Shedding of large functionally active CD11/CD18 Integrin complexes from leukocyte membranes during synovial inflammation distinguishes three types of arthritis through differential epitope exposure

Association of integrin-β2 polymorphism and expression with the risk of rheumatoid arthritis and osteoarthritis in Egyptian patients

BACKGROUND

The genetic architecture of rheumatoid arthritis (RA) and osteoarthritis (OA) are still unclear. Although RA and OA have quite different causes, they share synovial inflammation, risk factors, and some disease-associated genes, including the integrin subunit β2 (ITGB2)/CD18 gene involved in extracellular matrix interactions and immune cell signaling. However, the functional role of ITGB2 genetic variants, its circulating expression pattern, and their clinical usefulness in RA and OA remain unexplored. Our study appraised the association of ITGB2 rs2070946 single nucleotide polymorphism with the vulnerability to RA and OA and its influence on ITGB2 mRNA expression, along with the potential of serum ITGB2 expression in RA and OA diagnosis.

METHODS

This study included 70 RA patients, 70 primary OA patients, and 60 healthy volunteers. Genotyping and gene expression analysis were performed using qPCR. Bioinformatics analysis was employed to construct the protein-protein interaction (PPI) network of ITGB2.

RESULTS

Serum ITGB2 mRNA expression was upregulated in both RA and OA compared to healthy controls. ITGB2 rs2070946 was associated with escalating risk of both diseases. RA patients harboring the rs2070946 CC or TC + CC genotypes had higher serum ITGB2 expression than the TT genotype carriers. Likewise, OA patients having the minor homozygote CC genotype had higher serum ITGB2 expression than those carrying the TT, TC or TT + TC genotypes. Serum ITGB2 expression showed profound diagnostic potential for RA and OA in receiver-operating characteristic analysis. In RA, serum ITGB2 expression positively correlated with rheumatoid factor and disease activity score 28 (DAS28). The ITGB2-PPI network enriched in cell-cell adhesion, ICAM-3 receptor activity, T-cell activation, leukocyte adhesion, complement binding, and NF-κB, tumor necrosis factor, and interleukin signaling pathways.

CONCLUSION

These findings embrace the impact of ITGB2 rs2070946 as a novel genetic biomarker of both RA and OA, which could alter the ITGB2 expression. Serum ITGB2 expression could aid in timely diagnosis of RA and OA.

Soluble ITGaM and ITGb2 Integrin Subunits Are Involved in Long-Term Pulmonary Complications after COVID-19 Infection

(1) Introduction: The role of soluble integrins in post-COVID-19 complications is unclear, especially in long-term pulmonary lesions. The purpose of this study was to investigate the association between soluble ITGa2, ITGaM and ITGb2 integrin subunits and long COVID-19 pulmonary complications. (2) Methodology: Post-COVID-19 patients were enrolled. According to the evidence of persistent interstitial lung lesions on CT, patients were divided into a long-term pulmonary complications group (P(+)) and a control group without long-term pulmonary complications (P(-)). We randomly selected 80 patients for further investigation (40 subjects for each group). Levels of ITGa2, ITGaM and ITGb2 integrin subunits were determined by ELISA assay. (3) Results: The serum concentration of sITGaM and sITGb2 were significantly higher in the P(+) group (sITGaM 18.63 ng/mL [IQR 14.17-28.83] vs. 14.75 ng/mL [IQR 10.91-20] p = 0.01 and sITGb2 10.55 ng/mL [IQR 6.53-15.83] vs. 6.34 ng/mL [IQR 4.98-9.68] p = 0.002). We observed a statistically significant correlation between sITGaM and sITGb2 elevation in the P(+) group (R = 0.42; p = 0.01). Patients from the P(+) group had a lower (1.82 +/-0.84 G/L) lymphocyte level than the P(-)group (2.28 +/-0.79 G/L), p = 0.03. Furthermore, we observed an inverse correlation in the P(-) group between blood lymphocyte count and sITGb2 integrin subunit levels (R = -0.49 p = 0.01). (4) Conclusions: Elevated concentrations of sITGaM and sITGb2 were associated with long-term pulmonary complications in post-COVID-19 patients. Both sITGaM and sITGb2 may be promising biomarkers for predicting pulmonary complications and could be a potential target for therapeutic intervention in post-COVID-19 patients.

Identification of susceptibility modules and hub genes of osteoarthritis by WGCNA analysis

Osteoarthritis (OA) is a major cause of pain, disability, and social burden in the elderly throughout the world. Although many studies focused on the molecular mechanism of OA, its etiology remains unclear. Therefore, more biomarkers need to be explored to help early diagnosis, clinical outcome measurement, and new therapeutic target development. Our study aimed to retrieve the potential hub genes of osteoarthritis (OA) by weighted gene co-expression network analysis (WGCNA) and assess their clinical utility for predicting OA. Here, we integrated WGCNA to identify novel OA susceptibility modules and hub genes. In this study, we first selected 477 and 834 DEGs in the GSE1919 and the GSE55235 databases, respectively, from the Gene Expression Omnibus (GEO) website. Genes with p-value<0.05 and | log2FC | > 1 were included in our analysis. Then, WGCNA was conducted to build a gene co-expression network, which filtered out the most relevant modules and screened out 23 overlapping WGCNA-derived hub genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses elucidated that these hub genes were associated with cell adhesion molecules pathway, leukocyte activation, and inflammatory response. In addition, we conducted the protein–protein interaction (PPI) network in 23 hub genes, and the top four upregulated hub genes were sorted out (CD4, SELL, ITGB2, and CD52). Moreover, our nomogram model showed good performance in predicting the risk of OA (C-index = 0.76), and this model proved to be efficient in diagnosis by ROC curves (AUC = 0.789). After that, a single-sample gene set enrichment (ssGSEA) analysis was performed to discover immune cell infiltration in OA. Finally, human primary synoviocytes and immunohistochemistry study of synovial tissues confirmed that those candidate genes were significantly upregulated in the OA groups compared with normal groups. We successfully constructed a co-expression network based on WGCNA and found out that OA-associated susceptibility modules and hub genes, which may provide further insight into the development of pre-symptomatic diagnosis, may contribute to understanding the molecular mechanism study of OA risk genes.

Global Proteomic Analyses Reveals Abnormal Immune Regulation in Patients With New Onset Ankylosing Spondylitis

Background

Ankylosing spondylitis (AS) is a chronic inflammatory disease with serious consequences and a high rate of morbidity and mortality, In our previous work, we reveal the key features of proteins in new-onset ankylosing spondylitis patients.

Material and Methods

Ankylosing spondylitis (AS) is a chronic inflammatory condition that affects the spine, and inflammation plays an essential role in AS pathogenesis. The inflammatory process in AS, however, is still poorly understood due to its intricacy. Systematic proteomic and phosphorylation analyses of peripheral blood mononuclear cells (PBMCs) were used to investigate potential pathways involved in AS pathogenesis.

Results

Liquid chromatography-tandem mass spectrometry (LC–MS/MS) analysis was performed and discovered 782 differentially expressed proteins (DEPs) and 122 differentially phosphorylated proteins (DPPs) between 9 new-onset AS patients and 9 healthy controls. The DEPs were further verified using parallel reaction monitoring (PRM) analysis. PRM analysis verified that 3 proteins (HSP90AB1, HSP90AA1 and HSPA8) in the antigen processing and presentation pathway, 6 proteins (including ITPR1, MYLK and STIM1) in the platelet activation pathway and 10 proteins (including MYL12A, MYL9 and ROCK2) in the leukocyte transendothelial migration pathway were highly expressed in the PBMCs of AS patients.

Conclusion

The key proteins involved in antigen processing and presentation, platelet activation and leukocyte transendothelial migration revealed abnormal immune regulation in patients with new-onset AS. These proteins might be used as candidate markers for AS diagnosis and new therapeutic targets, as well as elucidating the pathophysiology of AS.

A possible molecular mechanism for mechanotransduction at cellular focal adhesion complexes

Mechanotransduction at focal adhesion complexes is key for various cellular events. Theoretical analyses were performed to predict a potential role of lipid membranes in modulating mechanotransduction at focal adhesions. Calculations suggested that the size of nanostructural constraints and mechanical pulling applied on lipid membranes affect the generation of cellular traction forces and signaling transduction at focal adhesions. This work provides predictions on how lipid membranes contribute to mechanotransduction at cellular focal adhesions.

A shedding soluble form of interleukin-17 receptor D exacerbates collagen-induced arthritis through facilitating TNF-α-dependent receptor clustering

Rheumatoid arthritis (RA) is exacerbated by TNF-alpha signaling. However, it remains unclear whether TNF-α-activated TNFR1 and TNFR2 are regulated by extracellular factors. Here, we showed that soluble glycosylated interleukin-17 receptor D (sIL-17RD), which was produced by proteolytic cleavage, enhanced TNF-α-induced RA. We revealed that IL-17RD shedding was induced by the proteolytic enzyme TACE and enhanced by TNF-α expression in macrophages. Intriguingly, sIL-17RD was elevated in the sera of arthritic mice and rats. Recombinant sIL-17RD significantly enhanced the TNF-α-induced proinflammatory response by promoting TNF-α-TNFR-sIL-17RD complex formation and receptor clustering, leading to the accelerated development of collagen-induced arthritis. Our observations revealed that ectodomain shedding of IL-17RD occurred in RA to boost the TNF-α-induced inflammatory response. Targeting sIL-17RD may provide a new strategy for the therapy of RA.

Anti-inflammatory effect of sulforaphane on LPS-stimulated RAW 264.7 cells and ob/ob mice

Background

Sulforaphane (SFN) is an isothiocyanate compound present in cruciferous vegetables. Although the anti-inflammatory effects of SFN have been reported, the precise mechanism related to the inflammatory genes is poorly understood.

Objectives

This study examined the relationship between the anti-inflammatory effects of SFN and the differential gene expression pattern in SFN treated ob/ob mice.

Methods

Nitric oxide (NO) level was measured using a Griess assay. The inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression levels were analyzed by Western blot analysis. Pro-inflammatory cytokines (tumor necrosis factor [TNF]-α, interleukin [IL]-1β, and IL-6) were measured by enzyme-linked immunosorbent assay (ELISA). RNA sequencing analysis was performed to evaluate the differential gene expression in the liver of ob/ob mice.

Results

The SFN treatment significantly attenuated the iNOS and COX-2 expression levels and inhibited NO, TNF-α, IL-1β, and IL-6 production in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. RNA sequencing analysis showed that the expression levels of 28 genes related to inflammation were up-regulated (> 2-fold), and six genes were down-regulated (< 0.6-fold) in the control ob/ob mice compared to normal mice. In contrast, the gene expression levels were restored to the normal level by SFN. The protein-protein interaction (PPI) network showed that chemokine ligand (Cxcl14, Ccl1, Ccl3, Ccl4, Ccl17) and chemokine receptor (Ccr3, Cxcr1, Ccr10) were located in close proximity and formed a “functional cluster” in the middle of the network.

Conclusions

The overall results suggest that SFN has a potent anti-inflammatory effect by normalizing the expression levels of the genes related to inflammation that were perturbed in ob/ob mice.

Insights Into Leukocyte Trafficking in Inflammatory Arthritis - Imaging the Joint

The inappropriate accumulation and activation of leukocytes is a shared pathological feature of immune-mediated inflammatory diseases (IMIDs), such as rheumatoid arthritis (RA) and psoriatic arthritis (PsA). Cellular accumulation is therefore an attractive target for therapeutic intervention. However, attempts to modulate leukocyte entry and exit from the joint have proven unsuccessful to date, indicating that gaps in our knowledge remain. Technological advancements are now allowing real-time tracking of leukocyte movement through arthritic joints or in vitro joint constructs. Coupling this technology with improvements in analyzing the cellular composition, location and interactions of leukocytes with neighboring cells has increased our understanding of the temporal dynamics and molecular mechanisms underpinning pathological accumulation of leukocytes in arthritic joints. In this review, we explore our current understanding of the mechanisms leading to inappropriate leukocyte trafficking in inflammatory arthritis, and how these evolve with disease progression. Moreover, we highlight the advances in imaging of human and murine joints, along with multi-cellular ex vivo joint constructs that have led to our current knowledge base.

CD11b Signaling Prevents Chondrocyte Mineralization and Attenuates the Severity of Osteoarthritis

Osteoarthritis (OA) is a progressive joint disease that is strongly associated with calcium-containing crystal formation (mineralization) by chondrocytes leading ultimately to cartilage calcification. However, this calcification process is poorly understood and treatments targeting the underlying disease mechanisms are lacking. The CD11b/CD18 integrin (Mac-1 or αMβ2), a member of the beta 2 integrin family of adhesion receptors, is critically involved in the development of several inflammatory diseases, including rheumatoid arthritis and systemic lupus erythematosus. We found that in a collagen-induced arthritis, CD11b-deficient mice exhibited increased cartilage degradation compared to WT control animals. However, the functional significance of CD11b integrin signaling in the pathophysiology of chondrocytes remains unknown. CD11b expression was found in the extracellular matrix and in chondrocytes in both healthy and damaged human and murine articular cartilage. Primary murine CD11b KO chondrocytes showed increased mineralization when induced in vitro by secondary calciprotein particles (CPP) and quantified by Alizarin Red staining. This increased propensity to mineralize was associated with an increased alkaline phosphatase (Alp) expression (measured by qRT-PCR and activity assay) and an enhanced secretion of the pro-mineralizing IL-6 cytokine compared to control wild-type cells (measured by ELISA). Accordingly, addition of an anti-IL-6 receptor antibody to CD11b KO chondrocytes reduced significantly the calcification and identified IL-6 as a pro-mineralizing factor in these cells. In the same conditions, the ratio of qRT-PCR expression of collagen X over collagen II, and that of Runx2 over Sox9 (both ratio being indexes of chondrocyte hypertrophy) were increased in CD11b-deficient cells. Conversely, the CD11b activator LA1 reduced chondrocyte mineralization, Alp expression, IL-6 production and collagen X expression. In the meniscectomy (MNX) model of murine knee osteoarthritis, deficiency of CD11b led to more severe OA (OARSI scoring of medial cartilage damage in CD11b: 5.6 ± 1.8, in WT: 1.2 ± 0.5, p < 0.05, inflammation in CD11b: 2.8 ± 0.2, in WT: 1.4 ± 0.5). In conclusion, these data demonstrate that CD11b signaling prevents chondrocyte hypertrophy and chondrocyte mineralization in vitro and has a protective role in models of OA in vivo.

Kinin B1 Receptor Is Important in the Pathogenesis of Myeloperoxidase-Specific ANCA GN

BACKGROUND

Myeloperoxidase-specific ANCA (MPO-ANCA) are implicated in the pathogenesis of vasculitis and GN. Kinins play a major role during acute inflammation by regulating vasodilatation and vascular permeability and by modulating adhesion and migration of leukocytes. Kinin system activation occurs in patients with ANCA vasculitis. Previous studies in animal models of GN and sclerosing kidney diseases have demonstrated protective effects of bradykinin receptor 1 (B1R) blockade via interference with myeloid cell trafficking.

METHODS

To investigate the role of B1R in a murine model of MPO-ANCA GN, we evaluated effects of B1R genetic ablation and pharmacologic blockade. We used bone marrow chimeric mice to determine the role of B1R in bone marrow-derived cells (leukocytes) versus nonbone marrow-derived cells. We elucidated mechanisms of B1R effects using in vitro assays for MPO-ANCA-induced neutrophil activation, endothelial adherence, endothelial transmigration, and neutrophil adhesion molecule surface display.

RESULTS

B1R deficiency or blockade prevented or markedly reduced ANCA-induced glomerular crescents, necrosis, and leukocyte influx in mice. B1R was not required for in vitro MPO-ANCA-induced neutrophil activation. Leukocyte B1R deficiency, but not endothelial B1R deficiency, decreased glomerular neutrophil infiltration induced by MPO-ANCA in vivo. B1R enhanced ANCA-induced neutrophil endothelial adhesion and transmigration in vitro. ANCA-activated neutrophils exhibited changes in Mac-1 and LFA-1, important regulators of neutrophil endothelial adhesion and transmigration: ANCA-activated neutrophils increased surface expression of Mac-1 and increased shedding of LFA-1, whereas B1R blockade reduced these effects.

CONCLUSIONS

The leukocyte B1R plays a critical role in the pathogenesis of MPO-ANCA-induced GN in a mouse model by modulating neutrophil-endothelial interaction. B1R blockade may have potential as a therapy for ANCA GN and vasculitis.

Effect of soluble cleavage products of important receptors/ligands on efferocytosis: Their role in inflammatory, autoimmune and cardiovascular disease

Efferocytosis, the clearance of apoptotic cells (ACs), is a physiologic, multifaceted and dynamic process and a fundamental mechanism for the preservation of tissue homeostasis by avoiding unwanted inflammation and autoimmune responses through special phagocytic receptors. Defective efferocytosis is associated with several disease states, including cardiovascular disease and impaired immune surveillance, as occurs in cancer and autoimmune disease. A major cause of defective efferocytosis is non-functionality of surface receptors on either the phagocytic cells or the ACs, such as TAM family tyrosine kinase, which turns to a soluble form by cleavage/shedding or alternative splicing. Recently, soluble forms have featured prominently as potential biomarkers, indicative of prognosis and enabling targeted therapy using several commonly employed drugs and inhibitors, such as bleomycin, dexamethasone, statins and some matrix metalloproteinase inhibitors such as TAPI-1 and BB3103. Importantly, to design drug carriers with enhanced circulatory durability, the adaptation of soluble forms of physiological receptors/ligands has been purported. Research has shown that soluble forms are more effective than antibody forms in enabling targeted treatment of certain conditions, such as autoimmune diseases. In this review, we sought to summarize the current knowledge of these soluble products, how they are generated, their interactions, roles, and their potential use as biomarkers in prognosis and treatment related to inflammatory, cardiovascular, and autoimmune diseases.

Sox7 is involved in antibody-dependent endothelial cell activation and renal allograft injury via the Jagged1-Notch1 pathway

BACKGROUND

Antibody-mediated rejection (AMR) can cause graft loss and reduces long-term graft survival after kidney transplantation. Human leukocyte antigen (HLA) and/or non-HLA antibodies play a key role in the pathogenesis of AMR by targeting the allograft epithelium via complement activation and complement-independent mechanisms. However, the precise mechanisms of AMR remain unclear and treatment is still limited.

METHODS

In this study, we investigated the role of the endothelial-associated transcription factor Sox7 in AMR, using the anti-HLA antibody W6/32, shRNA-mediated Sox7 knockdown, and by manipulating the Notch pathway. We used an in vitro human kidney glomerular endothelial cells (HKGECs) model and an in vivo MHC-mismatched kidney transplantation model.

RESULTS

Sox7 expression was upregulated and the Jagged1-Notch1 pathway was activated in HKGECs after W6/32 activation. W6/32 antibodies increased the expression of adhesion molecules (VCAM-1, ICAM-1), inflammatory cytokines (IL-6, TNF-α), and chemokines (CXCL8, CXCL10), and Sox7 knockdown and inhibition of the Notch pathway by DAPT significantly reduced these effects. Jagged1 overexpression rescued the inhibitory effects of Sox7 knockdown. In addition, Sox7 knockdown attenuated acute allograft kidney injury in mice and reduced the expression of adhesion molecules and Jagged1-Notch1 signaling after transplantation.

CONCLUSIONS

Our findings suggest that Sox7 plays an important role in mediating HLA I antibody-dependent endothelial cell activation and acute kidney allograft rejection via the Jagged1-Notch1 pathway. Manipulating Sox7 in donor organs may represent a useful treatment for AMR in solid organ transplantation.

Structural Immunology of Complement Receptors 3 and 4

Complement receptors (CR) 3 and 4 belong to the family of beta-2 (CD18) integrins. CR3 and CR4 are often co-expressed in the myeloid subsets of leukocytes, but they are also found in NK cells and activated T and B lymphocytes. The heterodimeric ectodomain undergoes considerable conformational change in order to switch the receptor from a structurally bent, ligand-binding in-active state into an extended, ligand-binding active state. CR3 binds the C3d fragment of C3 in a way permitting CR2 also to bind concomitantly. This enables a hand-over of complement-opsonized antigens from the cell surface of CR3-expressing macrophages to the CR2-expressing B lymphocytes, in consequence acting as an antigen presentation mechanism. As a more enigmatic part of their functions, both CR3 and CR4 bind several structurally unrelated proteins, engineered peptides, and glycosaminoglycans. No consensus motif in the proteinaceous ligands has been established. Yet, the experimental evidence clearly suggest that the ligands are primarily, if not entirely, recognized by a single site within the receptors, namely the metal-ion dependent adhesion site (MIDAS). Comparison of some recent identified ligands points to CR3 as inclined to bind positively charged species, while CR4, by contrast, binds strongly negative-charged species, in both cases with the critical involvement of deprotonated, acidic groups as ligands for the Mg²⁺ ion in the MIDAS. These properties place CR3 and CR4 firmly within the realm of modern molecular medicine in several ways. The expression of CR3 and CR4 in NK cells was recently demonstrated to enable complement-dependent cell cytotoxicity toward antibody-coated cancer cells as part of biological therapy, constituting a significant part of the efficacy of such treatment. With the flexible principles of ligand recognition, it is also possible to propose a response of CR3 and CR4 to existing medicines thereby opening a possibility of drug repurposing to influence the function of these receptors. Here, from advances in the structural and cellular immunology of CR3 and CR4, we review insights on their biochemistry and functions in the immune system.

Decreased monocyte shedding of the migration inhibitor soluble CD18 in alcoholic hepatitis

OBJECTIVES

During alcoholic hepatitis (AH) monocytes traverse the vascular boundaries and massively invade the liver. In principle, tissue extravasation can be limited through shedding of CD18 integrins from leukocytes, including monocytes. The soluble (s) product sCD18 conceals adhesion receptors on the endothelium, which reduces monocyte extravasation. In AH, monocytes are dysfunctional, but whether this involves their self-generated anti-migration is unknown. Our aim was, therefore, to investigate monocyte CD18 dynamics in AH.

METHODS

We studied 50 AH patients and 20 healthy controls. We measured monocyte expression and conformational activation of CD18, plasma (P)-sCD18, stimulated in vitro CD18 shedding and P-sCD18 in a short-term chronic-binge mouse model.

RESULTS

AH-derived monocytes had a 30-60% higher expression of active CD18 receptors (p < 0.01), but the sCD18 concentration per monocyte was reduced in vivo by 30% and in vitro by 120% (p < 0.01). Ethanol reduced the in vitro shedding of CD18 in the patients only. TNFα increased sCD18 concentration per monocyte, but less so in the patients (p < 0.04). P-sCD18 per monocyte was inversely related to disease severity. In early alcoholic liver disease, P-sCD18 was decreased in the mouse model.

CONCLUSIONS

The monocyte CD18 integrins are highly activated in AH and the single monocyte shedding of CD18 was decreased favoring tissue extravasation. Alcohol in itself and altered monocyte responsiveness to TNFα may explain this lowered shedding.

TRANSLATIONAL IMPACT

The contribution of this mechanism to the excessive monocyte liver infiltration in AH should be further explored as it may serve as a potential therapeutic target to limit liver inflammation.

Altered levels of soluble CD18 may associate immune mechanisms with outcome in sepsis

The pathogenesis of sepsis involves a dual inflammatory response, with a hyperinflammatory phase followed by, or in combination with, a hypoinflammatory phase. The adhesion molecules lymphocyte function-associated antigen (LFA-1) (CD11a/CD18) and macrophage-1 (Mac-1) (CD11b/CD18) support leucocyte adhesion to intercellular adhesion molecules and phagocytosis through complement opsonization, both processes relevant to the immune response during sepsis. Here, we investigate the role of soluble (s)CD18 in sepsis with emphasis on sCD18 as a mechanistic biomarker of immune reactions and outcome of sepsis. sCD18 levels were measured in 15 septic and 15 critically ill non-septic patients. Fifteen healthy volunteers served as controls. CD18 shedding from human mononuclear cells was increased in vitro by several proinflammatory mediators relevant in sepsis. sCD18 inhibited cell adhesion to the complement fragment iC3b, which is a ligand for CD11b/CD18, also known as Mac-1 or complement receptor 3. Serum sCD18 levels in sepsis non-survivors displayed two distinct peaks permitting a partitioning into two groups, namely sCD18 'high' and sCD18 'low', with median levels of sCD18 at 2158 mU/ml [interquartile range (IQR) 2093-2811 mU/ml] and 488 mU/ml (IQR 360-617 mU/ml), respectively, at the day of intensive care unit admission. Serum sCD18 levels partitioned sepsis non-survivors into one group of 'high' sCD18 and low CRP and another group with 'low' sCD18 and high C-reactive protein. Together with the mechanistic data generated in vitro, we suggest the partitioning in sCD18 to reflect a compensatory anti-inflammatory response syndrome and hyperinflammation, respectively, manifested as part of sepsis.

Changes in Soluble CD18 in Murine Autoimmune Arthritis and Rheumatoid Arthritis Reflect Disease Establishment and Treatment Response

INTRODUCTION

In rheumatoid arthritis (RA) immune activation and presence of autoantibodies may precede clinical onset of disease, and joint destruction can progress despite remission. However, the underlying temporal changes of such immune system abnormalities in the inflammatory response during treat-to-target strategies remain poorly understood. We have previously reported low levels of the soluble form of CD18 (sCD18) in plasma from patients with chronic RA and spondyloarthritis. Here, we study the changes of sCD18 before and during treatment of early RA and following arthritis induction in murine models of rheumatoid arthritis.

METHODS

The level of sCD18 was analyzed with a time-resolved immunoflourometric assay in 1) plasma from early treatment naïve RA patients during a treat-to-target strategy (the OPERA cohort), 2) plasma from chronic RA patients, 3) serum from SKG and CIA mice following arthritis induction, and 4) supernatants from synovial fluid mononuclear cells (SFMCs) and peripheral blood mononuclear cells (PBMCs) from 6 RA patients cultured with TNFα or adalimumab.

RESULTS

Plasma levels of sCD18 were decreased in chronic RA patients compared with early RA patients and in early RA patients compared with healthy controls. After 12 months of treatment the levels in early RA patients were similar to healthy controls. This normalization of plasma sCD18 levels was more pronounced in patients with very early disease who achieved an early ACR response. Plasma sCD18 levels were associated with radiographic progression. Correspondingly, the serum level of sCD18 was decreased in SKG mice 6 weeks after arthritis induction compared with healthy littermates. The sCD18 levels in both SKG and CIA mice exhibited a biphasic course after arthritis induction with an initial increase above baseline followed by a decline. Shedding of CD18 from RA SFMC and RA PBMC cultures was increased by TNFα and decreased by adalimumab.

CONCLUSIONS

The plasma sCD18 levels were altered in patients with RA, in mice with autoimmune arthritis and in cell cultures treated with TNFα and adalimumab. Decreased levels of plasma sCD18 could reflect autoimmunity in transition from early to chronic disease and normalization in response to treatment could reflect autoimmunity in remission.

Interleukin 20 regulates dendritic cell migration and expression of co-stimulatory molecules

Background

Psoriasis is an inflammatory disease characterized by leukocyte skin infiltration. Interestingly, recent works suggest that the migration of dendritic cells (DCs) is abnormal in psoriatic skin. DCs have significant role in regulating the function of T lymphocytes, at least in part influenced by the local environment of cytokines. In psoriatic skin lesions the expression of IL-20 is highly up-regulated. It is unclear if this cytokine has any influence on DCs.

Methods

Here, we investigated the influence of IL-20 in monocyte-derived dendritic cell (MDDCs) in vitro. This work addressed IL-20 effects on DC maturation, receptor expression and signaling. By use of extra cellular matrix components mimicking the skin environment, we also studied the functional effects of IL-20 on the chemotactic migration of DCs. Based on the recent finding that CD18 integrin are shed during migration of myeloid leukocytes, the concentration of these adhesion molecules was measured in MDDCs culture supernatants post migration.

Results

Following stimulation with IL-20, immature human MDDCs enhanced the expression of the co-stimulatory molecule CD86, further enabling activation of the p38 MAPK, but not the STAT3, pathway. IL-20 increased the migration of MDDCs in a biphasic response narrowly controlled by the interleukin concentration. A concomitant change in the shedding of CD18 integrins suggested that these adhesion molecules play a role in the migration of the MDDCs through the extracellular matrix layer.

Conclusion

Taken together, our findings points to a possible, yet subtle, role of IL-20 in DCs migration. The biphasic response suggests that the aberrant IL-20 expression in psoriasis impedes DC migration, which could be a part of the processes that precipitates the dysregulated inflammatory response associated with this disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s40591-016-0046-x) contains supplementary material, which is available to authorized users.

Interleukin 20 regulates dendritic cell migration and expression of co-stimulatory molecules

BACKGROUND

Psoriasis is an inflammatory disease characterized by leukocyte skin infiltration. Interestingly, recent works suggest that the migration of dendritic cells (DCs) is abnormal in psoriatic skin. DCs have significant role in regulating the function of T lymphocytes, at least in part influenced by the local environment of cytokines. In psoriatic skin lesions the expression of IL-20 is highly up-regulated. It is unclear if this cytokine has any influence on DCs.

METHODS

Here, we investigated the influence of IL-20 in monocyte-derived dendritic cell (MDDCs) in vitro. This work addressed IL-20 effects on DC maturation, receptor expression and signaling. By use of extra cellular matrix components mimicking the skin environment, we also studied the functional effects of IL-20 on the chemotactic migration of DCs. Based on the recent finding that CD18 integrin are shed during migration of myeloid leukocytes, the concentration of these adhesion molecules was measured in MDDCs culture supernatants post migration.

RESULTS

Following stimulation with IL-20, immature human MDDCs enhanced the expression of the co-stimulatory molecule CD86, further enabling activation of the p38 MAPK, but not the STAT3, pathway. IL-20 increased the migration of MDDCs in a biphasic response narrowly controlled by the interleukin concentration. A concomitant change in the shedding of CD18 integrins suggested that these adhesion molecules play a role in the migration of the MDDCs through the extracellular matrix layer.

CONCLUSION

Taken together, our findings points to a possible, yet subtle, role of IL-20 in DCs migration. The biphasic response suggests that the aberrant IL-20 expression in psoriasis impedes DC migration, which could be a part of the processes that precipitates the dysregulated inflammatory response associated with this disease.

CD11a, CD11c, and CD18 gene polymorphisms and susceptibility to Behçet's disease in Koreans

Lesions of Behçet's disease (BD) show vascular infiltrates of immune cells expressing integrins. β2 integrins (CD11/CD18) play a major role in cell migration to the inflammatory lesion and also induce cytokine production. Thus, genetic polymorphisms of CD11/CD18 may be associated with the pathogenesis of BD. In this study, nine single nucleotide polymorphisms (SNPs) of the CD11a, CD11c, and CD18 were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and haplotype analysis in 305 BD patients and 266 healthy controls. The frequencies of genotype rs11574944 CC and haplotype rs11574944C-rs2230433G-rs8058823A in CD11a were significantly lower in BD patients. The frequencies of genotype rs2230429 CC, rs2929 GG, and haplotype rs2230429C-rs2929G in CD11c were higher in BD patients. The frequencies of genotype rs235326CC and haplotype rs2070946A-rs235326C-rs760456G-rs684G in CD18 were significantly higher in the BD patients than in the controls. Other SNPs in CD11a, CD11c, and CD18 gene were not significantly different. Therefore, the major genotype and haplotype of CD11a/CD18 may play a role in decreasing the susceptibility of BD, whereas the major genotype and haplotype of CD11c/CD18 may play a role in increasing the susceptibility of BD.

Sialic acid residues are essential for cell lysis mediated by leukotoxin from Aggregatibacter actinomycetemcomitans

Leukotoxin (LtxA) from Aggregatibacter actinomycetemcomitans is known to target and lyse β2-integrin-expressing cells such as polymorphonuclear leukocytes and macrophages. LtxA is an important virulence factor that facilitates chronic inflammation and is strongly associated with a fast-progressing form of periodontitis caused by the JP2 clone of the bacterium. Here, we show that sialic acid residues are important for LtxA-induced cell lysis, regardless of whether the cell express β2-integrin or not. Clearly, removal of sialic acid groups significantly reduces a β2-integrin-specific LtxA-induced lysis. Moreover, sialic acid presented on alternative proteins, such as, for instance, on erythrocytes that do not express β2-integrin, also makes the cells more sensitive to LtxA. The data also illustrate the importance of the negative charge in order for the sialic acid to associate LtxA with the membrane. Removal of sialic acid is in itself sufficient to significantly reduce the negative charge on the erythrocytes. Moreover, we found that on human erythrocytes there is a positive association between the sensitivity to LtxA and the amount of negative charge caused by sialic acid. Interestingly, these features are not shared by all RTX toxins, since α-hemolysin from Escherichia coli induced cell lysis of both β2-integrin-expressing and nonexpressing cells and this lysis is independent of the presence of sialic acid residues. In conclusion, LtxA not only is cytotoxic to β2-integrin-expressing cells but can potentially initiate cell lysis in all cells that present a sufficient density of sialic acid groups on their plasma membrane.

Decreased plasma levels of soluble CD18 link leukocyte infiltration with disease activity in spondyloarthritis

INTRODUCTION

Spondyloarthritis (SpA) comprises a group of diseases often associated with HLA-B27 and characterized by inflammation of the entheses and joints of the axial skeleton. The inflammatory process in SpA is presumably driven by innate immune cells but is still poorly understood. Thus, new tools for monitoring and treating inflammation are needed. The family of CD18 integrins is pivotal in guiding leukocytes to sites of inflammation, and CD18 hypomorphic mice develop a disease resembling SpA. Previously, we demonstrated that altered soluble CD18 (sCD18) complexes in the blood and synovial fluid of patients with arthritis have anti-inflammatory functions. Here, we study the mechanisms for these alterations and their association with SpA disease activity.

METHODS

Plasma levels of sCD18 in a study population with 84 patients with SpA and matched healthy controls were analyzed with a time-resolved immunoflourometric assay (TRIFMA). Binding of sCD18 to endothelial cells and fibroblast-like synoviocytes (FLSs) was studied with confocal microscopy. Shedding of CD18 from peripheral blood mononuclear cells (PBMCs) was studied with flow cytometry and TRIFMA.

RESULTS

Plasma levels of sCD18 were decreased in patients with SpA compared with healthy volunteers (P <0.001), and the lowest levels were in the HLA-B27-positive subgroup (P <0.05). In a multiple regression model, the sCD18 levels exhibited an inverse correlation with the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) (P <0.05), the level of morning stiffness (P <0.05), the Bath Ankylosing Spondilitis Metrology Index (P <0.05), the physician global assessment score (P <0.01), and the sacroiliac magnetic resonance imaging activity score (P <0.05). The mechanisms for these changes could be simulated in vitro. First, sCD18 in plasma adhered to inflammation-induced intercellular adhesion molecule 1 (ICAM-1) on endothelial cells and FLS, indicating increased consumption. Second, CD18 shedding from SpA PBMCs correlated inversely with the BASDAI (P <0.05), suggesting insufficient generation. CD18 was shed primarily from intermediate CD14⁺⁺ CD16⁺ monocytes, supporting the view that alterations in innate immunity can regulate the inflammatory processes in SpA.

CONCLUSIONS

Taken together, the failure of patients with SpA to maintain adequate sCD18 levels may reflect insufficient CD18 shedding from monocytes to counterbalance the capture of sCD18 complexes to inflammation-induced ICAM-1. This could increase the availability of ICAM-1 molecules on the endothelium and in the synovium, facilitating leukocyte migration to the entheses and joints and aggregating disease activity.

Detection of soluble CR3 (CD11b/CD18) by time-resolved immunofluorometry

In the cell membrane complement receptor 3 (CR3) consists of one alpha chain (CD11b) and one beta chain (CD18). CR3 participates in many immunological processes, especially those involving cell migration, adhesion, and phagocytosis of complement-opsonized microbes. Recent findings of soluble CR3 in body fluids and in culture supernatant from experiments in vitro point to the involvement of ecto domain shedding as a part of the CR3 biology. To monitor such shedding on a quantitative basis, we have developed time-resolved immunofluorometric assays (TRIFMA) to detect soluble CD11b and CD18 in plasma or serum of either human or murine origin. Compared with most enzyme-linked immunosorbent assays methodologies, TRIFMA possesses prominent advantages, including better dynamic range and reproducibility. These assays may contribute to the understanding of the role of shedding of CR3 and other cell adhesion molecules in human disease and animal models involving inflammation.

Interleukin (IL)-4 induces production of cytokine-induced neutrophil chemoattractants (CINCs) and intercellular adhesion molecule (ICAM)-1 in lungs of asthmatic rats

The present study aimed to examine the effect of interleukin (IL)-4 on neutrophil chemotaxis in airway inflammation in asthmatic rats and the possible mechanism. Male Wistar rats were intranasally instilled with recombinant rat (rr) IL-4 (rrIL-4) at different doses [2, 4 or 8 μg/animal, dissolved in 200 μL normal saline (NS)] or rrIL-4 at 4 μg/animal (dissolved in 200 μL NS). NS (200 μL) and LPS (6 mg/kg/animal, dissolved in 200 μL NS) were intranasally given respectively in the negative and positive control groups. Moreover, the asthmatic lung inflammation was induced in rats which were then intranasally treated with rrIL-4 (4 μg/animal) or LPS (6 mg/kg/animal). The normal rats treated with different doses of rrIL-4 and those asthmatic rats were sacrificed 6 h later. And animals instilled with rrIL-4 at 4 μg were sacrificed 6, 12 or 24 h later. The bronchoalveolar lavage fluid (BALF) and lungs were harvested for detection of leukocyte counts by Wright-Giemsa staining and lung histopathology by haematoxylin-eosin (HE) staining. The levels of cytokine-induced neutrophil chemoattractant (CINC)-1 and intercellular adhesion molecule (ICAM)-1 in BALF were determined by ELISA. Real-time PCR was used to measure the mRNA expression of CINCs (CINC-1, CINC-2α, CINC-2β, CINC-3) and ICAM-1 in lung tissues. The results showed that the intranasal instillation of IL-4 did not induce a recruitment of neutrophils in BALF in rats. However, IL-4 could increase the CINC-1 level in BALF in a dose-dependent manner at 6 h. But the mRNA expression levels of CINC-1, CINC-2α, CINC-2β, CINC-3 were not significantly increased in lungs of IL-4-treated rats relative to NS negative control group. Moreover, IL-4 was found to augment the mRNA expression of ICAM-1 in lungs and the ICAM-1 level in BALF at 6 h. However, the increase in CINC-1 and ICAM-1 levels in BALF of IL-4-treated asthmatic rats was not significantly different from that in untreated asthmatic rats. These findings indicate that IL-4 does not directly recruit neutrophils in the rat lungs, but it may contribute to airway neutrophilia through up-regulation of CINC-1 and ICAM-1.

A simple set of validation steps identifies and removes false results in a sandwich enzyme-linked immunosorbent assay caused by anti-animal IgG antibodies in plasma from arthritis patients

Rheumatoid arthritis (RA) and spondyloarthritis (SpA) are chronic diseases characterized by activation of the immune system and production of antibodies. Thus, rheumatoid factor, anti-animal IgG antibodies and heterophilic antibodies in plasma samples from arthritis patients can interfere with immunoassays such as sandwich enzyme-linked immunosorbent assay (ELISA) systems often used in arthritis research. However, standard methodologies on how to test for false results caused by these antibodies are lacking. The objective of this study was to design a simple set of steps to validate a sandwich ELISA before using it for measuring analytes in plasma from arthritis patients. An interleukin-24 (IL-24) sandwich ELISA system was prepared with a monoclonal mouse capture antibody and a polyclonal goat detection antibody and tested for interference by rheumatoid factor, anti-animal IgG antibodies and heterophilic antibodies. Plasma samples from 23 patients with RA and SpA were used. No differences were found between plasma samples measured in wells coated with anti-IL-24 specific antibody and in wells coated with isotype control antibody (false positive results), and recombinant human IL-24 was not recovered in spiked samples (false negative results). This interference was removed after preincubating the plasma samples from patients with arthritis with goat or bovine IgG, suggesting that anti-animal IgG antibodies found in the plasma of the arthritis patients caused the false results. Additional testing showed that the signal-to-noise ratio could be increased by titration of the capture and detection antibodies and by using the ELAST amplification system. Finally, the calculated concentration of IL-24 was increased in ethylenediaminetetraacetic acid (EDTA) plasma compared to heparin plasma and serum and decreased with repetitive freeze/thaw cycles of the samples illustrating how sample handling could additionally contribute to the variations reported by different laboratories in measurement of the same analyte. This study proposes a simple set of validation steps to evaluate and optimize a sandwich ELISA before using it for measuring analytes in plasma from arthritis patients. Anti-animal IgG antibodies are also present in healthy individuals, suggesting that validation of ELISA systems for measuring non-arthritis samples could also be improved by this simple set of validation steps.

Monodisperse and LPS-free Aggregatibacter actinomycetemcomitans leukotoxin: interactions with human β2 integrins and erythrocytes

Aggregatibacter actinomycetemcomitans is a gram-negative, facultatively anaerobic cocco-bacillus and a frequent member of the human oral flora. It produces a leukotoxin, LtxA, belonging to the repeats-in-toxin (RTX) family of bacterial cytotoxins. LtxA efficiently kills neutrophils and mononuclear phagocytes. The known receptor for LtxA on leukocytes is integrin α(L)β(2) (LFA-1 or CD11a/CD18). However, the molecular mechanisms involved in LtxA-mediated cytotoxicity are poorly understood, partly because LtxA has proven difficult to prepare for experiments as free of contaminants and with its native structure. Here, we describe a protocol for the purification of LtxA from bacterial culture supernatant, which does not involve denaturing procedures. The purified LtxA was monodisperse, well folded as judged by the combined use of synchrotron radiation circular dichroism spectroscopy (SRCD) and in silico prediction of the secondary structure content, and free of bacterial lipopolysaccharide. The analysis by SRCD and similarity to a lipase from Pseudomonas with a known three dimensional structure supports the presence of a so-called beta-ladder domain in the C-terminal part of LtxA. LtxA rapidly killed K562 target cells transfected to express β(2) integrin. Cells expressing α(M)β(2) (CD11b/CD18) or α(X)β(2) (CD11c/CD18) were killed as efficiently as cells expressing α(L)β(2). Erythrocytes, which do not express β(2) integrins, were lysed more slowly. In ligand blotting experiments, LtxA bound only to the β(2) chain (CD18). These data support a previous suggestion that CD18 harbors the major binding site for LtxA as well as identifies integrins α(M)β(2) and α(X)β(2) as novel receptors for LtxA.

On the roles of polyvalent binding in immune recognition: perspectives in the nanoscience of immunology and the immune response to nanomedicines

Immunology often conveys the image of large molecules, either in the soluble state or in the membrane of leukocytes, forming multiple contacts with a target for actions of the immune system. Avidity names the ability of a polyvalent molecule to form multiple connections of the same kind with ligands tethered to the same surface. Polyvalent interactions are vastly stronger than their monovalent equivalent. In the present review, the functional consequences of polyvalent interactions are explored in a perspective of recent theoretical advances in understanding the thermodynamics of such binding. From insights on the structural biology of soluble pattern recognition molecules as well as adhesion molecules in the cell membranes or in their proteolytically shed form, this review documents the prominent role of polyvalent interactions in making the immune system a formidable barrier to microbial infection as well as constituting a significant challenge to the application of nanomedicines.

Glatiramer acetate in treatment of multiple sclerosis: a toolbox of random co-polymers for targeting inflammatory mechanisms of both the innate and adaptive immune system?

Multiple sclerosis is a disease of the central nervous system, resulting in the demyelination of neurons, causing mild to severe symptoms. Several anti-inflammatory treatments now play a significant role in ameliorating the disease. Glatiramer acetate (GA) is a formulation of random polypeptide copolymers for the treatment of relapsing-remitting MS by limiting the frequency of attacks. While evidence suggests the influence of GA on inflammatory responses, the targeted molecular mechanisms remain poorly understood. Here, we review the multiple pharmacological modes-of-actions of glatiramer acetate in treatment of multiple sclerosis. We discuss in particular a newly discovered interaction between the leukocyte-expressed integrin α(M)β(2) (also called Mac-1, complement receptor 3, or CD11b/CD18) and perspectives on the GA co-polymers as an influence on the function of the innate immune system.

The role of higher-order protein structure in supporting binding by heteroclitic monoclonal antibodies: the monoclonal antibody KIM185 to CD18 also binds C4-binding protein

Heteroclitic monoclonal antibodies are characterized by the ability to bind multiple epitopes with little or no similarity. Such antibodies have been reported earlier, but insight into to the molecular basis of this propensity is limited. Here we report that the KIM185 antibody to human CD18 reacts with the plasma protein C4b-binding protein (C4BP). This was revealed during affinity purification procedures where human serum was incubated with surfaces coated with monoclonal antibodies to CD18. Other monoclonal antibodies to CD18 (KIM127 and TS1/18) showed no such interaction with C4BP. We constructed a sandwich-type time-resolved immunofluorometric assay using KIM185 both as capture and developing antibody. By use of proteolytic fragments of KIM185 and recombinant deletion mutants of C4BP the interaction sites were mapped to the variable region of KIM185 and the oligomerization domain of C4BP, respectively. C4BP is a large oligomeric plasma protein that binds activated complement factor C4b and other endogenous ligands as well as microorganisms. By use of the recent crystallographic data on the structure of CD11c/CD18 and prediction of the secondary structure of the C4BP oligomerization domain, we show that epitopes bound by KIM185 in these proteins are unlikely to share any major structural similarity. However, both antigens may form oligomers that would enable avid binding by the antibody. Our report points to the astonishing ability of heteroclitic antibodies to accommodate the binding of multiple proteins with no or little structural similarity within the confined space of the variable regions.

Metalloproteinase-mediated Shedding of Integrin β2 promotes macrophage efflux from inflammatory sites

Macrophage exiting from inflammatory sites is critical to limit the local innate immune response. With tissue insult, resident tissue macrophages rapidly efflux to lymph nodes where they modulate the adaptive immune response, and inflammatory macrophages attracted to the site of injury then exit during the resolution phase. However, the mechanisms that regulate macrophage efflux are poorly understood. This study has investigated soluble forms of integrin β2 whose levels are elevated in experimental peritonitis at times when macrophages are exiting the peritoneum, suggesting that its proteolytic shedding may be involved in macrophage efflux. Both constitutive and inducible metalloproteinase-dependent shedding of integrin β2 from mouse macrophages are demonstrated. Soluble integrin β2 is primarily released as a heterodimeric complex with αM that retains its ability to bind its ligands intracellular adhesion molecule-1, fibrin, and collagen and thus may serve as a soluble antagonist. In a model of accelerated exiting, administration of a metalloproteinase inhibitor prevents macrophage efflux by 50% and impedes loss of macrophage integrin β2 from the cell surface. Exiting of peritoneal macrophages in mice lacking integrin β2 is accelerated, and antibody disruption of integrin β2-substrate interactions can reverse 50% of the metalloprotease inhibitor blockade of macrophage exiting. Thus, our study demonstrates the ability of metalloproteinase-mediated shedding of integrin β2 to promote macrophage efflux from inflammatory sites, and the release of soluble integrin heterodimers may also limit local inflammation.

MMP9 cleavage of the β4 integrin ectodomain leads to recurrent epithelial erosions in mice

Integrin α6β4 is an integral membrane protein within hemidesmosomes and it mediates adhesion of epithelial cells to their underlying basement membrane. During wound healing, disassembly of hemidesmosomes must occur for sheet movement-mediated cell migration. The mechanisms of disassembly and reassembly of hemidesmosomes are not fully understood. The current study was initiated to understand the underlying cause of recurrent corneal erosions in the mouse. Here, we show that in vivo: (1) MMP9 levels are elevated and β4 integrin is partially cleaved in epithelial cell extracts derived from debridement wounded corneas; (2) the β4 ectodomain is missing from sites where erosions develop; and (3) β4 cleavage can be reduced by inhibiting MMP activity. Although β4, α3 and β1 integrins were all cleaved by several MMPs, only MMP9 was elevated in cell extracts derived from corneas with erosions. Coimmunoprecipitation studies showed that β4 integrin associates with MMP9, and protein clustering during immunoprecipitation induced proteolytic cleavage of the β4 integrin extracellular domain, generating a 100 kDa β4 integrin cytoplasmic domain fragment. Confocal imaging with three-dimensional reconstruction showed that MMP9 localizes at erosion sites in vivo where the ectodomain of β4 integrin is reduced or absent. MMP activation experiments using cultured corneal and epidermal keratinocytes showed reduced levels of α6β4 and β1 integrins within 20 minutes of phorbol ester treatment. This report is the first to show that β4 integrin associates with MMP9 and that its ectodomain is a target for cleavage by MMP9 in vivo under pathological conditions.