Rheumatoid arthritis fibroblast-like synoviocytes co-cultured with PBMC increased peripheral CD4(+) CXCR5(+) ICOS(+) T cell numbers.

'Circulating' T follicular helper cells (Tfh), characterized by their surface phenotypes CD4(+) chemokine receptor 5 (CXCR5)(+) inducible co-stimulatory molecule (ICOS)(+) , have been identified as the CD4(+) T cell subset specialized in supporting the activation, expansion and differentiation of B cells. Fibroblast-like synoviocytes (FLS) are critical in promoting inflammation and cartilage destruction in rheumatoid arthritis (RA), and the interaction between FLS and T cells is considered to facilitate FLS activation and T cell recruitment. However, it remains unknown whether RA-FLS co-cultured with activated peripheral blood mononuclear cells (PBMC) has immunoregulatory effects on peripheral Tfh. In the present study, we co-cultured RA-FLS with or without anti-CD3/CD28-stimulated PBMC. The results showed that RA-FLS co-cultured with stimulated PBMC could increase the numbers of CD4(+) CXCR5(+) ICOS(+) T cells of RA PBMC possibly via the production of interleukin (IL)-6, a critical cytokine involved in the differentiation of Tfh cells. We also observed increased reactive oxygen species (ROS) levels in the co-culture system of RA-FLS and PBMC. The percentage of CD4(+) CXCR5(+) ICOS(+) T cells was decreased when ROS production was inhibited by N-acetyl-L-cysteine (NAC), a specific inhibitor which can decrease ROS production. In addition, we showed that the higher levels of tumour necrosis factor (TNF)-α and IL-1β in the co-culture system and the blocking of TNF receptor 2 (TNF-R2) and IL-1β receptor (IL-1βR) both decreased the numbers of CD4(+) CXCR5(+) ICOS(+) T cells. Our study reveals a novel mechanistic insight into how the interaction of RA-FLS and PBMC participates in the RA pathogenesis, and also provides support for the biologicals application for RA.