To compare the expression of leucocyte immunoglobulin-like receptors (LILRs) also known as ILTs and LIRs in rheumatoid arthritis (RA) synovial membrane before and after treatment with disease-modifying anti-rheumatic drugs (DMARDs) and investigate regulation of LILR-expression and function in vitro.
A study was performed on serial synovial biopsies obtained from 10 RA patients before and after treatment with DMARDs. Expression of the activating LILRA2 (ILT1 or LIR-7) and inhibitory LILRB2 (ILT4 or LIR-2) and LILRB3 (ILT5 or LIR-3) was evaluated by immunohistochemical staining, and quantified by a validated scoring system. Peripheral blood mononuclear cells and in vitro derived macrophages were used to determine effects of DMARDs on expression and function of LILRs.
Abundant expression of LILRB2, B3 and A2 was found in synovial tissue of all patients before treatment. Number of inflammatory cells expressing both inhibitory and activating LILRs dramatically decreased in patients who responded to treatment, but remained high in those who did not. However, treatment of macrophages with DMARDs in vitro did not down-regulate LILR expression. On the other hand, reduction in LILR expression in RA synovia was associated with decreased inflammatory infiltrates in those who responded to treatment. Cross-linking of LILRA2 on macrophages caused substantial production of tumour necrosis factor (TNF-alpha) in a dose- and time-dependent manner that was strongly inhibited by dexamethasone.
We show that expression of LILRs in RA synovium was significantly reduced only in patients who responded to treatment. However, clinical responses may not be due to direct effects of DMARDs on LILR expression but due to partial inhibition of LIRA2-mediated TNF-alpha production by steroids leading to suppression of inflammation.