Abstract
Objective: Human IL-18BP gene encodes at least four distinct isoforms (IL18BPa-d) derived by alternative splicing. Their presence in RA local inflammation is not yet examined. This study aimed to determine the messenger transcript and protein levels of IL-18BP isoforms in patients with Rheumatoid Arthritis (RA). Materials: The study comprises 65 rheumatic patients, 22 Osteoarthritis (OA), and 40 sex and age matched normal controls (NC). Peripheral blood mononuclear cells (PBMCs) and synovial fluids mononuclear cells (SFMCs) were prepared by using Ficoll-Hypaque procedure. The expression and presence of different isoforms were determined by using real-time PCR and ELISA respectively. Results: IL-18BP messenger transcript has been extremely expressed in synovial fluids (SF) and synovial tissues (ST) of RA patients compared to OA patients (p < 0.001). IL-18BP auto-antibodies were noticed in RA plasma and SF (41.7%; 37.9%), in OA-SF (9.0%), and in plasma of NC (4.0%). Comparable to different isoforms, isoform "c" showed significant local expression (p < 0.001) in RA-SFMC and systematic expression (p < 0.001) between RA-and NC-PBMCs, isoform "a" was least expressed. Isoform "c" and "d" proteins were solely detected by western blot in RA. Conclusions: This study emphasizes the local existence of isoform "c" and "d", and the possible presence of autoantibodies against IL-18BPa in RA patients, which made a pea for further investigation, putting in place their actual role.