Abstract
Objective
To study the regulation of interleukin‐18 binding protein (IL‐18BP) production by rheumatoid arthritis (RA) or control peripheral blood mononuclear cells (PBMCs) and by RA synovial tissue cells, and to compare the levels of IL‐18BP messenger RNA (mRNA) expression in whole blood from RA patients and controls.
Methods
Unstimulated or phytohemagglutinin and phorbol myristate acetate (PHA/PMA)–stimulated PBMCs from 10 RA patients and 12 healthy controls and unstimulated or PHA/PMA‐stimulated synovial tissue cells from 8 RA patients were cultured with or without IL‐12 (1 ng/ml) and IL‐18 (5 ng/ml) alone or in combination. IL‐18BP and interferon‐γ (IFNγ) levels in supernatants were measured by enzyme‐linked immunosorbent assay. Levels of IL‐18BP and IFNγ mRNA expression in whole blood samples from 22 RA patients and 12 healthy controls were determined by quantitative reverse transcriptase–polymerase chain reaction.
Results
IL‐12 decreased the basal levels of IL‐18BP production by freshly isolated RA or control PBMCs, but increased those of synovial cells or PHA/PMA‐stimulated PBMCs. IL‐18 alone had no direct effect on IL‐18BP production by PBMCs or RA synovial cells, with or without stimulation. Unstimulated whole blood samples from RA patients showed lower levels of IL‐18BP mRNA expression than those from healthy controls.
Conclusion
The production of IL‐18BP in response to IL‐12 and IL‐18 was regulated differently in blood and synovial cells. The difference appears to be related to the level of cell activation.