Characterising bidirectional interactions between synovial fibroblasts and myeloid cells

Synovial fibroblasts and macrophages are incriminated in rheumatoid arthritis (RA) but the interactions between these cells and the roles of cellular subsets are only partially understood. To address this, fibroblasts isolated from normal, resolving arthritis, very early RA, established RA, and longer duration RA patients were co-cultured in vitro with myeloid cells; synovial fibroblast and macrophage subsets were identified, and the transcriptomes of synovial cells were analysed. Co-culture of fibroblasts and monocytes elicited an increase in IL-6 release and a reduction in CCL2/CCL4 levels. No difference in response was elicited by fibroblasts from different stages of RA. Fibroblast and macrophage markers were defined in frozen tissue sections. A synovial tissue digestion protocol was then developed and used to isolate synovial cells. Fibroblast and macrophage populations were identified and the proportions of fibroblast subsets correlated with clinical variables. Transcriptional analysis identified differentially expressed genes between fibroblast subsets and one distinct macrophage population. Analysis of previously generated transcriptome data for fibroblasts from RA stages identified cassettes of genes differentially expressed at each disease stage. This work expands previous findings on fibroblast function by beginning to assign functions to subsets and demonstrating that fibroblasts from stages of RA have distinct gene expression