Crosstalk between CD4 T cells and synovial fibroblasts from human arthritic joints promotes hyaluronan-dependent leukocyte adhesion and inflammatory cytokine expression in vitro.

The content and organization of hyaluronan (HA) in the extracellular matrix (ECM) have been identified as strong indicators of inflammation in joint disease, although the source and role of HA as an effector of inflammation is not clear. In this study, we established co-cultures of activated human CD4 T cells with fibroblast-like synoviocytes (FLS) from osteoarthritis (OA) and rheumatoid arthritis (RA) subjects and examined the role of HA in promoting inflammatory events. Co-cultures of RA FLS with activated CD4 T cells generated an HA-enriched ECM that promoted enhanced monocyte adhesion compared to co-cultures of OA FLS with activated CD4 T cells. In addition, both OA FLS and RA FLS co-cultures with activated CD4 T cells elicited significant increases in the expression of IL1β, TNF, and IL6, with the increase in IL6 expression most prominent in RA co-cultures. Blocking HA synthesis and accumulation with 4-methylumbelliferone reduced expression of IL6, IL1β, and TNF in both OA FLS and RA FLS co-cultures. The increase in HA synthesis in the co-cultures was mimicked by IL6 trans-signaling of FLS in the absence of CD4 T cells. Inhibition of HA synthesis blocked the increase in IL6 by RA FLS mediated by IL6 trans-signaling, suggesting that the HA synthetic pathway may be a key mediator in IL6 expression by FLS. Overall, our study indicates that HA-enriched ECM generated by co-cultures of activated CD4 T cells with FLS from human joints creates a pathogenic microenvironment by promoting adhesion of leukocytes and expression of inflammatory cytokines including IL6

Shared recognition of citrullinated tenascin-C peptides by T and B cells in rheumatoid arthritis

Tenascin-C (TNC), an extracellular matrix protein that has proinflammatory properties, is a recently described antibody target in rheumatoid arthritis (RA). In this study, we utilized a systematic discovery process and identified 5 potentially novel citrullinated TNC (cit-TNC) T cell epitopes. CD4+ T cells specific for these epitopes were elevated in the peripheral blood of subjects with RA and showed signs of activation. Cit-TNC–specific T cells were also present among synovial fluid T cells and secreted IFN-γ. Two of these cit-TNC T cell epitopes were also recognized by antibodies within the serum and synovial fluid of individuals with RA. Detectable serum levels of cit-TNC–reactive antibodies were prevalent among subjects with RA and positively associated with cyclic citrullinated peptide (CCP) reactivity and the HLA shared epitope. Furthermore, cit-TNC–reactive antibodies were correlated with rheumatoid factor and elevated in subjects with a history of smoking. This work confirms cit-TNC as an autoantigen that is targeted by autoreactive CD4+ T cells and autoantibodies in patients with RA. Furthermore, our findings raise the possibility that coinciding epitopes recognized by both CD4+ T cells and B cells have the potential to amplify autoimmunity and promote the development and progression of RA

Multifaceted immune dysregulation characterizes individuals at-risk for rheumatoid arthritis

Abstract Molecular markers of autoimmunity, such as antibodies to citrullinated protein antigens (ACPA), are detectable prior to inflammatory arthritis (IA) in rheumatoid arthritis (RA) and may define a state that is ‘at-risk’ for future RA. Here we present a cross-sectional comparative analysis among three groups that include ACPA positive individuals without IA (At-Risk), ACPA negative individuals and individuals with early, ACPA positive clinical RA (Early RA). Differential methylation analysis among the groups identifies non-specific dysregulation in peripheral B, memory and naïve T cells in At-Risk participants, with more specific immunological pathway abnormalities in Early RA. Tetramer studies show increased abundance of T cells recognizing citrullinated (cit) epitopes in At-Risk participants, including expansion of T cells reactive to citrullinated cartilage intermediate layer protein I (cit-CILP); these T cells have Th1, Th17, and T stem cell memory-like phenotypes. Antibody-antigen array analyses show that antibodies targeting cit-clusterin, cit-fibrinogen and cit-histone H4 are elevated in At-Risk and Early RA participants, with the highest levels of antibodies detected in those with Early RA. These findings indicate that an ACPA positive at-risk state is associated with multifaceted immune dysregulation that may represent a potential opportunity for targeted intervention