Expression of interleukin-12 in synovial tissue from patients with rheumatoid arthritis

Objective. To examine the importance of interleukin-12 (IL-12) as a factor in the interferon-gamma (IFN gamma)-dominant T cell cytokine response in the synovial tissue of patients with rheumatoid arthritis (RA). Methods. The expression of IL-12 in synovial tissue samples from patients with chronic RA (greater than or equal to 2 years) was compared with that in samples from osteoarthritis (OA) patients by detection of IL-12 p40 messenger RNA (mRNA) using reverse transcriptase-polymerase chain reaction, measurement of IL-12 p70 protein in culture supernatants of tissue cells by immunoassay, and immunostaining of tissue sections with anti-IL-12 p70. The production of IFN gamma by RA synovial tissue cells cultured with or without IL-12 was determined, In addition, T cells were obtained 14 days after culturing RA synovial tissue cells with IL-2 alone or with IL-2 plus IL-12, neutralizing anti-IL-12, or IL-4, and cytokine patterns (i.e., IFN gamma and IL-1 levels) were determined by stimulating cells for 24 hours with anti-CD3 plus phorbol myristate acetate. Results. Synovial tissues from Ri patients more strongly expressed IL-12 p40 mRNA than did OA tissues. Dissociated tissue cells from 21 of 37 RA patients spontaneously released detectable amounts of IL-12 p70 (greater than or equal to 12.5 pg/ml) in culture, whereas production of IL-12 by OA tissues was limited. By immunohistochemical analysis, IL-12-producing cells were localized mainly in the sublining layer of RA synovium, and mostly expressed the CD68 antigen. Levels of IFN gamma production by RA synovial tissue cells were potently and selectively enhanced by IL-12. The ability of IL-2-expanding synovial T cells to produce IFN gamma was augmented by costimulation with IL-12 and diminished by anti-IL-12, while it was not affected by IL-4. Conclusion. These data suggest that IL-12, produced mainly by macrophage-lineage cells, may be involved in IFN gamma-dominant cytokine production by infiltrating T cells in joints with chronic RA.