Immunopharmacology and InflammationAnti-IL-6 receptor antibody suppressed T cell activation by inhibiting IL-2 production and inducing regulatory T cells
Introduction
Rheumatoid arthritis is an autoimmune inflammatory disease characterized by symmetric polyarthritis and progressive structural joint damage. Activated T cells are abundantly observed in the inflamed joints of rheumatoid arthritis patients (Fox et al., 1982, Hemler et al., 1986). Moreover, anti-rheumatic drugs, such as methotrexate, tacrolimus and abatacept, that potently inhibit T cell activation, are effective in the treatment of rheumatoid arthritis patients (Olsen & Murray, 1989, Yoshimura et al., 1989, Linsley et al., 1991). These lines of evidence strongly suggest that activated T cells play crucial roles in the progression and maintenance of arthritis in rheumatoid arthritis patients.
Drugs that block the signalling pathways of pro-inflammatory cytokines such as tumour necrosis factor-α (TNFα) and interleukin (IL)-6 also dramatically reduce disease activity and halt the progression of joint destruction in rheumatoid arthritis patients with an inadequate response to conventional disease-modifying anti-rheumatic drug therapy (Maini et al., 1999, Weinblatt et al., 1999, Nishimoto et al., 2004). TNFα augments the inflammatory response by inducing inflammatory mediators such as prostaglandins, cytokines and chemokines, and expression of adhesion molecules (Feldmann et al., 1992). This suggests that the mechanism of action of TNFα blockers includes the suppression of the inflammatory response, but it has not been clear whether TNFα blockade inhibits T cell activation.
IL-6 also induces inflammatory mediators and adhesion molecules (Suzuki et al., 2010). Moreover, IL-6 promotes IL-4-induced T helper 2 (Th2) differentiation and inhibits IL-12-induced Th1 differentiation (Diehl and Rincon, 2002). Furthermore, IL-6 induces Th17 differentiation in the presence of transforming growth factor (TGF)-β and inhibits the induction of TGF-β-induced regulatory T cells (Bettelli et al., 2006). The therapeutic effects of an anti-IL-6 receptor antibody such as tocilizumab may therefore be the result of inhibiting any combination of the above actions of IL-6, but again, the impact of IL-6 blockade on T cell activation has not been fully understood.
We conducted the present study to shed light on the question of whether anti-IL-6 receptor antibody or anti-TNFα antibody suppresses the activation of stimulated T cells in two in vitro T cell-activation systems. One system consisted of spleen cells stimulated by anti-CD3 antibody, and the other system consisted of purified splenic CD4 T cells stimulated by both anti-CD3 antibody and anti-CD28 antibody. Using these two systems, we examined and compared the effects of anti-IL-6 receptor antibody, anti-TNFα antibody and cytotoxic T lymphocyte antigen 4 fusion protein (CTLA4-Fc) as a positive control on T cell activation.
Section snippets
Reagents
Anti-mouse IL-6 receptor antibody (MR16-1) was prepared in our laboratories (Okazaki et al., 2002). Anti-mouse TNFα antibody (clone TN3-19.12) and mouse CTLA4-Fc were purchased from BD Pharmingen (San Diego, CA) and R&D systems (Minneapolis, MN), respectively. Anti-CD3 antibody and anti-CD28 antibody were purchased from Cedarlane Laboratories (Ontario, Canada) and BD Pharmingen, respectively.
Animals
Female BALB/c mice were purchased from Charles River Japan (Yokohama, Japan). The mice were specific
Effects on thymidine uptake
In the study using whole spleen cells, anti-TNFα antibody had no effect on thymidine uptake, whereas CTLA4-Fc inhibited thymidine uptake in a concentration-dependent manner (almost completely at 1 μg/ml). Anti-IL-6 receptor antibody also significantly inhibited thymidine uptake, but the degree of inhibition did not increase with increasing concentration, and never exceeded approx. 30% (Fig. 1A).
Similar results were obtained in CD4 T cells, except that CTLA4-Fc had no effect in these cells (Fig. 1
Discussion
There is no doubt that activated T cells are involved in the pathogenesis of rheumatoid arthritis. The dramatic therapeutic effects of anti-cytokine therapies such as anti-TNFα antibodies and the anti-IL-6 receptor antibody raise the question as to whether these treatments inhibit the activation of T cells in rheumatoid arthritis. In the present study, we examined the effects of anti-IL-6 receptor antibody, anti-TNFα antibody and CTLA4-Fc on T cell activation in two experimental systems: spleen
Conclusions
In conclusion, our results show that anti-IL-6 receptor antibody significantly (but only partially) suppressed the T cell receptor signalling-induced activation of CD4 T cells. They also suggest that anti-IL-6 receptor antibody achieved this suppression by causing partial inhibition of IL-2 production and the induction of regulatory T cells. In stark contrast, anti-TNFα antibody showed no evidence of any impact on T cell activation. Extrapolating these results to the clinical treatment of
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