TNF Blockade Requires 1,25(OH)2D3 to Control Human Th17-mediated Synovial Inflammation

Objectives: T helper 17 (Th17) cells from patients with early rheumatoid arthritis (RA) induce a proinflammatory feedback loop upon RA synovial fibroblast (RASF) interaction, including autocrine interleukin (IL)-17A production. A major challenge in medicine is how to control the pathogenic Th17 cell activity in human inflammatory autoimmune diseases. The objective of this study was to examine whether tumour necrosis factor (TNF) blockade and/or 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) controls Th17-mediated synovial inflammation.

Methods: Peripheral CD4+CD45RO+CCR6+ Th17 cells of patients with early RA, Th17-RASF cocultures and synovial biopsy specimens were cultured with or without 1,25(OH)(2)D(3) and/or TNFα blockade. Intracellular cytokine expression was detected by flow cytometry. Cytokine and matrix metalloprotease (MMP) production was determined by ELISA.

Results: The authors show that the 1,25(OH)(2)D(3), but not TNFα blockade, significantly suppressed autocrine IL-17A production in Th17-RASF and synovial biopsy cultures. Combining 1,25(OH)(2)D(3) and TNFα blockade had a significant additive effect compared with single treatment in controlling synovial inflammation, indicated by a further reduction in IL-6, IL-8, MMP-1 and MMP-3 in Th17-RASF cocultures and IL-6 and IL-8 expression in cultures of RA synovial tissue.

Conclusions: These data show that TNF blockade does not suppress IL-17A and IL-22, which can be overcome by 1,25(OH)(2)D(3). The combination of neutralising TNF activity and 1,25(OH)(2)D(3) controls human Th17 activity and additively inhibits synovial inflammation. This indicates more valuable therapeutic potential of activation of Vitamin D receptor signalling over current TNF neutralisation strategies in patients with RA and potentially other Th17-mediated inflammatory diseases.