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

Tumor necrosis factor alpha neutralization attenuates immune checkpoint inhibitor-induced activation of intermediate monocytes in synovial fluid mononuclear cells from patients with inflammatory arthritis

Objective

During treatment with immune checkpoint inhibitors (ICI) such as the anti-PD-1 antibody pembrolizumab, half of patients with pre-existing inflammatory arthritis experience disease flares. The underlying immunological mechanisms have not been characterized. Here, we investigate the effect of pembrolizumab on cells involved in inflammation and destruction in the synovial joint and how immunosuppressive treatments affect the pembrolizumab-induced immune reactions.

Methods

We included synovial fluid mononuclear cells (SFMCs, n = 28) and peripheral blood mononuclear cells (PBMCs, n = 6) from patients with rheumatoid arthritis and peripheral spondyloarthritis and PBMCs from healthy controls (n = 6). Fibroblast-like synovial cells (FLSs) were grown from SFMCs. The in vitro effect of pembrolizumab was tested in SFMCs cultured for 48 h, FLS-PBMC co-cultures and in SFMCs cultured for 21 days (inflammatory osteoclastogenesis). Cells and supernatants were analyzed by ELISA, flow cytometry, and pro-inflammatory multiplex assay. Finally, the effect of the disease-modifying anti-rheumatic drugs (DMARDs) adalimumab (TNFα inhibitor), tocilizumab (IL-6R inhibitor), tofacitinib (JAK1/JAK3 inhibitor), and baricitinib (JAK1/JAK2 inhibitor) on pembrolizumab-induced immune reactions was tested.

Results

Pembrolizumab significantly increased monocyte chemoattractant protein-1 (MCP-1) production by arthritis SFMCs (P = 0.0031) but not by PBMCs from patients or healthy controls (P = 0.77 and P = 0.43). Pembrolizumab did not alter MMP-3 production in FLS-PBMC co-cultures (P = 0.76) or TRAP secretion in the inflammatory osteoclastogenesis model (P = 0.28). In SFMCs, pembrolizumab further increased the production of TNFα (P = 0.0110), IFNγ (P = 0.0125), IL-12p70 (P = 0.0014), IL-10 (P = 0.0100), IL-13 (P = 0.0044), IL-2 (P = 0.0066), and IL-4 (P = 0.0008) but did not change the production of IL-6 (P = 0.1938) and IL-1 (P = 0.1022). The SFMCs treated with pembrolizumab showed an increased frequency of intermediate monocytes (P = 0.044), and the MCP-1 production increased only within the intermediate monocyte subset (P = 0.028). Lastly, adalimumab, baricitinib, and tofacitinib treatment were able to attenuate the pembrolizumab-induced MCP-1 production (P = 0.0004, P = 0.033, and P = 0.025, respectively), while this was not seen with tocilizumab treatment (P = 0.75).

Conclusion

Pembrolizumab specifically activated intermediate monocytes and induced the production of several cytokines including TNFα but not IL-6. These findings indicate that flares in patients with pre-existing inflammatory arthritis involve monocyte activation and could be managed with TNFα neutralization.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02737-6.

Responses to Cytokine Inhibitors Associated with Cellular Composition in Models of Immune-Mediated Inflammatory Arthritis

Objective

Immune‐mediated inflammatory arthritis (IMIA) is a heterogeneous group of diseases including rheumatoid arthritis (RA), psoriatic arthritis (PsA), and spondyloarthritis (SpA). Disease‐modifying antirheumatic drugs (DMARDs) target very different cellular components of the disease processes. Characterization of the pathobiological subtypes of IMIA could provide more specific treatment approaches for each disease. For example, RA has been proposed to consist of at least three synovial pathotypes (lymphoid, myeloid, and fibroid), and only a subgroup of RA patients have erosive disease. The objective of this study was to evaluate the effects of various DMARDs on different synovial cell subsets using human ex vivo models of IMIA.

Methods

Synovial fluid and blood samples were obtained from a study population consisting of patients with RA, PsA, or peripheral SpA with at least one swollen joint (n = 18). The DMARDs used in this study were methotrexate, adalimumab, etanercept, tocilizumab, anakinra, ustekinumab, secukinumab, tofacitinib, and baricitinib. Paired synovial fluid mononuclear cells (SFMCs), peripheral blood mononuclear cells (PBMCs), and fibroblast‐like synovial cells (FLSs) were used in three different previously optimized ex vivo models.

Results

In SFMCs cultured for 48 hours, all DMARDs except anakinra decreased the production of monocyte chemoattractant protein (MCP)‐1. In SFMCs cultured for 21 days, only the two tumor necrosis factor alpha (TNFα) inhibitors adalimumab and etanercept decreased the secretion of tartrate‐resistant acid phosphatase (P < 0.01, P < 0.001). In the FLS and PBMC 48‐hour co‐cultures, only tocilizumab (P < 0.001) and the two Janus kinase inhibitors tofacitinib and baricitinib (both P < 0.05) decreased the production of MCP‐1 by around 50%.

Conclusion

TNFα inhibition was effective in preventing inflammatory osteoclastogenesis, whereas tocilizumab, tofacitinib, and baricitinib had superior efficacy in cultures dominated by FLSs. Taken together, this study reveals that responses to cytokine inhibitors associate with cellular composition in models of IMIA. In particular, this study provides new evidence on the differential effect of DMARDs on leukocytes compared with stromal cells.

Rheumatoid arthritis mediator CD18 expression by Staphylococcus aureus superantigen C in rats

BACKGROUND AND OBJECTIVES

Microbial superantigens have been reported in the blood and synovial fluid of rheumatoid arthritis patients, raising the question of whether the presence of these superantigens could provoke the induction of inflammatory biomarkers expression or not. The purpose of this study was to examine the Staphylococcus aureus superantigen C on CD18 expression.

MATERIALS AND METHODS

The superantigen C was purified by ultrafiltration. Immunoblotting was performed using a specific antibody. Also, 50 micrograms of superantigens (toxin) were injected intraperitoneally and intra-articularly into separate rat groups. Blood was collected and RNA extracted. Then, the cDNA was synthesized. The expression of CD18 marker was evaluated using RT-real-time PCR, and the results were descriptively analyzed.

RESULTS

The results of this study revealed that 50 μg of toxin, injected intra-articularly and intraperitoneally, showed the surplus expression of the marker CD18 in the blood of rats after 20 days. By this method, the expression of the marker CD18 was significantly different between rats that received the superantigen intra-articularly and intraperitoneally (2.10; 2.3 and 3.3 folds) and the controls (P≤ 0.05).

CONCLUSION

The results indicated that the presence of Staphylococcal of superantigen C in the body of rats has enhanced the expression of the CD18 inflammatory marker more than 3 times. This valuable finding is an introduction to further research and could provide new methods to prevent and control inflammatory diseases, including rheumatoid arthritis.

IL-12/IL-23p40 identified as a downstream target of apremilast in ex vivo models of arthritis

BACKGROUND

Apremilast (Otezla®) is a phosphodiesterase 4 (PDE4) inhibitor approved for the treatment of psoriasis and psoriatic arthritis (PsA), but the reason why apremilast shows clinical effect is not fully understood. The objective of this study was to study the downstream effects of apremilast on cells of inflamed joints in immune-mediated inflammatory arthritis.

METHODS

Synovial fluid was obtained from patients with active rheumatoid arthritis (RA), PsA or peripheral spondyloarthritis (SpA; n = 18). The in vitro models consisted of synovial fluid mononuclear cells (SFMCs) or fibroblast-like synovial cells (FLSs) cultured for 48 h, SFMCs cultured for 21 days, an osteoclast pit formation assay, and a mineralization assay.

RESULTS

In SFMCs cultured for 48 h, apremilast decreased the production of interleukin (IL)-12/IL-23p40 (the shared subunit of IL-12 and IL-23), colony-stimulating factor 1, CD6, and CD40 and increased the production of C-X-C motif chemokine 5 dose-dependently. Apremilast had a very different response signature compared with the tumor necrosis factor alpha inhibitor adalimumab with a substantially greater inhibition of IL-12/IL-23p40. In SFMCs cultured for 21 days, apremilast increased the secretion of IL-10. In FLS cultures, apremilast decreased matrix metalloproteinase-3 production. Apremilast decreased osteoclastogenesis but did not affect mineralization by human osteoblasts.

CONCLUSION

This study reveals the downstream effects of apremilast in ex vivo models of arthritis with a strong inhibition of IL-12/IL-23p40 by SFMCs. Our findings could explain some of the efficacy of apremilast seen in IL-12/IL-23-driven immune-mediated inflammatory diseases such as psoriasis and PsA.

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.

Therapeutic effect of the natural compounds baicalein and baicalin on autoimmune diseases

A series of natural compounds have been implicated to be useful in regulating the pathogenesis of various autoimmune diseases. The present study demonstrated that the Scutellariae radix compounds baicalein and baicalin may serve as drugs for the treatment of autoimmune diseases, including rheumatoid arthritis and inflammatory bowel disease. Following the administration of baicalein and baicalin in vivo, T cell‑mediated autoimmune diseases in the mouse model were profoundly ameliorated: In the collagen‑induced arthritis model (CIA), the severity of the disease was reduced by baicalein and, consistently, baicalein was demonstrated to suppress T cell proliferation in CIA mice. In the dextran sodium sulfate (DSS)‑induced colitis model, the disease was attenuated by baicalin, and baicalin promoted colon epithelial cell (CEC) proliferation in vitro. The present study further revealed that the mRNA expression of signal transducer and activator of transcription (STAT)3 and STAT4 in the tyrosine‑protein kinase JAK‑STAT signaling pathway in T cells was downregulated by baicalein, contributing to its regulation of T cell proliferation. However, in the DSS model, the STAT4 transcription in CECs, which are the target cells of activated T cells in the gut, was downregulated by baicalin, suggesting that baicalein and baicalin mediated similar STAT expression in different cell types in autoimmune diseases. In conclusion, the similarly structured compounds baicalein and baicalin selectively exhibited therapeutic effects on autoimmune diseases by regulating cell proliferation and STAT gene expression, albeit in different cell types.

Cytokines and integrins related to inflammation of joint and gut in patients with spondyloarthritis and inflammatory bowel disease

Objectives

Inflammatory bowel disease (IBD) and spondyloarthritis (SpA) have some overlapping clinical features, i.e. gut and joint inflammation. Cytokines of interleukin 17(IL-17)/IL-23 axis play a pathogenic role in both diseases. Integrins (ITGs) regulate migration of immune cells to inflamed tissues (ITGβ7 into gut, ITGβ2 into gut and also to other tissues). In this study, we search for differences in the serum concentrations of these cytokines and integrins between patients suffering from SpA or IBD with and without overlapping symptoms.

Material and methods

Patients with SpA (n = 30), IBD (n = 68), and healthy volunteers (n = 28) were included in the study. Fourteen SpA patients reported symptoms characteristic for IBD. Spondyloarthritis symptoms were diagnosed in 50% of IBD patients, while other patients of this group reported arthralgia only. Serum concentrations of IL-17, IL-22, IL-23, ITGβ2, and ITGβ7 were measured by specific enzyme-linked immunosorbent assay using commercially available sets. The Mann-Whitney and Spearman’s rank tests were used for intergroup comparison and correlation assessment, respectively.

Results

Comparison of patient groups showed significantly higher serum concentrations of IL-17, IL-22, and ITGβ7 in SpA, and up-regulated levels of IL-23 in IBD patients. Similar differences were observed between patient subgroups, both with and without overlapping symptoms. In SpA but not in IBD patients, serum concentrations of ITGβ7 inversely correlated (r = –0.552) with C-reactive protein.

Conclusions

Patients with SpA and IBD differ in the circulating concentrations of IL-17/IL-23 axis cytokines and ITGβ7, irrespectively of the presence or absence of overlapping symptoms. Therefore, we conclude that observed differences are attributed rather to underlying than concurrent disease.

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.