RESUMO
Objective: To investigate the expression and function of interleukin-18 [IL-18] protein in synovial tissue [ST] of patients with rheumatoid arthritis [RA]
Methodology: IL-18 and IL-18 receptors [IL-18R] mRNA expression was detected by reverse transcription-polymerase chain reaction [RT-PCR]. Expression of IL-18 at protein level was analyzed by western plotting technique. Cytokines; [IL-18 and interferon-gamma [IFN-gamma]] in culture supernatants from ST cell organ and synovial cultures were measured by ELISA. Samples: The ST samples were taken from 29 RA patients and 23 osteoarthritis patients [OA] were included as controls
Results: Using RT-PCR, for RAST and OAST, mRNA expression of IL-18 was detected in 26 out of 29 [89.7%] RA patients and in 11 out of 23 [47.8%] OA controls. However, mRNA expression of IL-18 R alpha and beta chains were detected in 26 and 24 out of 29 [89. 7% and 82.8%] RA patients, respectively. OAST did not express ,nRNA of alpha and beta chains of IL- 18 R. In vitro study of IL-18 production by ST showed significantly higher levels in RA compared to that of OA patients [p<0.005]. Western blotting revealed that RAST expressed IL-18 more abundantly than OAST [p<0.02]. Only IL-12, but not IL-18, stimulates IFN -gamma production by RAST cells [M +/- SD=230 +/- 17 pg/ml]. However, when IL-12 was combined with IL-18, they could significantly stimulate IFN -gamma production by RAST cells [M +/- SD= 612-B5 pg/ml]. OAST cells did not respond to neither to IL- 12 alone nor when combined to IL-18
Conclusion: IL-18 is expressed in RA synovia and contributes to the production of IFN -gamma by the infiltrating T-cells. These cytokines could play a role in the synovial inflammation in RA patients