Methotrexate preferentially affects Tc1 and Tc17 subset of CD8 T lymphocytes

Rheumatoid arthritis is considered a T-lymphocyte-mediated disease. However, studies have focussed on CD4 T-lymphocytes, ignoring CD8 T-lymphocytes despite the latter being found abundantly in the synovium. Specifically, there is little data of the effect of methotrexate, the gold-standard DMARD, on various CD8 cytokine T-lymphocyte subsets and conflicting data on CD4 subsets. In this prospective study, patients with active rheumatoid arthritis, who were 18 to 65 years of age, were treated with methotrexate (up to 25 mg per week) for 24 weeks. At baseline and 24 weeks, frequencies of CD8⁺IFNγ⁺, CD8⁺IL17⁺, CD8⁺IL4⁺, corresponding CD4 subsets and plasma levels of IFNγ, IL-12, IL-10, IL-4 and IL-17 were determined by flow cytometry. These are summarised as median (IQR = interquartile range, 25th-75th percentile) and paired data compared using Wilcoxon signed rank test. This study included 67 patients (F/M = 4:1) with rheumatoid arthritis, 57 (85%) being RF positive and 20 receiving prednisolone at baseline. Mean (± SD) dose of methotrexate at 24 weeks was 22.9 ± 3.0 mg per week. On treatment with methotrexate, there was a significant (p = 0.04) decline in CD8⁺IFNγ⁺ cells from 37.2 (IQR 19.4-60.2) to 22.7% (IQR 8.5-49.7) and a marginal increase in CD8⁺IL17⁺ cells from 0.3 (IQR 0.1-0.6) to 0.4 (IQR 0.2-1.2), p = 0.006. There was no significant change in the other subsets. There was also a significant decline in circulating levels of IL-12, IL-10 and IL-17 and marginal increase in IL-4. On evaluating by response, non-responders but not responders had a significant increase in CD8⁺IL17⁺ (p = 0.01). There is a significant decline of CD8⁺IFNγ⁺ T cells and marginal increase in CD8⁺IL17⁺ T cells after methotrexate. Change in Tc1 subset may be mediated through reduction in IL-12 levels.