Upregulation of antigen presentation function and inflammation in chondrocytes by induction of proteoglycan aggrecan peptides (P16-31 and P263-280).

OBJECTIVES: A central hallmark of osteoarthritis (OA) is cartilage destruction. Chondrocytes not only control cartilage metabolism, but are capable of immunogenic responses. The role of chondrocytes in the pathogenesis of OA is still unclear. In this study, we aimed to determine the immunological role of chondrocytes in response to proteoglycan aggrecan (PG) peptides. METHODS: Human chondrocytes were isolated from cartilage of knee OA patients undergoing knee arthroplasty and stimulated with proteoglycan aggrecan peptides in the presence of IFNγ. Antigen presentation markers, co-stimulatory molecules, cytokine production, gene expression and antigen presentation to T cells were evaluated. RESULTS: Our results show that IFNγ was required for the expression of MHC class I and II. However, stimulation with PG peptides P16-31 and P263-280, but not P2379-2394, increased expression level of co-stimulatory molecules (CD80 and CD86) and IL-6, IL-8 and TNFα production. This upregulation was seen in chondrocytes to nearly comparable levels of professional antigen-presenting cells. A similar pattern of gene expression was observed between P16-31 and P263-280 peptide stimulation on chondrocytes and this was different from P2379-2394 peptide treatment. Co-culture with autologous T cells revealed signi cant proliferation of cells when stimulating with the P263-280 peptides. CONCLUSIONS: Our study shows that human chondrocytes display unique features of antigen presentation. Their ability to process certain proteoglycan aggrecan peptides, in which these molecules are synthesised by the cartilage themselves render the possibility of a role for "self-antigens" in the immunopathogenesis of OA.

The infrapatellar fat pad produces interleukin-6-secreting T cells in response to a proteoglycan aggrecan peptide and provides dominant soluble mediators different from that present in synovial fluid.

OBJECTIVE: The purpose of this study was to investigate the effects of osteoarthritis (OA) peripheral blood mononuclear cell (PBMC) -stimulating proteoglycan aggrecan peptides on T cells present in infrapatellar fat pads (IPFPs) and synovial tissues, and to correlate these findings with mediators present in synovial fluid of OA patients. METHODS: We tested for interleukin-6 (IL-6) -producing T cells in IPFPs of patients with knee OA using ELISPOT. Cytokine and cytotoxic mediator production from OA PBMCs, IPFPs, synovial tissues, and synovial fluids in response to proteoglycan aggrecan peptides were quantified by cytometric bead array. Patterns of cytokine and cytotoxic mediator production were analyzed and compared. RESULTS: T cells from IPFPs elicited strong responses towards the p263-280 peptide by secreting IL-6. In addition, there was a trend that the p263-280 peptide stimulated higher production of cytokines/cytotoxic mediators than other proteoglycan aggrecan peptides, although this was not statistically significant. In patients with knee OA, a group of cytotoxic mediators (sFas, perforin, granzyme A, and granulysin) and IL-6 were detectable at high levels from the synovial fluid. In addition, inflammation in patients with knee OA was more pronounced in joint-surrounding tissues than levels in circulating peripheral blood. CONCLUSION: Our data suggest that T cells responding to the p263-280 peptide contribute to the secretion of various soluble mediators that are found within the synovial fluid. We also identified potential new candidates that may serve as biomarkers of knee OA.