**2.1 Synovial fibroblasts (SF)**

Proliferation and infiltration of SF is the key trigger for disease progression in RA. Under normal conditions fibroblasts are responsible for maintaining tissue homeostasis by modulating the inflammatory response [15]. Transcription factors like activator protein-1 and NF-κB, responsible for proliferation, activation, differentiation of fibroblasts, expression of MMPs, other matrix-degrading enzymes like cysteine proteases and aggrecanases have been observed in the synovium [5]. The genetic analysis of synovium would be useful for biological therapy as synovial tissue has a robust immune-inflammatory gene expression [16].
