent from CD3(+) T cells, CD31(+) endothelial cells, and CK-18(+) epithelial cells. Moreover, VSIG4 was coexpressed on B7-H1(+) and B7-H3(+) cells in these tumor specimens. Transfection of the VSIG4 gene into 293FT cells demonstrated that the VSIG4 signal could inhibit cocultured CD4(+) and CD8(+) T-cell proliferation and cytokine (IL-2 and IFN-γ) production in vitro. Interestingly, in a murine tumor model induced by Lewis lung carcinoma cell line, we found that tumors grown in VSIG4-deficient (VSIG4(-/-)) mice were significantly smaller than those found in wild-type littermates. All of these results demonstrate that macrophage-associated VSIG4 is an activator that facilitates lung carcinoma development. Specific targeting of VSIG4 may prove to be a novel, efficacious strategy for the treatment of this carcinoma.

Molecular imaging with macrophage CRIg-targeting nanobodies for early and preclinical diagnosis in a mouse model of rheumatoid arthritis

An accurate and noninvasive tracer able to detect molecular events underlying the development of rheumatoid arthritis (RA) would be useful for RA diagnosis and drug efficacy assessment. A complement receptor of the Ig superfamily (CRIg) is expressed on synovial macrophages of RA patients, making it an interesting target for molecular imaging of RA. We aim to develop a radiotracer for the visualization of CRIg in a mouse model for RA using radiolabeled single-domain variable antibody VHH fragments (Nanobodies).

METHODS

Quantitative polymerase chain reaction was used to locate CRIg expression in mice with collagen-induced arthritis (CIA). A Nanobody, NbV4m119, was generated to specifically target CRIg. Flow cytometry, phosphorimaging, and confocal microscopy were used to confirm NbVm119 binding to CRIg-positive cells. SPECT (SPECT/CT) was used to image arthritic lesions in the inflamed paws of 29 mice using (99m)Tc-NbV4m119 Nanobody.

RESULTS

CRIg is constitutively expressed in the liver and was found to be upregulated in synovial tissues of CIA mice. SPECT/CT imaging revealed that (99m)Tc-NbV4m119 specifically targeted CRIg-positive liver macrophages in naïve wild-type but not in CRIg(-/-) (CRIg knockout) mice. In CIA mice, (99m)Tc-NbV4m119 accumulation in arthritic lesions increased according to the severity of the inflammation. In the knees of mice with CIA, (99m)Tc-NbV4m119 was found to accumulate even before the onset of macroscopic clinical symptoms.

CONCLUSION

SPECT/CT imaging with (99m)Tc-NbV4m119 visualizes joint inflammation in CIA. Furthermore, imaging could predict which mice will develop clinical symptoms during CIA. Consequently, imaging of joint inflammation with CRIg-specific Nanobodies offers perspectives for clinical applications in RA patients.

Costimulatory molecule VSIG4 exclusively expressed on macrophages alleviates renal tubulointerstitial injury in VSIG4 KO mice

BACKGROUND

Activation and infiltration of T cells and macrophages are key features of renal tubulointerstitial injury. The costimulatory molecule V-set and immunoglobulin domain-containing protein-4 (VSIG4), which is exclusively expressed on macrophages, is capable of inhibiting the T cell response. However, it is unclear whether VSIG4 is involved in renal tubulointerstitial injury. This study was designed to investigate the role of VSIG4 in renal tubulointerstitial injury and the related T cell infiltration.

METHODS

The unilateral ureteric obstruction (UUO) model of renal inflammation and tubulointerstitial fibrosis was established in VSIG4 transgenic knock-out C57BL/6 mice (VSIG4(-/-)) and wild-type C57BL/6 mice (VSIG4(+/+)). Comparative analysis of renal biological indices were assessed by quantitative real-time PCR and immunofluorescence staining.

RESULTS

Both the VSIG4(-/-) and VSIG4(+/+) mice showed UUO-related temporal changes in renal expression of CD3, CD4 and CD8 T cell markers, with the protein levels being significantly lower in the VSIG4(+/+) UUO mice. Moreover, at each time point examined the UUO VSIG4(+/+) mice showed significantly lower renal mRNA levels of the cytokines interleukin (IL)-2, interferon- and tumor necrosis factor-, but significantly higher IL-10, than the UUO VSIG4(-/-) mice.

CONCLUSIONS

The macrophage-expressed VSIG4 may act to alleviate renal tubulointerstitial injury via inhibition of T cell infiltration and secretion of inflammation related factors.

Long and short non-coding RNAs as regulators of hematopoietic differentiation

Genomic analyses estimated that the proportion of the genome encoding proteins corresponds to approximately 1.5%, while at least 66% are transcribed, suggesting that many non-coding DNA-regions generate non-coding RNAs (ncRNAs). The relevance of these ncRNAs in biological, physiological as well as in pathological processes increased over the last two decades with the understanding of their implication in complex regulatory networks. This review particularly focuses on the involvement of two large families of ncRNAs, namely microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) in the regulation of hematopoiesis. To date, miRNAs have been widely studied, leading to a wealth of data about processing, regulation and mechanisms of action and more specifically, their involvement in hematopoietic differentiation. Notably, the interaction of miRNAs with the regulatory network of transcription factors is well documented whereas roles, regulation and mechanisms of lncRNAs remain largely unexplored in hematopoiesis; this review gathers current data about lncRNAs as well as both potential and confirmed roles in normal and pathological hematopoiesis.

Nuclear factor (NF)-κB and its associated pathways are major molecular regulators of blood-induced joint damage in a murine model of hemophilia

BACKGROUND

The present study was designed to investigate the molecular signaling events from onset of bleeding through the development of arthropathy in a murine model of hemophilia A.

METHODS AND RESULTS

A sharp-injury model of hemarthrosis was used. A global gene expression array on joint-specific RNA isolated 3 h post-injury revealed nuclear factor-kappa B (NF-κB) as the major transcription factor triggering inflammation. As a number of genes encoding the cytokines, growth factors and hypoxia regulating factors are known to be activated by NF-κB and many of these are part of the pathogenesis of various joint diseases, we reasoned that NF-κB-associated pathways may play a crucial role in blood-induced joint damage. To further understand its role, we screened NF-κB-associated pathways between 1 h to 90 days after injury. After a single articular bleed, distinct members of the NF-κB family (NF-κB1/NF-κB2/RelA/RelB) and their responsive pro-inflammatory cytokines (IL-1β/IL-6/IFNγ/TNFα) were significantly up-regulated (> 2 fold, P < 0.05) in injured vs. control joints at the various time-points analyzed (1 h/3 h/7 h/24 h). After multiple bleeds (days 30/60/75/90), there was increased expression of NF-κB-associated factors that contribute to hypoxia (HIF-1α, 3.3-6.5 fold), angiogenesis (VEGF-α, 2.5-4.4 fold) and chondrocyte damage (matrix metalloproteinase-13, 2.8-3.8 fold) in the injured joints. Micro RNAs (miR) that are known to regulate NF-κB activation (miRs-9 and 155), inflammation (miRs-16, 155 and 182) and apoptosis (miRs-19a, 155 and 186) were also differentially expressed (-4 to +13-fold) after joint bleeding, indicating that the small RNAs could modulate the arthropathy phenotype.

CONCLUSIONS

These data suggest that NF-κB-associated signaling pathways are involved in the development of hemophilic arthropathy.

The characteristic expression of B7-associated proteins in Langerhans cell sarcoma

Langerhans cell sarcoma (LCS) is a rare malignancy derived from dendritic cells of the epidermis that is characterized by cytological atypia, frequent mitoses, and aggressive clinical behavior. Cancer-associated B7 molecules including B7-H1, B7-DC, B7-H3 and B7-H4 are thought to be involved in the immunoescape of cancer cells and to function as prognostic markers. However, the expression and distribution of these molecules in LCS have not been described. Here we report that all of these molecules were observed in LCS sample sections by immunohistochemistry analysis. At the cellular level, they were found on the cell membrane and in the cytoplasm. Fluorescence dual staining indicated that B7-H1, B7-H3 and B7-H4 were principally associated with Langerin(+) tumor cells. More interestingly, B7-H1, B7-H3 and B7-H4 were co-expressed on the same tumor cells. Z39Ig, the novel B7-related protein, was also found in the LCS sample sections. Fluorescence dual staining showed that Z39Ig was restricted on CD68(+) macrophages. Our results suggest that B7-H1, B7-H3 and B7-H4 may be potential biomarkers to identify LCS, and a clear understanding of their functional roles may further elucidate the pathogenesis of this carcinoma and potentially contribute to the development of novel immunotherapeutic strategies.

The expression and anatomical distribution of BTLA and its ligand HVEM in rheumatoid synovium

Co-inhibitory signaling from B and T lymphocyte attenuator (BTLA) can suppress lymphocyte activation and maintain peripheral tolerance. However, the expression and anatomical distribution of BTLA and its ligand, herpesvirus entry mediator (HVEM), in rheumatoid arthritis (RA) synovium have not been reported. In this study, we analyzed the expression of HVEM and BTLA in RA synovium by immunohistochemistry, and our results showed that both factors were observed in all four cases of RA samples. At the cellular level, both HVEM and BTLA were found on the cell membrane and in the cytoplasm. Fluorescence dual staining demonstrated that HVEM was chiefly on CD3(+) T cells, CD68(+) macrophages, and to a lesser extent was found on CD31(+) endothelial cells. Similarly, the expression of BTLA was observed on infiltrated CD3(+) T cells and CD68(+) macrophages. The co-expression of HVEM and BTLA with some members of the B7 family in these sections was also analyzed, and the results showed that HVEM antigen was also found on B7-H3(+) capillaries, while it was absent on B7-H1(+), B7-DC(+), B7-H4(+), and Z39Ig(+) cells. Interestingly, BTLA was observed on B7-H1(+), B7-H4(+), and HVEM(+) cells in the synovium. The characteristic expression and distribution of BTLA/HVEM in the synovium indicated that their signaling probably affects the pathogenesis of RA, and a clear understanding of their functional roles may further elucidate the pathogenesis of this disease.

Phenotypic and functional profiles of CRIg (Z39Ig)-expressing macrophages in the large intestine

Intestinal macrophages (Mϕ) play significant roles in maintaining homeostasis by the efficient elimination of foreign particles in the large intestine. However, functional complement receptors have not been fully identified. In this study, we showed that a complement receptor of the Ig superfamily (CRIg, also known as Z39Ig), a receptor for complement fragments (C3b and iC3b), was expressed on a subset of intestinal Mϕ in murine and human large intestine. When abilities of uptake of antigens of murine CRIg+ Mϕ were examined, intestinal CRIg+ Mϕ displayed less endocytic and similar phagocytic abilities compared to resident peritoneal F4/80+CRIg− Mϕ and F4/80+CRIg+ Mϕ. Additionally, we found that a significant portion of C3b-dependent phagocytosis by large intestinal Mϕ involves CRIg, emphasizing the importance of efficient mechanisms to eliminate foreign particles in the large intestine. On the other hand, intestinal Mϕ from 2,4,6-trinitrobenzene sulfonic acid-treated mice had decreased CRIg expression but increased CD11b expression, implying some contribution to the removal of immune complexes. This study will shed new light on opsonization and phagocytosis by large intestinal Mϕ.

Regulation of CRIg expression and phagocytosis in human macrophages by arachidonate, dexamethasone, and cytokines

Although the importance of the macrophage complement receptor immunoglobulin (CRIg) in the phagocytosis of complement opsonized bacteria and in inflammation has been established, the regulation of CRIg expression remains undefined. Because cellular activation during inflammation leads to the release of arachidonate, a stimulator of leukocyte function, we sought to determine whether arachidonate regulates CRIg expression. Adding arachidonate to maturing human macrophages and to prematured CRIg(+) macrophages caused a significant decrease in the expression of cell-surface CRIg and CRIg mRNA. This effect was independent of the metabolism of arachidonate via the cyclooxygenase and lipoxygenase pathways, because it was not inhibited by the nonsteroidal anti-inflammatory drugs indomethacin and nordihydroguaiaretic acid. Studies with specific pharmacological inhibitors of arachidonate-mediated signaling pathways showed that protein kinase C was involved. Administration of dexamethasone to macrophages caused an increase in CRIg expression. Studies with proinflammatory and immunosuppressive cytokines showed that IL-10 increased, but interferon-γ, IL-4, and transforming growth factor-β1 decreased CRIg expression on macrophages. This down- and up-regulation of CRIg expression was reflected in a decrease and increase, respectively, in the phagocytosis of complement opsonized Candida albicans. These data suggest that a unique inflammatory mediator network regulates CRIg expression and point to a mechanism by which arachidonate and dexamethasone have reciprocal effects on inflammation.

Down-regulation of Z39Ig on macrophages by IFN-gamma in patients with chronic HBV infection

Co-inhibitory signals from the B7 superfamily have been demonstrated to induce T cell dysfunction in chronic HBV infection (CHB). However, the expression and function of Z39Ig, a new inhibitor of the B7 superfamily, is still unclear in CHB. Here immunohistochemical staining showed that Z39Ig was restricted to macrophages and that its level was decreased significantly in CHB patients compared to healthy controls. Moreover, reduced Z39Ig expression was positively correlated with plasma HBV load but was inversely related to serum alanine aminotransaminase levels. Further, Z39Ig mRNA had a negative relation to IFN-gamma in vivo, and IFN-gamma also down-regulated Z39Ig expression on monocyte-derived macrophages (MDMs) in a time- and dose-dependent manner in vitro. Interestingly, Z39Ig expression on MDMs was restored when IFN-gamma neutralizing antibodies were added to the T cell/MDM co-culture system, indicating that the IFN-gamma derived from activated-T cells may contribute to the reduction of Z39Ig in the CHB environment. Our results suggest that T cells can opposite T cell hyporesponsiveness through dampening Z39Ig inhibitory signals from macrophages and thus maintain their anti-viral function in CHB. Therefore, decreasing Z39Ig signals from macrophages could contribute to CHB clinical therapy.

Mechanisms of complement activation, C4d deposition, and their contribution to the pathogenesis of antibody-mediated rejection

Complement split products have emerged as useful markers of antibody-mediated rejection in solid organ transplants. One split product, C4d, is now widely accepted as a marker for antibody-mediated rejection in renal and cardiac allografts. This review summarizes the rationale for the use of C4d as a marker of antibody-mediated rejection, along with the clinical evidence supporting its use in the clinical diagnosis of antibody-mediated rejection. Antibody-independent mechanisms by which C4d can be activated by the classical and lectin pathways of complement activation are also identified. Finally, mechanisms by which complement activation stimulates effector cells (neutrophils, monocytes, macrophages, platelets, and B and T lymphocytes) as well as target cells (endothelial cells) are discussed in relation to antibody-mediated allograft rejection.

Complement receptor of the Ig superfamily enhances complement-mediated phagocytosis in a subpopulation of tissue resident macrophages

An important function of the complement cascade is to coat self and foreign particles with C3-proteins that serve as ligands for phagocytic receptors. Although tissue resident macrophages play an important role in complement-mediated clearance, the receptors coordinating this process have not been well characterized. In the present study, we identified a subpopulation of resident peritoneal macrophages characterized by high expression of complement receptor of the Ig superfamily (CRIg), a recently discovered complement C3 receptor. Macrophages expressing CRIg showed significantly increased binding and subsequent internalization of complement-opsonized particles compared with CRIg negative macrophages. CRIg internalized monovalent ligands and was able to bind complement-opsonized targets in the absence of Ca(2+) and Mg(2+), which differs from the beta(2)-integrin CR3 that requires divalent cations and polyvalent ligands for activation of the receptor. Although CRIg dominated in immediate binding of complement-coated particles, CRIg and CR3 contributed independently to subsequent particle phagocytosis. CRIg thus identifies a subset of tissue resident macrophages capable of increased phagocytosis of complement C3-coated particles, a function critical for immune clearance.

Correlation of Peripheral-Blood Gene Expression With the Extent of Coronary Artery Stenosis

Background— The molecular pathophysiology of coronary artery disease (CAD) includes cytokine release and a localized inflammatory response within the vessel wall. The extent to which CAD and its severity is reflected by gene expression in circulating cells is unknown.

Methods and Results— From an initial coronary catheterization cohort we identified 41 patients, comprising 27 cases with angiographically significant CAD and 14 controls without coronary stenosis. Whole-genome microarray analysis performed on peripheral-blood mononuclear cells yielded 526 genes with >1.3-fold differential expression ( P <0.05) between cases and controls. Real-time polymerase chain reaction on 106 genes (the 50 most significant microarray genes and 56 additional literature genes) in an independent subset of 95 patients (63 cases, 32 controls) from the same cohort yielded 14 genes ( P <0.05) that independently discriminated CAD state in a multivariable analysis that included clinical and demographic factors. From an independent second catheterization cohort, 215 patients were selected for real-time polymerase chain reaction–based replication. A case:control subset of 107 patients (86 cases, 21 controls) replicated 11 of the 14 multivariably significant genes from the first cohort. An analysis of the 14 genes in the entire set of 215 patients demonstrated that gene expression was proportional to maximal coronary artery stenosis ( P <0.001 by ANOVA).

Conclusions— Gene expression in peripheral-blood cells reflects the presence and extent of CAD in patients undergoing angiography.

The role of complement in atherosclerosis

PURPOSE OF REVIEW

Although it has long been recognized that atherosclerotic lesions show evidence of complement activation, the functional roles of the complement system in atherogenesis are not yet fully resolved. This article highlights recent publications on the complement system in the atherosclerosis field.

RECENT FINDINGS

There have been a number of recent papers reporting on the association of complement proteins and complement regulators with high density lipoproteins, complement activation by enzymatically-modified LDL, signalling pathways downstream of C3a and C5a receptors and membrane C5b-9 assembly, and the prevention of C5b-9 assembly on endothelial cells via upregulation of CD59 expression in response to arterial laminar flow. C1q has been found to play a protective role in early lesion formation in LDL receptor deficient mice, and Crry-Ig and soluble C1 inhibitor have both been shown to have therapeutic effects in models of vascular injury in ApoE deficient mice. The possibility that the Y402H Factor H polymorphism influences atherosclerosis has been supported in a recent paper showing increased risk in white hypertensive individuals.

SUMMARY

The articles that have emerged over the last year highlight the relevance of the complement system to the atherosclerosis field.

A role of macrophage complement receptor CRIg in immune clearance and inflammation

Complement receptor of the immunoglobulin superfamily (CRIg), also referred to as Z39Ig and V-set and Ig domain-containing 4 (VSIG4), has recently been implicated in the clearance of systemic pathogens and autologous cells. CRIg is exclusively expressed on tissue resident macrophages and binds to multimers of C3b and iC3b that are covalently attached to particle surfaces. Next to functioning as an important clearance receptor, CRIg's extracellular domain inhibits complement activation through the alternative, but not the classical, pathway, providing a novel tool to selectively block this pathway in vivo. Here, we review a role for CRIg in immune clearance, T-cell responses and complement regulation, and discuss the implications for disease manifestation.

Expansion of a unique macrophage subset in rheumatoid arthritis synovial lining layer

The Z39Ig protein (complement receptor for C3b and iC3b) is expressed on resident tissue macrophages in various tissues. This study was undertaken to examine the distribution of Z39Ig+cells and their phenotypic features in rheumatoid arthritis (RA) synovium, in comparison with those of osteoarthritis (OA) and psoriatic arthritis (PsA) synovium. Monoclonal anti-Z39Ig antibody was produced by immunizing Z39Ig transfected murine pre B cells and used for the identification of Z39Ig+cells. Z39Ig+cells were further stained with antibodies to macrophages, fibroblast-like synoviocytes, complement receptors and dendritic cells by using the double immunostaining method in normal, RA, OA and PsA synovium. RA synovial mononuclear cells were double-stained using anti-Z39Ig and anti-CD11c antibodies and sorted into Z39Ig+CD11c+cells and Z39Ig+CD11c-cells. These cell populations were then analysed by electron microscopy. The expression of the Z39Ig protein was limited to intimal macrophages in normal, RA, OA and PsA synovium. The numbers of Z39Ig+CD11c+cells and the ratios of Z39Ig+CD11c+cells to Z39Ig+cells were increased in the synovial lining layer of RA as compared with those of OA and PsA. The ultrastructural analysis of Z39Ig+CD11c+cells showed the character of macrophages with many secondary lysosomes and swelling of mitochondria. Z39Ig+ cells appeared to be useful for identification of resident tissue macrophages in normal synovium and the corresponding macrophages in the synovial lining layer of inflammatory arthritis. Expansion of Z39Ig+CD11c+cells was characteristic of RA synovial lining layer.

Macrophage complement receptors and pathogen clearance

Phagocytosis, an important mechanism of the host-defence system and a primary function of macrophages, is facilitated by opsonization, a process by which serum components tag pathogens for recognition by neutrophils and macrophages. Complement component C3 is central to opsonization. Its first cleavage product, C3b, forms the multisubunit enzyme, C3bBb, which proteolytically cleaves additional C3 molecules on the pathogen surface. C3b is further degraded to iC3b, C3c and C3dg, products that serve as ligands for selective complement receptors on leukocytes. This receptor-ligand interaction subsequently modulates immune responses or directly targets the pathogen for clearance by phagocytosis. Although a central role for C3 in phagocytosis of certain pathogens is well accepted, the receptors orchestrating the phagocytic response have not been well characterized. The recent structures of C3 and its breakdown products have increased our insights into the molecular basis of complement activation and recognition by their receptors. Here we review the biology of macrophage receptors for C3 fragments and discuss their role in the host response to pathogens.

Akt signaling regulates actin organization via modulation of MMP-2 activity during chondrogenesis of chick wing limb bud mesenchymal cells

Endochondral ossification is initiated by the differentiation of mesenchymal precursor cells to chondrocytes. This process is characterized by a strong interdependence of cell shape and cytoskeletal organization accompanying the onset of chondrogenic gene expression, but the molecular mechanisms mediating these interactions are not known. In this study, we hypothesized that the activation of matrix metalloproteinase (MMP)-2 would be involved in the reorganization of the actin cytoskeleton and that this would require an Akt-dependent signaling pathway in chick wing bud mesenchymal cells. The pharmacological inhibition of Akt signaling resulted in decreased glycosaminoglycan synthesis and reduced the level of active MMP-2, leading to suppressed cortical actin organization which is characteristic of differentiated chondrocytes. In addition, the exposure of cells to bafilomycin A1 reversed these chondro-inhibitory effects induced by inhibition of Akt signaling. In conclusion, our data indicate that Akt signaling is involved in the activation of MMP-2 and that this Akt-induced activation of MMP-2 is responsible for reorganization of the actin cytoskeleton into a cortical pattern with parallel rounding of chondrogenic competent cells.