Background/Purpose: CD8 T cells comprise 40 % of all T cells in the synovial compartment and are detectable in he preclinical stages as well. They have been shown to play an important role in rheumatoid arthritis pathogenesis. They can be divided by cytokine production into CD8+IFNγ+, CD8+IL4+ and CD8+IL17+. Methotrexate is the gold standard benchmark DMARD used in therapy of RA. The effect of methotrexate on these circulating CD8 T cell subsets has not been well described.

Methods: Patients who were 18 to 65 years of age and having active rheumatoid arthritis (fulfilling the ACR 1987 criteria) were treated with methotrexate for 24 weeks. Methotrexate was started at 15 mg per week, and escalated at 5 mg per month to a maximum of 25 mg per week. Disease activity was measured using the disease activity score and response to treatment assessed by EULAR criteria. At 0 (baseline) and 24 weeks (post methotrexate), PBMCs were isolated using density gradient centrifugation and stimulated with PMA /Ionomycin (with Brefeldin) for 5.5 hours. Surface staining was done using anti CD3/ anti CD8 and intracellular cytokine staining with tagged antibdoies to IFNγ, IL17 and IL4. 30,000 events were acquired and in CD3+ gate, frequencies of CD8+INFγ+ cells, CD8+IL17+ and CD8+IL4+ were determined. Cytokine bead array was used to determine levels of IFNγ, IL-12, IL-10, IL-4 and IL-17 in plasma at 0 and 24 weeks. Cell frequencies and cytokine levels at baseline and 24 weeks were described by using median (IQR=interquartile range, 25th- 75th percentile) and compared using non-parameteric paired test (wilcoxon signed rank).

Results: This study included 67 patients (F:M=4:1) with rheumatoid arthritis, 57 (85%) being RF positive and 20 receiving prednisolone at baseline. The mean dose of methotrexate at 24 weeks was 22.9±3.0 mg per week. DAS28 declined from 5.9±1.1 to 4.8±1.0 (p<0.001). CD8+IFNγ+ cells declined from 37.2 (IQR 19.4-60.2) to 22.7% (IQR 8.5-49.7), p=0.04 and there was 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. In non-responders, there was a significant increase in CD8+IL17+ (p=0.01) that was not seen in responders. There was a significant decline in the circulating levels of IL-12 [519(IQR 40.4-2336.1), 124.7(IQR 23.5-771.9) pg/ml, p<0.001) and IL-17 but increase in IL-4 with treatment.

Conclusion: Methotrexate leads to changes in circulating CD8 subsets, predominantly decline of the CD8+IFNγ+ subset, that may be explained due to reduction in the polarising cytokine IL-12 and increase in IL-4. This may be one of the mechanisms responsible for the effect of methotrexate in RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/decline-in-cd8ifn%ce%b3-subset-but-rise-in-cd8il17-on-methotrexate-treatment-in-rheumatoid-arthritis/