A novel inhibitory pathway of synovial inflammation exerted by glucocorticoids and tumour necrosis factor inhibitors via lymphocyte activation gene-3 up-regulation: an ex vivo study

Objective: To investigate the impact of glucocorticoids (GCs) and anti-rheumatic drugs on lymphocyte activation gene-3 (LAG-3) and on programmed cell death-1 (PD-1) expression by synovial and peripheral cells ex vivo. Methods: Synovial fluid mononuclear cells (SFMCs) from psoriatic arthritis (PsA, n ¼ 26) and rheumatoid arthritis (RA, n ¼ 13) patients, synovial fluid cells (SFCs) from osteoarthritis (OA, n ¼ 5) patients and peripheral blood mononuclear cells (PBMCs) of healthy donors (n ¼ 14) were co-cultured with GCs, glucocorticoid receptor antagonist RU486, methotrexate (MTX) and biologics. LAG-3 and PD-1 expression on immune subsets were analysed by flow cytometry. Results: GCs in PsA inhibited SFMC growth vs medium [2.3 (0.4) × 10⁵ vs 5.3 (0.7) × 10⁵, respectively, P < 0.01] and markedly up-regulated CD14^þLAG-3^þ cells [11.7 (2.4)% vs 0.8 (0.3)%, P < 0.0001, respectively], but not CD3^þLAG-3^þ and CD14^þPD-1^þ cells. MTX had no effect on CD14^þLAG-3^þ cells [0.7 (0.3)%]. The TNF inhibitors infliximab (IFX) and etanercept, but not IL-12/23 inhibitor, up-regulated CD14^þLAG-3^þ cells vs medium [2.0 (0.6)% and 1.6 (0.4)% vs 0.5 (0.1)%, P < 0.03, respectively]. SFMC growth inhibition by GC in both PsA and RA correlated with CD14^þLAG-3^þ cell up-regulation (r ¼ 0.53, P ¼ 0.03). RU486 inhibited GC-induced CD14^þLAG-3^þ cells up-regulation in a dose-dependent manner compared with GC alone [5 µM 5.3 (1.2)% and 50 µM 1.3 (0.5)% vs 7.0 (1.4)%, P < 0.003], but had no significant effect on CD14^þLAG-3^þ cells co-cultured with IFX. GCs in healthy donors’ PBMCs up-regulated the immune subsets CD3^þLAG-3^þ, CD14^þLAG-3^þ and CD14^þPD-1^þ cells. Conclusion: This study proposes a novel regulatory mechanism of GCs and of TNF inhibitors mediated by LAG-3 up-regulation in synovial cells and PBMCs. LAG-3 modulation may be a promising target for development of novel therapies for inflammatory arthritis.