Complement component C1q is produced by isolated articular chondrocytes.

OBJECTIVE: Inflammation and innate immune responses may contribute to development and progression of Osteoarthritis (OA). Chondrocytes are the sole cell type of the articular cartilage and produce extracellular-matrix molecules. How inflammatory mediators reach chondrocytes is incompletely understood. Previous studies have shown that chondrocytes express mRNA encoding complement proteins such as C1q, suggesting local protein production, which has not been demonstrated conclusively. The aim of this study is to explore C1q production at the protein level by chondrocytes. DESIGN: We analysed protein expression of C1q in freshly isolated and cultured human articular chondrocytes using Western blot, ELISA and flow cytometry. We examined changes in mRNA expression of collagen, MMP-1 and various complement genes upon stimulation with pro-inflammatory cytokines or C1q. mRNA expression of C1 genes was determined in articular mouse chondrocytes. RESULTS: Primary human articular chondrocytes express genes encoding C1q, C1QA, C1QB, C1QC, and secrete C1q to the extracellular medium. Stimulation of chondrocytes with pro-inflammatory cytokines upregulated C1QA, C1QB, C1QC mRNA expression, although this was not confirmed at the protein level. Extracellular C1q bound to the chondrocyte surface dose dependently. In a pilot study, binding of C1q to chondrocytes resulted in changes in the expression of collagens with a decrease in collagen type 2 and an increase in type 10. Mouse articular chondrocytes also expressed C1QA, C1QB, C1QC, C1R and C1S at the mRNA level. CONCLUSIONS: C1q protein can be expressed and secreted by human articular chondrocytes and is able to bind to chondrocytes influencing the relative collagen expression.

Complement levels and anti-C1q autoantibodies in patients with neuropsychiatric systemic lupus erythematosus.

OBJECTIVE: The objective of this paper is to analyse serum levels of anti-C1q, C1q circulating immune complexes (CIC), complement activation and complement components in systemic lupus erythematosus (SLE) patients during the first central nervous system neuropsychiatric (NP) event and to define the possible association between these results and clinical and laboratory characteristics. METHODS: A total of 280 patients suspected of having NP involvement due to SLE were recruited in the Leiden NPSLE-clinic. All SLE patients were classified according to the ACR 1982 revised criteria for the classification of SLE. The clinical disease activity was measured by the SLE Disease Activity Index 2000 (SLEDAI-2K) and NP diagnoses were classified according to the 1999 ACR case definitions for NPSLE. We measured in serum of all patients anti-C1q and C1q CIC levels, the activation capacity of complement (CH50 and AP50) and different complement components (C1q, C3, C4). RESULTS: In 92 patients the symptoms were attributed to SLE. NPSLE patients consisted of 63 patients with focal NPSLE and 34 patients with diffuse NPSLE. Anti-C1q antibodies were significantly higher and CH50, AP50 and C3 were significantly lower in NPSLE patients compared with SLE patients without NPSLE. This association was specially marked for diffuse NPSLE while no differences were found for focal NPSLE. After using potential predictors, decreased C4 remained significantly associated with focal NPSLE, but only when antiphospholipid antibodies (aPL) were included in the model. C3 and AP50 were independently associated with diffuse NPSLE. When SLEDAI-2K was included in the model these two associations were lost. When individual NPSLE syndromes were analysed, psychosis and cognitive dysfunction showed significantly lower values of complement activation capacity and all complement components. No significant associations were seen for other individual NPSLE syndromes. CONCLUSION: The associations between diffuse NPSLE and anti-C1q, C3/AP50 and focal NPSLE and C4 may be explained by disease activity and the presence of aPL, respectively. The role of complement activation and complement components in lupus psychosis and cognitive dysfunction merits further research.

CD200-CD200R signaling suppresses anti-tumor responses independently of CD200 expression on the tumor.

Expression of CD200, the gene encoding the ligand for the inhibitory immune receptor CD200R, is an independent prognostic factor for various forms of leukemia predicting worse overall survival of the patients. The enhanced expression of CD200 on the tumors implies that anti-tumor responses can be enhanced by blockage of the CD200-CD200R interaction. Indeed, antibody-mediated blockade of the CD200-CD200R inhibitory axis is currently evaluated in clinical tests to boost immune responses against CD200-expressing tumors. Here, we show that mice lacking CD200, the exclusive ligand for CD200R, are resistant to chemical skin carcinogenesis. Importantly, CD200R controls tumor outgrowth independently of CD200 expression by the tumor cells themselves. Furthermore, Cd200(-/-) mice do not become tolerant to intranasally administered antigens, suggesting that tumor rejection is normally suppressed through CD200-induced immune tolerance. Decreased tumor outgrowth is accompanied by increased expression of the proinflammatory cytokines interleukin (IL)-1ß and IL-6 by the lymph node (LN) dendritic cells. During carcinogenesis, skin-draining LNs of Cd200(-/-) mice contain increased numbers of IL-17-producing FoxP3(+) cells, which preferentially home to the tumors. Thus, the CD200-CD200R axis induces tolerance to external and tumor antigens and influences the T-regulatory/Th17 cell ratio. We demonstrate for the first time that the absence of CD200R signaling inhibits outgrowth of an endogenous tumor irrespective of CD200 expression by the tumor cells. This important paradigm shift leads to a much broader applicability of CD200-blockade in the treatment of tumors.