Effector function of type II collagen–stimulated T cells from rheumatoid arthritis patients: Cross‐talk between T cells and synovial fibroblasts

To investigate the effector function exerted by type II collagen (CII)–stimulated T cells on rheumatoid arthritis (RA) fibroblast‐like synoviocytes (FLS), and to determine their contribution to RA pathogenesis.

We used enzyme‐linked immunosorbent assays to measure the levels of interleukin‐15 (IL‐15), tumor necrosis factor α (TNFα), and IL‐18 production by FLS that were cocultured with antigen‐activated T cells. Likewise, we analyzed the levels of interferon‐γ (IFNγ) and IL‐17 production by RA T cells coincubated with FLS. To investigate the cross‐talk between CII‐stimulated T cells and RA FLS, we examined the effect of using a transwell membrane to separate T cells and FLS in a culture chamber, as well as the effect of adding an antibody to block CD40 ligation.

The levels of IL‐15, TNFα, IFNγ, and IL‐17 were all significantly increased in the serum of RA patients compared with normal control serum. Among the patients, the group with a stronger T cell proliferation response to CII showed higher levels of these inflammatory mediators. When coincubated with RA FLS, these T cells induced the production of IL‐15, TNFα, and IL‐18 by FLS with an intensity that increased in proportion to the duration of CII stimulation. T cells, in turn, responded to FLS stimulation by secreting higher amounts of IL‐17 and IFNγ in coculture. Interestingly, T cells that were activated by CII for longer periods of time showed stronger induction of these cytokines. The cross‐talk between T cells and FLS appeared to require direct cell–cell contact as well as CD40 ligation, at least in part.

Through repeated stimulation by CII, RA synovial T cells became trained effector cells that induced the production of proinflammatory mediators by FLS, while in the process the T cells becoming more sensitized to the activation signal from FLS.