Pro-inflammatory cytokines and chemokines play critical roles in rheumatoid arthritis (RA). Recent studies have addressed the role of toll-like receptors (TLR)s in the development and progression of RA. An important role of various TLRs in the animal model of arthritis has been demonstrated. TLR4 and endogenous TLR4 ligands such as hyaluronan and heat shock protein (HSP)22 are highly expressed in synovial tissue from RA patients compared with healthy donors further implicating TLRs in RA pathogenesis. However the signaling pathways that regulate endogenous TLR4 ligands-induced TLR activation in RA are not fully understood. Recent studies demonstrated that adaptor proteins [unreadable]-arrestin 1 and 2 associating with TRAF6, I[unreadable]B[unreadable], and NF[unreadable]B1p105 negatively regulate TLR signaling. Our data demonstrated for the first time that [unreadable]-arrestin 2 knockout (KO) mice exhibited more severe arthritis in the collagen antibody-induced arthritis (CAIA) model compared to wild type (WT) mice. Furthermore, we observed that [unreadable]-arrestin 1 and 2 expression are increased in splenocytes and fibroblast-like synoviocytes (FLS) in the collagen-induced arthritis (CIA) mice compared to the control mice. It was also demonstrated that LPS- and the endogenous TLR4 ligand low molecular weight hyaluronan (LMW-HA)- induced TNF[unreadable], IL-6 and IL-10 production were augmented in splenocytes from [unreadable]- arrestin 2 KO mice compared to WT mice. These findings led us to propose the hypothesis that up-regulation of [unreadable]-arrestin 1 and 2 expression suppresses inflammation in collagen-induced arthritis by negative regulation of inflammatory cell responses. The specific aim is to investigate the role of [unreadable]-arrestin 1 and 2 as negative regulators of the inflammatory response in collagen-induced arthritis. [unreadable]-arrestin 1 and 2 expression in splenic macrophages, CD4+ and CD8+ T lymphocytes, B lymphocytes, dendritic cells (DC)s, polymorphonuclear leukocyte (PMN)s and FLS correlation to the disease severity in the mouse CIA model will be examined. Once the specific immune cells that exhibit altered expression of [unreadable]-arrestins are identified, the role of [unreadable]-arrestin 1 and 2 expression on activation of these cells will be examined using the lentiviral expression system to overexpress [unreadable]-arrestins or knock down [unreadable]-arrestins with RNAi. Understanding [unreadable]-arrestins-dependent signaling pathways that regulate pro- and anti-inflammatory gene expression will provide novel insights into the pathogenesis of RA from which innovative targeted interventions can evolve.