Association of CD163+ macrophages and local production of soluble CD163 with decreased lymphocyte activation in spondylarthropathy synovitis

Efficient intracellular drug-targeting of macrophages using stealth liposomes directed to the hemoglobin scavenger receptor CD163

The hemoglobin scavenger receptor CD163 is exclusively expressed in the monocytic lineage and preferentially in tissue resident macrophages of the M2 phenotype and in macrophages in sites of inflammation and tumor growth. In the present study we have designed liposomes specifically targeting CD163 by hydrophobic linkage of CD163-binding monoclonal antibodies to polyethylene glycol-coated liposomes ('stealth liposomes'). Targeting to the endocytic CD163 protein greatly increased the uptake of liposomes in CD163 transfected cells and macrophages as visualized by confocal microscopy and flow cytometry of cells exposed to CD163 targeting liposomes loaded with calcein. Strong cytotoxic effects were seen in CD163-expressing human monocytes by using the chemotherapeutic agent doxorubicin as cargo of the liposomes. In conclusion, the use of stealth liposomes modified to recognize CD163 is a potential way to target drugs to macrophages that support inflammatory and malignant processes.

CD163 and its expanding functional repertoire

Macrophages are key players of the immune system and express a variety of surface receptors. CD163 is one such receptor which belongs to the scavenger receptor cysteine-rich super family (SRCR-SF) class B. It has four isoforms which differ in the structure of their cytoplasmic domains and putative phosphorylation sites. Expression of CD163 is tightly regulated with a general tendency of anti-inflammatory signals to induce its synthesis, while pro-inflammatory signals downregulate its expression. Previously the molecule has been shown to act as a receptor for hemoglobin-haptoglobin complexes. However, it also plays a crucial role in the control of inflammatory processes by induction of anti-inflammatory pathways. Soluble CD163, which is generated via ectodomain shedding, serves as a potential diagnostic tool in a variety of disease states, such as inflammation, atherosclerosis, transplant rejection and carcinoma. Recently, CD163 has been identified as a promising target for cell directed therapy. In this review we aim to summarize the current knowledge of CD163.

Synovitis in spondyloarthritides

Recent studies using magnetic resonance imaging have suggested that the subchondral bone marrow and the entheses are the sites which are primarily involved in the peripheral and axial inflammation found in patients with spondyloarthritides. Histopathological analyses indicated that the typical morphological features at these sites reflect an inflammation (osteitis) at the bone cartilage interface and in the subchondral bone marrow. This finding implies that synovitis may be of minor importance, especially in comparison to other inflammatory joint diseases such as rheumatoid arthritis. Here, we summarize current available knowledge on synovial involvement in inflammatory processes related to SpA.

Systematic validation of specific phenotypic markers for in vitro polarized human macrophages

BACKGROUND

Polarization of macrophages by specific micro-environmental conditions impacts upon their function following subsequent activation. This study aimed to systematically validate robust phenotypic markers for in vitro polarized human macrophages in order to facilitate the study of macrophage subsets in vivo.

METHODS

Human peripheral blood monocytes were polarized in vitro with IFN-γ, IL-4, or IL-10. Similar experiments were performed with TNF, IL-13, dexamethasone, M-CSF and GM-CSF as polarizing stimuli. Phenotypic markers were assessed by flow cytometry and qPCR.

RESULTS

IFN-γ polarized macrophages (MΦ(IFN-γ)) specifically enhanced membrane expression of CD80 and CD64, IL-4 polarized macrophages (MΦ(IL-4)) mainly upregulated CD200R and CD206, and downregulated CD14 levels, and IL-10 polarized macrophages (MΦ(IL-10)) selectively induced CD163, CD16, and CD32. The expression profiles of the most specific markers were confirmed by qPCR, dose-response experiments, and the use of alternative polarizing factors for each macrophage subset (TNF, IL-13, and dexamethasone, respectively). GM-CSF polarized macrophages (MΦ(GM-CSF)) upregulated CD80 but not CD64 expression, showing a partial phenotypic similarity with MΦ(IFN-γ), and also upregulated the expression of the alternative activation marker CD206. M-CSF polarized macrophages (MΦ(M-CSF)) not only expressed increased levels of CD163 and CD16, resembling MΦ(IL-10,) but also displayed high levels of CD64. The phenotype of MΦ(M-CSF) could be further modulated by additional polarization with IFN-γ, IL-4, or IL-10, whereas MΦ(GM-CSF) showed less phenotypic plasticity.

CONCLUSION

This study validated CD80 as the most robust phenotypic marker for human MΦ(IFN-γ), whereas CD200R was upregulated and CD14 was specifically downregulated on MΦ(IL-4). CD163 and CD16 were found to be specific markers for MΦ(IL-10). The GM-CSF/M-CSF differentiation model showed only a partial phenotypic similarity with the IFN-γ/IL-4/IL-10 induced polarization.

The conserved scavenger receptor cysteine-rich superfamily in therapy and diagnosis

The scavenger receptor cysteine-rich (SRCR) superfamily of soluble or membrane-bound protein receptors is characterized by the presence of one or several repeats of an ancient and highly conserved protein module, the SRCR domain. This superfamily (SRCR-SF) has been in constant and progressive expansion, now up to more than 30 members. The study of these members is attracting growing interest, which parallels that in innate immunity. No unifying function has been described to date for the SRCR domains, this being the result of the limited knowledge still available on the physiology of most members of the SRCR-SF, but also of the sequence versatility of the SRCR domains. Indeed, involvement of SRCR-SF members in quite different functions, such as pathogen recognition, modulation of the immune response, epithelial homeostasis, stem cell biology, and tumor development, have all been described. This has brought to us new information, unveiling the possibility that targeting or supplementing SRCR-SF proteins could result in diagnostic and/or therapeutic benefit for a number of physiologic and pathologic states. Recent research has provided structural and functional insight into these proteins, facilitating the development of means to modulate the activity of SRCR-SF members. Indeed, some of these approaches are already in use, paving the way for a more comprehensive use of SRCR-SF members in the clinic. The present review will illustrate some available evidence on the potential of well known and new members of the SRCR-SF in this regard.

Are current available therapies disease-modifying in spondyloarthritis?

Disease modification in spondyloarthritis should target the improvement of symptoms and preservation of function. Therefore, inhibition of structural damage caused by the disease processes appears essential. In spondyloarthritis, structural damage results mainly in progressive ankylosis of the spine and peripheral joint destruction. Currently available therapies for the treatment of spondyloarthritis appear effective at inhibiting tissue destruction but, with the exception of celecoxib, do not appear to affect new tissue formation leading to ankylosis. In this article, we discuss clinical and pathophysiological concepts of disease modification in spondyloarthritis, challenges in its evaluation, recent clinical data and new concepts that may help explain structural damage as well as the onset and progression of disease.

Comparative assessment of the recognition of domain-specific CD163 monoclonal antibodies in human monocytes explains wide discrepancy in reported levels of cellular surface CD163 expression

BACKGROUND

CD163 is expressed exclusively on cells of the monocyte/macrophage lineage and is widely used as a marker of human macrophages. Further, it has been suggested as a diagnostic marker of monocyte/macrophage activity in inflammatory conditions and as a therapeutic target. However, studies continue to exhibit great discrepancy in the measured percentage of CD163-expressing blood monocytes in healthy individuals. In this study we sought to clarify this inconsistency in reported levels of CD163 surface expression by a detailed analysis of a panel of CD163 antibodies used in previous studies.

MATERIALS AND METHODS

The cellular distribution of CD163 on human peripheral blood monocytes in freshly drawn blood and peripheral blood mononuclear cells isolated from buffy-coats was investigated by flow cytometry using CD163 monoclonal antibodies recognizing scavenger receptor cysteine-rich (SRCR) domain 1 (MAC2-158), domain 4 (R-20), domain 7 (GHI/61), and domain 9 (RM3/1). The CD163 monoclonal antibodies were characterized in binding and endocytosis experiments in human macrophages and CD163-transfected Flp-In CHO cells. Calcium-dependent ligand binding was assessed using surface plasmon resonance, and the specificity of the CD163 monoclonal antibodies was analyzed by western blotting.

RESULTS AND DISCUSSION

Flow cytometric analysis revealed that the estimated proportion of CD163-expressing human peripheral blood monocytes increased when using CD163 monoclonal antibodies recognizing epitopes in the N-terminal part of CD163, remote from the membrane surface. Moreover, the proportion of CD163 positive monocytes observed was highly dependent on free calcium. GHI/61 did not exhibit CD163 binding in the presence of calcium as measured by surface plasmon resonance, which was in agreement with the concordant loss of binding in heparin-stabilized whole blood observed by flow cytometry. In contrast, RM3/1 exhibited weak binding to CD163 in the absence of calcium but high affinity binding to CD163 in the presence of calcium. R-20 and MAC2-158 were unaffected by extracellular calcium levels. The latter SRCR domain 1mAb consistently recognized more than 80% CD163-positive monocytes in human peripheral blood.

CONCLUSION

Epitope accessibility and extracellular calcium dependence elucidate discrepancies in reported levels of monocytic CD163 expression. Utilizing monoclonal antibodies to the N-terminal part of CD163 more than 80% monocytes in human peripheral blood could be identified as CD163 positive, indicating that most, and conceivably all, human peripheral blood monocytes do express CD163.

Serum levels of soluble CD163 in patients with systemic sclerosis

Macrophages may play a role in the pathogenesis of systemic sclerosis (SSc), and CD163-positive M2 macrophages are potentially important source for fibrosis-inducing cytokines. However, no link between M2 macrophages and SSc has been established. The aim is to evaluate the possibility that serum levels of soluble CD163 (sCD163) can be a useful marker for SSc, reflecting M2 activation of macrophages in this disease. Serum sCD163 levels of 43 patients with SSc, 10 patients with scleroderma spectrum disorder (SSD), and 12 healthy controls were measured with specific enzyme-linked immunosorbent assays. SSc patients had significantly higher serum sCD163 levels than healthy controls. The sCD163 levels in SSD patients were higher than healthy controls and lower than SSc patients. Significantly higher right ventricular systolic pressure and lower % DLco levels, and shorter duration of disease were seen in SSc patients with elevated serum sCD163 levels than those with normal levels. These results suggest that sCD163 levels may be increased in proportion to the progression of this disease, indicating the involvement of CD163 in the pathogenesis of SSc. Furthermore, serum sCD163 levels may be a marker of pulmonary hypertension at the early stage in patients with SSc.

Invariant natural killer T cells are natural regulators of murine spondylarthritis

OBJECTIVE

To investigate the role of invariant natural killer T (iNKT) cells in TNF(DeltaARE/+) mice, an animal model of spondylarthritis (SpA) with both gut and joint inflammation.

METHODS

The frequency and activation of iNKT cells were analyzed on mononuclear cells from the lymph nodes and livers of mice, using flow cytometry with alpha-galactosylceramide/CD1d tetramers and quantitative polymerase chain reaction for the invariant V(alpha)14-J(alpha)18 rearrangement. Bone marrow-derived dendritic cells (DCs) were obtained by expansion of primary cells with granulocyte-macrophage colony-stimulating factor followed by coculture with iNKT cell hybridomas, and interleukin-2 release into the cocultures was then measured by enzyme-linked immunosorbent assay (ELISA). Cytokine levels were determined by ELISA or cytometric bead array analyses of freshly isolated DCs and iNKT cells in mixed cocultures. TNF(DeltaARE/+) mice were backcrossed onto J(alpha)18(-/-) and CD1d(-/-) mice, and disease onset was evaluated by clinical scoring, positron emission tomography, and histology. CD1d levels were analyzed on mononuclear cells in paired blood and synovial fluid samples from patients with SpA compared with healthy control subjects.

RESULTS

In the absence of iNKT cells, symptoms of gut and joint inflammation in TNF(DeltaARE/+)mice were aggravated. Invariant NKT cells were activated during the course of the disease. This was linked to an enrichment of inflammatory DCs, characterized by high levels of CD1d, particularly at draining sites of inflammation. A similar increase in CD1d levels was observed on DCs from patients with SpA. Inflammatory DCs from TNF(DeltaARE/+) mice stimulated iNKT cells to produce immunomodulatory cytokines, in the absence of exogenous stimulation. Prolonged, continuous exposure, but not short-term exposure, to tumor necrosis factor (TNF) was found to be responsible for the enhanced DC-NKT cell crosstalk.

CONCLUSION

This mode of iNKT cell activation represents a natural counterregulatory mechanism for the dampening of TNF-driven inflammation.

Circulating soluble interleukin‐2 receptor level predicts remission in very early reactive arthritis

OBJECTIVES

To assess the predictive value of serum soluble interleukin-2 receptor (sIL-2R) levels in patients with acute reactive arthritis (ReA).

METHODS

The study includes 26 patients with acute ReA who had participated in a prospective population-based cohort study of very early arthritis. The patients had had arthritis of at least one joint with a maximum duration of 3 months. They were assessed by a rheumatologist on presentation and 6 months later. Serum sIL-2R levels on presentation were measured by the Immulite automated immunoassay analyser. Remission at 6 months, defined by the absence of swollen and tender joints, was related to the baseline sIL-2R level using a permutation test with general scores. Bootstrap estimation was used to derive the 95% confidence interval (CI).

RESULTS

A total of 17 patients (65%) were in remission at 6 months and nine patients (35%) still had joint symptoms. In patients reaching remission within 6 months, the mean baseline sIL-2R level, 891 U/mL (95% CI: 658 to 1123), was higher than in patients not reaching remission, 501 U/mL (95% CI: 436 to 566), p = 0.022.

CONCLUSIONS

A high serum sIL-2R level at baseline is a predictor of remission in patients with acute ReA.

Diagnostic value of soluble CD163 serum levels in patients suspected of meningitis: Comparison with CRP and procalcitonin

The aim of the study was to evaluate and compare the diagnostic value of sCD163 serum levels with CRP and PCT in meningitis and bacterial infection. An observational cohort study was conducted between February 2001 and February 2005. The study population comprised 55 patients suspected of meningitis on admission to a 27-bed infectious disease department at a Danish university hospital. Biomarker serum levels on admission were measured. Sensitivity and specificity were evaluated at pre-specified cut-off values and overall diagnostic accuracies were compared using receiver-operating characteristic AUCs (areas under curves). Patients were classified by 2 sets of diagnostic criteria into: A) purulent meningitis, serous meningitis or non-meningitis, and B) systemic bacterial infection, local bacterial infection or non-bacterial disease. An elevated serum level of sCD163 was the most specific marker for distinguishing bacterial infection from non-bacterial disease (specificity 0.91; sensitivity 0.47). However, the overall diagnostic accuracy of CRP (AUC =0.91) and PCT (AUC =0.87) were superior (p<0.02 and p<0.06) compared to that of sCD163 (AUC =0.72). For the diagnosis of systemic bacterial infection, the AUC of sCD163 (0.83) did not differ significantly from those of CRP or PCT. All markers had AUCs <0.75 for differentiating between purulent meningitis and other conditions. In conclusion, CRP and PCT had high diagnostic value and were superior as markers of bacterial infection compared to sCD163. However, sCD163 may be helpful in rapid identification of patients with systemic bacterial infection. If used as an adjunct to lumbar puncture, PCT and CRP had very high diagnostic accuracy for distinguishing between bacterial and viral infection in patients with spinal fluid pleocytosis. However, none of the markers was useful as an independent tool for the clinical diagnosis of patients with purulent meningitis.

Progress in spondylarthritis. Immunopathogenesis of spondyloarthritis: which cells drive disease?

Spondyloarthritides, or SpA, form a cluster of chronic inflammatory diseases with the axial skeleton as the most typical disease localisation, although extra-articular manifestations such as intestinal inflammation may frequently occur during the course of the disease. This review summarises recent progress in our understanding of the immunopathogenesis of SpA with special emphasis on the cellular constituents considered to be responsible for the initiation and/or perpetuation of inflammation. There are several arguments favouring a role for haematopoietic cells in the pathophysiology of spondyloarthritis, including HLA-B27-associated dendritic cell disturbances, HLA-B27 misfolding properties and T helper 17 cells. In addition, recent studies have pointed toward a pivotal role for stromal cells. A major challenge, however, remains to determine how recently identified genetic associations such as interleukin-23 receptor polymorphisms may influence cellular targets in spondyloarthritis.

Absence of a classically activated macrophage cytokine signature in peripheral spondylarthritis, including psoriatic arthritis

OBJECTIVE

Peripheral spondylarthritis (SpA) is characterized by macrophages that express CD163, a marker of alternative activation (M2). The purpose of this study was to assess whether this differential infiltration with macrophage subsets was associated with a different local inflammatory milieu in SpA as compared with rheumatoid arthritis (RA).

METHODS

The effect of SpA and RA synovial fluid (SF) on macrophage polarization was tested in vitro on normal peripheral blood monocytes. SF levels of classically activated macrophage (M1)-derived and alternatively activated macrophage (M2)-derived mediators were analyzed by enzyme-linked immunosorbent assay and multiparameter Luminex bead assay in 47 patients with non-psoriatic SpA, 55 with RA, and 15 with psoriatic arthritis (PsA). Paired synovial biopsy samples were analyzed histologically.

RESULTS

SF from SpA patients promoted preferential expression of the M2 markers CD163 and CD200R in vitro, even if SF levels of the prototypical M2-polarizing factors (interleukin-4 [IL-4], IL-13, and IL-10) were not increased as compared with those in RA SF. Despite a similar degree of overall joint inflammation in SpA and RA, SpA synovitis displayed strongly reduced SF levels of M1-derived, but not M2-derived, mediators, such as tumor necrosis factor alpha (TNFalpha), IL-1beta, IL-12p70, and interferon-gamma-inducible protein 10. SF levels of M1-derived mediators correlated well with peripheral joint inflammation in RA, but neither these mediators nor IL-1alpha and IL-17 did so in SpA. Of interest, the SF cytokine profile in PsA, a more destructive subtype of SpA, was similar to that in non-psoriatic SpA.

CONCLUSION

The local inflammatory milieu is clearly different in SpA as compared with RA peripheral arthritis. Synovitis in SpA, including that in PsA, is characterized by a selective decrease in M1-derived proinflammatory mediators, such as TNFalpha and IL-1beta.

Psoriatic disease--from skin to bone

Psoriatic arthritis is an inflammatory joint disease that is heterogeneous in presentation and clinical course. Evidence that this disease is distinct from rheumatoid arthritis and other spondyloarthropathies is based on data derived from characteristic clinical features, histopathologic analyses, immunogenetic associations and musculoskeletal imaging. Emphasis has centered previously on a dominant role for the T lymphocyte in the inflammatory process; however, studies provide support for a major contribution from monocyte-macrophages in the initiation and perpetuation of joint and skin inflammation. The occurrence of arthritis in the absence of psoriasis in a minority of patients with psoriatic arthritis, coupled with divergent genetic risk factors, indicates that psoriatic arthritis is distinct from psoriatic skin inflammation. A new terminology, psoriatic disease, has emerged that encompasses the various manifestations of tissue and organ involvement observed in many psoriasis patients, including inflammation in the joint, eye and gut. Moreover, adverse cardiovascular and metabolic outcomes in patients with psoriasis or psoriatic arthritis might be directly linked to the cutaneous and musculoskeletal manifestations of these diseases via subsets of circulating monocytes and tissue macrophages activated by inflammatory cytokine networks that arise in the skin and possibly the joint.

Differential expression of monocyte CD163 in single- and dual-asthmatic responders during allergen-induced bronchoconstriction

BACKGROUND

Mononuclear phagocytes play an important role in modulating inflammatory reactions in response to antigen challenge.

OBJECTIVE

To investigate the regulation of CD163, a marker of anti-inflammatory macrophages, during Dermatophagoides pteronyssinus (Dp)-induced bronchoconstriction.

METHODS

Among 110 Dp-sensitive patients who underwent bronchial challenge with Dp, there were 51 dual responders (DR), 32 single responders (SR) and 27 non-responders (NR). Monocyte expression of CD14 and CD163 was evaluated by flow cytometry. Exhaled NO (eNO) concentration was determined on-line using a chemiluminescence analyser. In 21 DR, nine SR and 13 NR-soluble CD163 in plasma was measured by ELISA before, 1, 8 and 24 h after the challenge.

RESULTS

In DR, the baseline expression of monocyte CD163 and eNO were significantly greater than in SR and NR. A pattern of (1) decreased monocyte CD163 expression, (2) unchanged sCD163 and (3) increased eNO in DR was contrasted by a pattern of (1) increased CD163 expression, (2) increased sCD163 and (3) unchanged eNO in SR. During allergen challenge, the changes in monocyte CD163 expression and sCD163 inversely correlated with the changes in eNO.

CONCLUSION

Both pro-inflammatory and anti-inflammatory responses to allergen challenge are uniquely expressed among SR and DR.

Proteolytic shedding of the macrophage scavenger receptor CD163 in multiple sclerosis

The scavenger receptor CD163 is selectively expressed on tissue macrophages and human monocytes. CD163 has been implicated to play a role in the clearance of hemoglobin and in the regulation of cytokine production by macrophages. Membrane CD163 can be cleaved by matrix metalloproteinases (MMP) resulting in soluble CD163 (sCD163). In the present report the shedding of CD163 was investigated in multiple sclerosis (MS). An upregulation of plasma sCD163 and a down regulation of membrane CD163 in MS patients compared to healthy controls was observed. The levels of plasma sCD163 correlated with plasma MMP-9 levels in controls, but not in MS patients. Moreover, evidence was obtained for CD163-cleaving MMP activity in plasma of MS patients. Finally, the increased proteolytic shedding of CD163 correlated to reduced plasma levels of circulating inflammatory cytokines. Collectively, our results provide evidence for proteolytic shedding of CD163 in MS and suggest a possible link to cytokine production.

Phenotypic variation in myocardial macrophage populations suggests a role for macrophage activation in SIV-associated cardiac disease

Cardiac abnormalities are common in HIV-infected individuals, and have been especially well documented as contributors to mortality in HIV-infected children. Underlying pathogenetic mechanisms responsible for myocardial disease in HIV-infection remain imperfectly understood. SIV-infected rhesus monkeys develop a spectrum of cardiac lesions similar to those seen in HIV-infected people, providing an important model for pathogenesis studies. Retrospective analysis of cardiac tissue collected at necropsy from SIV-infected rhesus monkeys was performed to evaluate myocardial macrophage and dendritic cell populations as a function of previously quantitated lymphocytic inflammatory infiltrates and cardiomyocyte degeneration or necrosis. Variations in the size and phenotype of macrophage and dendritic cell populations were examined as possible contributors to the pathogenesis of SIV-associated inflammatory lesions. Macrophages labeling immunohistochemically for CD163 differed substantially from macrophages labeling for HAM56 in overall number, distribution across groups, involvement in inflammatory clusters, correlation with the DC-SIGN(+) subpopulation of macrophages, and correlation with numbers of SIV-infected cells. CD163(+) macrophages occurred in significantly higher numbers in uninflamed hearts from SIV-infected animals than in hearts from SIV-infected animals with myocarditis or uninfected controls (p < 0.01). Numbers of CD163(+) cells correlated positively with numbers of SIV-infected cells (p < 0.05) suggesting that the CD163(+) population was associated with decreased inflammatory infiltration and reduced control of virus within the heart. As CD163 has been associated with nonclassical macrophage activation and an antiinflammatory phenotype, these results suggest that a balance between classical and nonclassical activation may affect levels of inflammatory infiltration and of myocardial virus burden.

Ankylosing spondylitis and bowel disease

Between 5 and 10% of cases of ankylosing spondylitis (AS) are associated with inflammatory bowel disease (IBD), either Crohn's disease or ulcerative colitis. A much larger percentage of AS patients have subclinical gut inflammation manifested either by endoscopic findings or by histology. The association with HLA-B27 is less strong in IBD-associated AS than in idiopathic AS, and there is evidence for an association between gut inflammation in AS with the Crohn's-disease-related CARD15 mutations. Despite the different genetics, the immunopathology suggests common inflammatory pathways in gut and joint inflammation in AS, and in gut inflammation in AS and IBD. Although this observation is of interest to unravel the pathophysiology of the disease, systematic screening of AS patients by ileocolonoscopy is not indicated in the absence of gut symptomatology as only a small proportion of AS patients with subclinical gut inflammation will develop overt IBD over time. Treatment of AS associated with IBD with non-steroidal anti-inflammatory drugs (NSAIDs) is problematic because of concerns of potential re-activation of IBD by NSAIDs. Major advances have been made in recent years with the establishment of anti-tumour necrosis factor (TNF) therapy in AS, the other spondyloarthritides and IBD. Anti-TNF agents are of particular relevance to AS patients with concomitant IBD who are at risk of exacerbation of the underlying bowel disease when treated with NSAIDs. In IBD, infliximab, unlike etanercept, is effective in treating clinical symptoms, inducing and maintaining remission, and mucosal healing. Adalimumab appears to be effective in treating both AS and IBD; however, official approval is pending. Currently, infliximab is the drug of choice for the treatment of patients with active AS associated with IBD.

Pathogenesis of ankylosing spondylitis: current concepts

More than three decades after the discovery of HLA-B27 as a major genetic clue to the origins of ankylosing spondylitis, much has been learned about pathogenesis. However, the role of this major histocompatibility complex class I allele remains undefined. Studies from animal models have demonstrated that HLA-B27 overexpression can cause inflammatory disease with spondyloarthritis features, and together with investigations of patient-derived material, both innate adaptive and immune responses have been implicated. The gastrointestinal immune response to pathogens and even normal flora, with subclinical or overt inflammation, may play a role as an environmental component of these diseases. Although there has been a large conceptual emphasis on mechanisms involving autoreactive T-cell recognition of HLA-B27 complexes displaying arthritogenic peptides, and more recently non-canonical recognition of abnormal forms of HLA-B27 free of beta(2)m (heavy-chain dimers or monomers), it remains unclear whether immunological recognition plays a role in pathogenesis. The recognition that the HLA-B27 heavy chain misfolds during assembly, and causes endoplasmic reticulum 'stress', has led to the observation that this activates the unfolded protein response. This has opened additional areas of investigation into the response of immune system cells to protein misfolding, and suggested novel alternative concepts that may explain the role of HLA-B27 in pathogenesis. This chapter will discuss available data and current concepts regarding the pathogenesis of ankylosing spondylitis.

Cutaneous wound healing is impaired in hemophilia B

We used a mouse model to test the hypothesis that the time course and histology of wound healing is altered in hemophilia B. Punch biopsies (3 mm) were placed in the skin of normal mice and mice with hemophilia. The size of the wounds was measured daily until the epidermal defect closed. All wounds closed in mice with hemophilia by 12 days, compared with 10 days in normal animals. Skin from the area of the wound was harvested at different time points and examined histologically. Hemophilic animals developed subcutaneous hematomas; normal animals did not. Macrophage infiltration was significantly delayed in hemophilia B. Unexpectedly, hemophilic mice developed twice as many blood vessels in the healing wounds as controls, and the increased vascularity persisted for at least 2 weeks. The deposition and persistence of ferric iron was also greater in hemophilic mice. We hypothesize that iron plays a role in promoting excess angiogenesis after wounding as it had been proposed to do in hemophilic arthropathy. We have demonstrated that impaired coagulation leads to delayed wound healing with abnormal histology. Our findings have significant implications for treatment of patients with hemophilia, and also highlight the importance of rapidly establishing hemostasis following trauma or surgery.

Serum levels of soluble CD163 correlate with the inflammatory process in coeliac disease

BACKGROUND

In coeliac disease, following the introduction of a gluten-free diet, monitoring mucosal disease activity requires repeated small intestinal biopsies. If a test measuring a circulating inflammatory marker was available, this would be clinically valuable.

AIM

To determine if levels of soluble CD163, a scavenger receptor shed by tissue macrophages, correlated with the inflammatory lesion in coeliac disease.

METHODS

Serum samples were collected from 131 patients with untreated coeliac disease, 40 patients with treated coeliac disease, 92 non-coeliac disease control subjects and 131 healthy controls. A capture enzyme linked immunosorbance assay was established to measure levels of soluble CD163 in sera. The extent of the histological lesion in coeliac biopsies was assessed using a Marsh grading system.

RESULTS

Levels of CD163 in untreated coeliac subjects were significantly elevated when compared with the treated coeliac patients, the disease control group and the healthy control subjects (P < 0.0001 in each instance). Moreover, coeliac patients with the most marked histological lesion (Marsh 3) had significantly higher levels of soluble CD163 than patients with Marsh grade 2 lesions (P < 0.0004), with grade 1 lesions (P < 0.0001) and grade 0 lesions (P < 0.0001).

CONCLUSIONS

Measurement of soluble CD163 may be a useful method of monitoring the inflammatory lesion in coeliac disease.

Identification of synovial biomarkers of response to experimental treatment in early-phase clinical trials in spondylarthritis

OBJECTIVE

To identify biomarkers for effective treatment in early-phase clinical trials of spondylarthritis (SpA), by analyzing which synovial features can be reliably identified in patients with SpA.

METHODS

Synovial biopsies were performed at weeks 0 and 12 in 20 SpA patients treated with infliximab, 20 treated with etanercept, and 12 who were not treated. Primary clinical outcome measures were patient and physician global assessment of disease activity. Extensive histologic evaluation included assessment of lining layer hyperplasia, vascularity, markers of cellular infiltration, and metalloproteinases (MMPs) in the lining and sublining layers.

RESULTS

Changes in levels of CD163 (resident tissue macrophages) in the lining, and CD163, MMP-3, and myeloid-related protein 14 (MRP-14; infiltrating myeloid cells) in the sublining correlated significantly with changes in the primary clinical outcomes. Comparison between responders (n = 35) and nonresponders (n = 17) showed differences in the degree of change in the levels of CD163 in the lining and CD163, MMP-3, and CD3 in the sublining, whereas trends in change in the levels of MRP-8 and MRP-14 in the lining and sublining were similar in the 2 groups. Accordingly, the highest differences in standardized response means (SRMs) between the 2 groups were found for CD163 in the lining, MMP-3, CD163, CD3, and MRP-8 in the sublining, and the level of polymorphonuclear cells (PMNs). When comparing treated and untreated patients, high differences in SRMs were again found for CD163 in the lining, MMP-3, CD163, and MRP-8 in the sublining, and PMNs. These parameters performed prognostically as well as the erythrocyte sedimentation rate and better than the C-reactive protein level. Class prediction analysis yielded a 90% correct prediction using 8 synovial parameters, as follows: lining and sublining CD163, MRP-8, and MRP-14, sublining MMP-3, and PMNs. In validation analyses with independent samples, effective treatment was correctly predicted in 24 of 30 SpA patients and in 2 of 2 placebo-treated patients.

CONCLUSION

Changes in synovial macrophage subsets, PMN levels, and MMP-3 expression reflect response to treatment in SpA. The ability of these parameters to correctly identify effective therapy makes them interesting biomarkers for use in early-phase clinical trials in SpA.

Biomarkers in spondyloarthritis

In spondyloarthritis, in particular ankylosing spondylitis (AS), a need exists for clinically meaningful biomarkers, both for diagnosis and prognosis. Earlier diagnosis has become an imperative since the advent of biologic therapy, which has proved effective in controlling axial inflammation. Presently, however, there are no biomarkers that reliably distinguish inflammatory back pain from the far more prevalent mechanical back pain. The target sites in AS--sacroiliac joints and the spine--are relatively inaccessible to the investigator and clinician, so defining markers associated with or predictive of axial inflammation remains an important goal. Cytokines, metalloproteinases, and cartilage catabolic products are all candidates for the important role of biomarker in spondyloarthritis.

Pathogenesis of spondyloarthritis: Insights from synovial membrane studies

Here, we review histopathologic studies of the cellular and molecular pathways of spondyloarthritis (SpA) synovial inflammation. In contrast with lymphocytes, specific macrophage subsets and polymorphonuclear cells selectively increase in SpA synovitis, correlate with global disease activity, decrease rapidly upon effective treatment with tumor necrosis factor (TNF)-alpha blockers, and serve as valuable biomarkers for treatment response in SpA. Functionally, increased Toll-like receptor triggering may be responsible for the proinflammatory response of these cells. Therefore, we propose that an exaggerated response of the innate immune system in genetically susceptible patients rather than a classic, lymphocyte-mediated autoimmune process is involved in the pathogenesis of SpA.

Synovial inflammation does not change in the absence of effective treatment: implications for the use of synovial histopathology as biomarker in early phase clinical trials in rheumatoid arthritis

OBJECTIVES

To determine the impact on synovial histopathology of changes in clinical disease activity in the absence of effective treatment.

METHODS

Twelve patients with active RA not receiving effective treatment were studied over a 14 week period. Synovial biopsy specimens obtained at baseline and week 14 were analysed by histology and immunohistochemistry.

RESULTS

Over the course of 14 weeks, there was a trend towards a decrease of the DAS28, with 7/12 patients being good or moderate DAS28 responders despite the absence of effective treatment. Patients' assessment of global disease activity and swollen joint count both decreased significantly. Histologically, there was a decrease of lining layer hyperplasia and lymphoid aggregates, a similar trend for vascularity, but there was no effect on global synovial infiltration. Accordingly, there was no decrease of the cellular infiltration with T lymphocytes (CD3, CD4, CD8), B lymphocytes (CD20), plasma cells (CD38), dendritic cells (CD1a, CD83), and even an increase of CD163+ sublining macrophages, with a similar trend for CD68+ sublining macrophages. The changes in DAS28 scores in these patients did not correlate with changes in histological variables, with the exception of an inverse correlation with plasma cells. Remarkably, even in the DAS28 responders, no significant changes in synovial inflammatory infiltration were noted.

CONCLUSIONS

Despite variations in global disease activity, synovial inflammatory infiltration did not change significantly in the absence of effective treatment. The lack of a placebo effect on synovial markers of treatment response such as sublining macrophages can facilitate conclusive early phase trials with small numbers of patients with RA.

Immunomodulatory effects of etanercept on peripheral joint synovitis in the spondylarthropathies

OBJECTIVE

Because different tumor necrosis factor alpha (TNFalpha) blockers may have distinct immunomodulatory effects on specific disease manifestations, the present study was carried out to investigate the immunomodulating effects of etanercept on peripheral synovitis in the spondylarthropathies (SpA).

METHODS

Peripheral joint disease was assessed clinically, histologically, and radiologically in a prospective 2-year study of 20 patients with SpA treated with etanercept. Synovial tissue biopsy samples obtained at weeks 0, 12, and 52 were analyzed by histology and immunohistochemistry for the extent of inflammation, changes to tissue architecture, and matrix degradation. Serum levels of myeloid-related protein 8 (MRP-8)/MRP-14, matrix metalloproteinase 3 (MMP-3), and cartilage oligomeric matrix protein (COMP) were determined by enzyme-linked immunosorbent assay.

RESULTS

Etanercept induced a rapid and sustained clinical improvement of peripheral joint disease. Histologic synovitis was down-regulated, with a profound reduction in global cellular infiltration and T lymphocytes, but not B lymphocytes. The most prominent change in markers of inflammation was a reduction in the different macrophage subsets (CD68, CD163, MRP-8, and MRP-14), but this was not paralleled by a decrease in serum MRP-8/MRP-14. Structural changes included normalization of lining layer hyperplasia and a moderate reduction in vascularity. However, no effect on the microarchitecture of lymphoid aggregates was observed. In terms of an effect on matrix degradation, the synovial expression of MMP-3 and MMP-9 was down-modulated in correlation with a rapid and profound decrease in serum MMP-3. At week 52, serum COMP levels were also reduced. No significant radiologic disease progression was observed in these patients over a 2-year period.

CONCLUSION

Use of etanercept effectively down-modulated the immunopathologic processes of SpA synovitis, both in the short term and in the long term.

Distinct synovial immunopathologic characteristics of juvenile-onset spondylarthritis and other forms of juvenile idiopathic arthritis

OBJECTIVE

To characterize the synovial immunopathologic features of juvenile-onset spondylarthritis (SpA) in relation to adult SpA and other forms of juvenile idiopathic arthritis (JIA).

METHODS

Synovial biopsy samples were obtained from 10 patients with juvenile-onset SpA, 23 with adult SpA, 19 with rheumatoid arthritis (RA), 8 with juvenile polyarthritis, and 12 with juvenile oligoarthritis. Synovial immunopathologic features were studied by extensive histologic and immunohistochemical analyses.

RESULTS

Synovitis in juvenile SpA was characterized by marked lining layer hyperplasia, clear hypervascularity, and pronounced inflammatory cell infiltration with lymphocytes and macrophages, independent of disease duration or time of sampling. The immunopathologic features of juvenile SpA resembled those of adult SpA in terms of hypervascularity and absence of RA-specific intracellular citrullinated proteins and HLA-DR4/human cartilage glycoprotein 39(263-275) complexes, but differed markedly by a stronger lining layer hyperplasia and lower numbers of CD163+ macrophages. Accordingly, class prediction analysis failed to classify juvenile SpA synovitis in the SpA group. Comparison of juvenile SpA with other JIA subtypes showed a broad overlap, with the exception of slightly lower vascularity in juvenile polyarthritis and higher inflammatory cell infiltration in juvenile oligoarthritis. Unsupervised clustering analysis identified a subgroup of samples characterized by high plasma cell infiltration, which corresponded with active, longstanding JIA, mostly of the oligoarthritis subtype.

CONCLUSION

Despite some similarities with adult SpA, the findings with regard to lining layer hyperplasia and CD163+ macrophage infiltration are indicative of important differences in the synovial immunopathologic features of juvenile-onset SpA. The partial overlap with other JIA subtypes emphasizes the need for further biologic characterization of JIA in order to define pathophysiologic, rather than phenotypic, subgroups.

The macrophage scavenger receptor CD163

Mature tissue macrophages form a first line of defense to recognize and eliminate potential pathogens; these specialized cells are capable of phagocytosis, degradation of self and foreign materials, establishment of cell-cell interactions, and the production of inflammatory mediators. Mature tissue macrophages express a variety of receptors, including the scavenger receptor cystein-rich (SRCR) superfamily members. CD163 is a member of the SRCR family class B and is expressed on most subpopulations of mature tissue macrophages. The best characterized function of CD163, which is essentially a homeostatic one, is related to the binding of Hemoglobin:Haptoglobin complexes. Furthermore, it has been suggested that CD163 positive macrophages or the soluble form of CD163 plays a role in the resolution of inflammation, as they are found in high numbers in inflamed tissue.

Predictive value of soluble haemoglobin scavenger receptor CD163 serum levels for survival in verified tuberculosis patients

Pre-treatment serum levels of sCD163 were measured in a cohort of 236 suspected tuberculosis (TB) cases from Guinea-Bissau, with a median follow-up period of 3.3 years (range 0-6.4 years). In 113 cases, the diagnosis of TB was verified by positive sputum microscopy and/or culture. Among the verified TB cases, a decreased survival rate was found in 27 patients with sCD163 levels above the upper reference limit (3.95 microg/mL). The difference in survival was significant during TB treatment (log rank, p<0.02) and after long-term follow-up (log rank, p<0.001). The decrease in survival rate during TB treatment remained significant in a multivariate Cox model controlling for human immunodeficiency virus (HIV) status, age and gender, with a mortality increase of 1.19 (95% CI, 1.04-1.36) per microg of sCD163, and a hazard ratio (HR) for sCD163 levels above the upper reference limit of 4.18 (95% CI, 1.06-16.4). The difference was not significant after excluding patients with concomitant HIV-1 and HIV-2 infection in Kaplan-Meier analyses (log rank, p 0.11). In contrast, the difference in survival remained significant in Kaplan-Meier analyses after long-term follow-up, even after excluding patients with concomitant HIV-1 and HIV-2 infection (log rank, p 0.002). In the Cox model, the mortality increase per microg of sCD163 was 1.27 (95% CI, 1.14-1.40), with an HR for elevated sCD163 levels of 2.85 (95% CI, 1.44-5.63). The HRs for concomitant HIV-1 and HIV-2 infection were 6.92 (95% CI, 3.28-14.58) and 2.48 (95% CI, 1.09-5.67), respectively. Thus, sCD163 levels appeared to be an independent predictor of survival in verified TB patients.

Pathogenesis of ankylosing spondylitis and reactive arthritis

PURPOSE OF REVIEW

The hallmark of ankylosing spondylitis is acute and chronic spinal inflammation initiating in the sacroiliac joints, often coupled with enthesitis, presenting as chronic inflammation at the sites of ligamentous and tendinous insertions into bone. Peripheral joint synovitis can be a prominent feature as well. Reactive arthritis is a sterile synovitis arising after an extra-articular infection of enteric or urogenital tracts. HLA-B27 has been known for about the past 30 years to be associated with ankylosing spondylitis and reactive arthritis, but the pathogenesis of ankylosing spondylitis and reactive arthritis is still not well defined. Although the clinical manifestations of ankylosing spondylitis and reactive arthritis may differ, this update discusses the two diseases together and focuses on recent evidence in both.

RECENT FINDINGS

With respect to HLA-B27 several recent studies address arthritogenic peptides, molecular mimicry, and aberrant forms of B27. Several candidate genes in addition to B27 have been implicated in recent genetic studies. With respect to bacterial infection, recent findings in bacterial antigenicity, host response through interactions of antigen-presenting cells, T cells, and cytokines are providing new understanding of host-pathogen interactions and the pathogenesis of arthritis. Endogenous host factors such as proteoglycans may play a role as autoantigens and contribute to chronic inflammation on that basis.

SUMMARY

Recent advances provide additional new insights into distinct pathogenetic mechanisms in AS and ReA that arise from a complex interplay between genetic factors including HLA-B27 and environmental factors.

Gut inflammation in the spondyloarthropathies

In this paper, the ample experimental, clinical, genetic, histopathologic, and immunologic evidence for an important role of the gut in the pathogenesis of spondylarthropathy (SpA) and for an overlap between SpA and Crohn's disease is reviewed. These data suggest that SpA and Crohn's disease should be scientifically and clinically considered as distinct phenotypes of common immune-mediated inflammatory disease pathways rather than as separate disease entities. Classification, diagnosis, and therapy based on pathophysiologic insights is likely to become superior to an approach based exclusively on signs and symptoms, as evidenced by the recent evolution in treatment of SpA by tumor necrosis factor-a blockade.

Structure-modifying capacity of anti-tumour necrosis factor-alpha therapy in ankylosing spondylitis

Spondylarthropathies (SpA) present mainly with spondylitis, pauciarticular peripheral arthritis and enthesopathy. Ankylosing spondylitis (AS) is the prototype disease in this concept. Other entities include reactive arthritis, arthritis in patients with inflammatory bowel disease, some forms of psoriatic arthritis and undifferentiated SpA. NSAIDs are the classical cornerstone of medical therapy in patients with SpA. The effect of these drugs on disease progression, more specifically the ankylosis, is uncertain. Sulfasalazine can be combined with NSAIDs, particularly if peripheral arthritis symptoms persist. However, this combination therapy is not effective for the spondylitis symptoms. Indeed, AS is one of the rheumatic diseases for which no real disease-modifying antirheumatic treatment is available. Challenges in chronic autoimmune arthritis have changed dramatically, especially since biotechnological compounds became available. These compounds allow for a specific intervention in the immune cascade underlying the disease. Tumour necrosis factor (TNF)-alpha antagonists (monoclonal antibodies such as infliximab, or soluble receptors such as etanercept) are the first representative drugs in this category. Open-label studies have shown the efficacy of these new targeted drugs, which has been confirmed by controlled studies, at least in the short term. Improvements in several clinical parameters, function, quality of life, biological parameters, histopathological synovial characteristics and magnetic resonance imaging, have all been observed. As a result of these favourable results, anti-TNFalpha therapy has been approved for the treatment of AS and should be considered for patients with severe axial symptoms and elevated serological markers of inflammatory activity who have responded inadequately to conventional nonsteroidal therapy. There is evidence that this new therapeutic approach has a disease- and even structure-modifying effect in SpA. In this context, structure modification should not only be seen as inhibition of bone and cartilage destruction but more broadly as modulation of tissue histology. Some questions remain unanswered, such as the long-term efficacy and safety of anti-TNFalpha therapy, the extent of structural benefit and the cost effectiveness. However, despite these concerns, anti-TNFalpha therapy represents a major therapeutic advancement in the treatment of AS.

Synovial histopathology of psoriatic arthritis, both oligo- and polyarticular, resembles spondyloarthropathy more than it does rheumatoid arthritis

At present only few biological data are available to indicate whether psoriatic arthritis (PsA) is part of the spondyloarthropathy (SpA) concept, whether it is a separate disease entity or a heterogeneous disease group with oligoarticular/axial forms belonging to SpA and polyarticular forms resembling rheumatoid arthritis (RA). To address this issue with regard to peripheral synovitis, we compared the synovial characteristics of PsA with those of ankylosing spondylitis (AS)/undifferentiated SpA (USpA) and RA, and compared the synovium of oligoarticular versus polyarticular PsA. Synovial biopsies were obtained from patients with RA, nonpsoriatic SpA (AS + USpA), and oligoarticular and polyarticular PsA. The histological analysis included examination(s) of the lining layer thickness, vascularity, cellular infiltration, lymphoid aggregates, plasma cells and neutrophils. Also, we performed immunohistochemical assessments of CD3, CD4, CD8, CD20, CD38, CD138, CD68, CD163, CD83, CD1a, CD146, alphaVbeta3, E-selectin, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, S100A12, intracellular citrullinated proteins and major histocompatibility complex (MHC)-human cartilage (HC) gp39 peptide complexes. Comparing SpA (PsA + AS + USpA) with RA, vascularity, and neutrophil and CD163+ macrophage counts were greater in SpA (P < 0.05), whereas lining layer thickness and the number of CD83+ dendritic cells were greater in RA (P < 0.05). In RA, 44% of samples exhibited positive staining for intracellular citrullinated proteins and 46% for MHC-HC gp39 peptide complexes, whereas no staining for these markers was observed in SpA samples. We excluded influences of disease-modifying antirheumatic drug and/or corticosteroid treatment by conducting systematic analyses of treated and untreated subgroups. Focusing on PsA, no significant differences were observed between PsA and nonpsoriatic SpA. In contrast, vascularity (P < 0.001) and neutrophils were increased in PsA as compared with RA (P = 0.010), whereas staining for intracellular citrullinated proteins and MHC-HC gp39 peptide complexes was exclusively observed in RA (both P = 0.001), indicating that the same discriminating features are found in PsA and other SpA subtypes compared with RA. Exploring synovial histopathology between oligoarticular and polyarticular PsA, no significant differences were noted. Moreover, intracellular citrullinated proteins and MHC-HC gp39 peptide complexes, which are specific markers for RA, were observed in neither oligoarticular nor polyarticular PsA. Taken together, these data indicate that the synovial histopathology of PsA, either oligoarticular or polyarticular, resembles that of other SpA subtypes, whereas both groups can be differentiated from RA on the basis of these same synovial features, suggesting that peripheral synovitis in PsA belongs to the SpA concept.

Infiltration of the synovial membrane with macrophage subsets and polymorphonuclear cells reflects global disease activity in spondyloarthropathy

Considering the relation between synovial inflammation and global disease activity in rheumatoid arthritis (RA) and the distinct but heterogeneous histology of spondyloarthropathy (SpA) synovitis, the present study analyzed whether histopathological features of synovium reflect specific phenotypes and/or global disease activity in SpA. Synovial biopsies obtained from 99 SpA and 86 RA patients with active knee synovitis were analyzed for 15 histological and immunohistochemical markers. Correlations with swollen joint count, serum C-reactive protein concentrations, and erythrocyte sedimentation rate were analyzed using classical and multiparameter statistics. SpA synovitis was characterized by higher vascularity and infiltration with CD163⁺ macrophages and polymorphonuclear leukocytes (PMNs) and by lower values for lining-layer hyperplasia, lymphoid aggregates, CD1a⁺ cells, intracellular citrullinated proteins, and MHC–HC gp39 complexes than RA synovitis. Unsupervised clustering of the SpA samples based on synovial features identified two separate clusters that both contained different SpA subtypes but were significantly differentiated by concentration of C-reactive protein and erythrocyte sedimentation rate. Global disease activity in SpA correlated significantly with lining-layer hyperplasia as well as with inflammatory infiltration with macrophages, especially the CD163⁺ subset, and with PMNs. Accordingly, supervised clustering using these synovial parameters identified a cluster of 20 SpA patients with significantly higher disease activity, and this finding was confirmed in an independent SpA cohort. However, multiparameter models based on synovial histopathology were relatively poor predictors of disease activity in individual patients. In conclusion, these data indicate that inflammatory infiltration of the synovium with CD163⁺ macrophages and PMNs as well as lining-layer hyperplasia reflect global disease activity in SpA, independently of the SpA subtype. These data support a prominent role for innate immune cells in SpA synovitis and warrant further evaluation of synovial histopathology as a surrogate marker in early-phase therapeutic trials in SpA.

Differential expression and response to anti-TNFα treatment of infiltrating versus resident tissue macrophage subsets in autoimmune arthritis

Synovial macrophages play a pivotal role in the pathogenesis of chronic autoimmune arthritis by contributing to local inflammation and tissue damage and are therefore a primary target for therapeutic intervention. The aim of the present study was to investigate in more detail the relative contribution of different synovial macrophage subsets with potentially different inflammatory or anti-inflammatory functions by analysing the two most frequent forms of human autoimmune arthritis, spondyloarthropathy (SpA) and rheumatoid arthritis (RA). Both infiltrating macrophages from peripheral blood expressing myeloid-related proteins (MRP) 8 and 14, and resident tissue macrophages expressing CD163 were abundant in inflamed synovium. Whereas the global number of synovial macrophages was similar in both diseases, infiltrating macrophages were increased in the RA lining layer in contrast with resident tissue macrophages, which were more frequently observed in SpA. Soluble MRP8/MRP14 complexes, which were secreted locally in the joint during the infiltration process, were increased in the serum of arthritis patients and, in contrast with soluble CD163 shed from resident tissue macrophages, correlated well with global inflammatory parameters. Treatment in vivo with anti-TNFalpha had a rapid and pronounced effect on the infiltration of MRP-positive macrophages into tissues, as evidenced by histopathological analysis and serum MRP8/MRP14 levels. Taken together, these data support an important role for infiltrating versus resident tissue macrophages in human autoimmune synovitis and indicate that macrophage products such as soluble MRP8/MRP14 complexes are valuable biomarkers for the experimental and clinical monitoring of specific disease mechanisms in vivo.

Tumor necrosis factor α blockade treatment down-modulates the increased systemic and local expression of toll-like receptor 2 and toll-like receptor 4 in spondylarthropathy

OBJECTIVE

Abnormal host defense against pathogens has been implicated in the pathogenesis of spondylarthropathy (SpA), a disease characterized by abundant synovial infiltration with innate immune cells. Given the role of Toll-like receptors (TLRs) in activation of innate inflammation and the occurrence of TLR-dependent infections after tumor necrosis factor alpha (TNFalpha) blockade treatment, the present study was undertaken to analyze TLRs and their modulation by TNFalpha blockade in SpA.

METHODS

Peripheral blood mononuclear cells (PBMCs) were obtained from SpA and rheumatoid arthritis (RA) patients during infliximab therapy, and from healthy controls. TLR-2 and TLR-4 expression and TNFalpha production upon lipopolysaccharide (LPS) stimulation were analyzed by flow cytometry on different monocyte subsets. Synovial biopsy specimens from 23 SpA patients before and after infliximab or etanercept treatment, from 15 RA patients, and from 18 osteoarthritis (OA) patients were analyzed by immunohistochemistry.

RESULTS

Expression of TLR-4, but not TLR-2, was increased on PBMCs from patients with SpA, whereas both TLRs were increased in RA patients. TLR expression was particularly increased on the CD163+ macrophage subset. Infliximab reduced TLR-2 and TLR-4 expression on monocytes of SpA and RA patients, leading to lower levels than in controls and to impaired TNFalpha production upon LPS stimulation. In inflamed synovium, the expression of both TLRs and of CD163 was significantly higher in patients with SpA than in those with RA or OA. Paralleling the systemic effect, TLRs in synovium were down-regulated following treatment with infliximab as well as etanercept, indicating a class effect of TNFalpha blockers.

CONCLUSION

Inflammation in SpA is characterized by increased TLR-2 and TLR-4 expression, which is sharply reduced by TNFalpha blockade. These findings suggest a potential role of innate immunity-mediated inflammation in SpA and provide an additional clue regarding the mechanism of action as well as the potential side effects of TNFalpha blockade.

Histological evidence that infliximab treatment leads to downregulation of inflammation and tissue remodelling of the synovial membrane in spondyloarthropathy

OBJECTIVE

To confirm and extend the immunopathological evidence of effects of infliximab on the synovium in active spondyloarthropathy.

METHODS

Synovial biopsies obtained in patients with spondyloarthropathy at baseline and week 12 were stained and scored by two independent observers. Two study populations were evaluated: I, a cohort of 10 patients treated with 5 mg/kg infliximab at week 0, 2, and 6, plus three placebo treated patients; and II, a pooled cohort of 20 patients fulfilling identical inclusion and exclusion criteria and treated with the same loading dose regimen.

RESULTS

In study population I, treatment with infliximab induced reduction in synovial lining layer thickness (p = 0.015), endothelial activation (E-selectin, p = 0.034), and inflammatory cell infiltration with neutrophils (p = 0.041), macrophages (p = 0.034), and T cells (p = 0.026), but not with B cells and plasma cells; no such trends were observed in the placebo treated patients. Besides confirming the highly significant downregulation of inflammation, analysis of cohort II showed structural changes such as normalisation of lining layer thickness (p = 0.030), reduction in the number of blood vessels (p = 0.039), and downregulation of follicular organisation (p = 0.050). No differences in histopathological response were observed between spondyloarthropathy subtypes.

CONCLUSIONS

Profound immunomodulatory changes in the synovium parallel the clinical benefit in patients with spondyloarthropathy treated with infliximab, independently of the subtype. The study provides histological evidence that TNF alpha blockade not only downregulates inflammation but also leads to tissue remodelling.