Evaluation of MMP-3 and IL-1RA production, and transcriptional response of IL-1RA and SIGIRR. Human fibroblast-like synoviocytes (FLS) were stimulated with pro-inflammatory cytokines either IL-1β (10 ng/ml) or a combination of IL-1β and TNF-α (10 ng/ml each), in the presence and absence of IDR peptides. The peptides were added at the time of cytokine stimulation. Tissue-culture supernatants were monitored for (a), MMP-3 production after 24-hour stimulation, or (b), IL-1RA after 48 hours, with ELISA. Transcriptional responses for (c), IL-1RA, and (d), SIGIRR, were evaluated with quantitative real-time PCR in human FLS cells stimulated with IL-1β (10 ng/ml) in the presence and absence of IDR-1002 after 2 hours. Results shown are an average of at least three independent biologic experiments performed with cells isolated from synovial tissues obtained from independent donors ± standard error (*P < 0.05). IDR, innate defence regulator; IL, interleukin; MMP-3, matrix metalloproteinase-3.