Biomarkers have been actively investigated to supplement functional and imaging modalities to predict the severity, therapeutic responsiveness, and progression of connective tissue disease-associated interstitial lung disease (CTD-ILD). This study aimed to evaluate Krebs von den Lungen 6 (KL-6) as a potential biomarker reflecting the severity of CTD-ILD as assessed through computed tomography (CT) and pulmonary function test (PFT) parameters. This retrospective study included 549 Korean patients with rheumatoid arthritis, systemic sclerosis, inflammatory myositis, and other CTDs with or without concurrent ILD. Serum KL-6 concentration (U/mL) was measured using the latex-enhanced immunoturbidimetric assay method. CT and PFT results were collected within 1 year of serum collection. A semiquantitative grade of ILD extent was evaluated through CT scan (grade 1, 0–25%; grade 2, 26–50%; grade 3, 51–75%; grade 4, 76–100%). CTD-ILD patients (n = 165) had elevated serum KL-6 levels compared to CTD patients without ILD (n = 384) (p < 0.001), and those findings were preserved after adjusting for age, sex, and CTD type. The semiquantitative grade of ILD on CT scan was significantly proportional to the KL-6 level, and the optimal cut-off KL-6 value effectively differentiated each ILD grade. The percent diffusing capacity of the lung for carbon monoxide (DLCO) (p < 0.001) and forced vital capacity (FVC) (p < 0.001) parameters had a moderate, negative correlation with the KL-6 level. Serum KL-6 levels were increased in CTD-ILD patients and had a positive correlation with CT grade and a negative correlation with FVC and DLCO. Serum KL-6 levels may reflect CTD-ILD severity.

Rheumatoid arthritis (RA) is a systemic inflammatory autoimmune disease, characterized by chronic, erosive polyarthritis and by the presence of various autoantibodies in serum and synovial fluid. Since rheumatoid factor (RF) was first described, a number of other autoantibodies have been discovered in RA patients. The autoantigens recognized by these autoantibodies include cartilage components, chaperones, enzymes, nuclear proteins and citrullinated proteins. However, the clinical significances and pathogenic roles of these antibodies are largely unknown except for RF and anticitrullinated protein antibodies (ACPAs), whose clinical usefulness has been acknowledged due to their acceptable sensitivities and specificities, and prognostic values. This review presents and discusses the current state of the art regarding RF and ACPA in RA.

Objective: Interferon‐γ–inducible protein 10 (IP‐10; also called CXCL10), a chemokine important in the migration and proliferation of T cells, is induced in a wide variety of cell types. However, the role of IP‐10 in rheumatoid arthritis (RA) remains largely unknown. The purpose of this study was to examine the potential role of IP‐10 in bone resorption and RA through examination of a mouse model of collagen‐induced arthritis (CIA).Methods: The effects of IP‐10 on mouse T cells during osteoclast differentiation were examined in migration assays. The bone‐erosive activity of IP‐10 was determined in vivo in a mouse model of CIA by histologic and immunostaining analyses. Cytokine levels in serum and culture medium were measured with sandwich enzyme‐linked immunosorbent assays.Results: Serum concentrations of IP‐10 were significantly higher in mice with CIA than in control mice. RANKL greatly induced IP‐10 expression in osteoclast precursors, but not in mature osteoclasts. IP‐10 stimulated the expression of RANKL and tumor necrosis factor α (TNFα) in CD4+ T cells and induced osteoclastogenesis in cocultures of CD4+ T cells and osteoclast precursors. However, IP‐10 did not induce RANKL or TNFα in CD8+ T cells. Treatment with neutralizing antibody to IP‐10 significantly inhibited the infiltration of CD4+ T cells and F4/80+ macrophages into the synovium and attenuated bone destruction in mice with CIA. Furthermore, levels of RANKL and TNFα were inhibited by antibody to IP‐10. Bone erosion was observed in mice infected with an IP‐10 retrovirus.Conclusion: Our findings suggest that IP‐10 plays a critical role in the infiltration of CD4+ T cells and F4/80+ macrophages into inflamed joints and causes bone destruction. Our results provide the first evidence that IP‐10 contributes to the recruitment of inflammatory cells and is involved in bone erosion in inflamed joints.

Introduction: Adiponectin has been implicated in the pathogenesis of osteoarthritis (OA). We studied the effects of adiponectin on the OA cartilage homeostasis. Methods: Immunohistochemical analysis was performed to evaluate differential expression of adiponectin receptors (AdipoRs) in nonlesional and lesional areas of OA cartilage. Cartilage and chondrocytes from the knee joints of primary OA patients were cultured in the presence of adiponectin (0~30 μg/ml). The levels of total nitric oxide (NO), matrix metalloproteinase (MMP)-1, -3, and -13, and tissue inhibitor of metalloproteinase (TIMP)-1 were measured in the conditioned media. The levels of inducible NO synthase (iNOS) and MMPs were determined with the quantitative real-time reverse transcription-polymerase chain reaction. The concentrations of collagenase-cleaved type II collagen neoepitope (C1-2C) were determined in the supernatant of adiponectin-stimulated OA cartilage explants. The effects of kinase and NOS inhibitors were evaluated in the adiponectin-stimulated chondrocytes. Results: The expression levels of both AdipoR1 and AdipoR2 were significantly higher in lesional than in nonlesional areas of OA cartilage. The increased rate of AdipoR1-positive chondrocytes was twice that of AdipoR2-positive chondrocytes when compared between nonlesional and lesional areas. Adiponectin-stimulated OA chondrocytes showed increased total NO and MMP-1, -3, and -13 levels compared with nonstimulated cells. The TIMP-1 level was not affected. The C1-2C levels were increased by adiponectin in OA cartilage explant culture. AMP-activated protein kinase (AMPK) and c-Jun N-terminal kinase (JNK) inhibitors (compound C and SP600125) significantly suppressed adiponectin-induced production of total NO and MMP-1, -3, and -13. Inducible NOS inhibitors enhanced the expression of the adiponectin-induced MMPs. Conclusions: Adiponectin causes matrix degradation in OA cartilage and increases MMPs and iNOS expression via the AMPK and JNK pathways in human OA chondrocytes. The catabolic effects of adiponectin may be counteracted by NO.

Exosomes are involved in intercellular communication. The aim of this study was to investigate whether circulating exosomes effectively contribute to the inflammatory response in systemic lupus erythematosus (SLE). Exosomes were purified from SLE patients and healthy controls (HCs). Healthy peripheral blood mononuclear cells (PBMCs) were stimulated with exosomes isolated from SLE patients and HCs in the presence or absence of Toll-like receptor (TLR) inhibitors. Production of interferon (IFN)-α, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 were measured. Correlation between exosome levels and SLE disease activity was examined. The serum exosomes levels were significantly higher in SLE patients than in HCs. SLE exosomes induced a higher production of IFN-α, TNF-α, IL-1β, and IL-6 compared to healthy exosomes. SLE serum that was depleted of exosomes and SLE exosomes that were mechanically disrupted failed to induce any significant cytokine production. Exosome-mediated production of TNF-α, IL-1β, and IL-6 was decreased by the TLR4 antagonist, whereas that of IFN-α was suppressed by the TLR1/2, TLR7, and TLR9 antagonists. Exosome levels correlated with disease activity in SLE patients (rho = 0.846, p = 0.008). The circulating exosomes are immunologically active and their levels correlate with disease activity in SLE patients. The circulating exosomes might serve as novel biomarkers of SLE disease activity.