HIF1A and rheumatoid arthritis: Importantly, Th1 cytokines have been demonstrated to synergise with hypoxia to induce HIF-1 protein and activity in HepG2 cells, a human hepatoma cell line [18], and to synergise with hypoxia and the hypoxia mimetic CoCl2 to induce HIF-1α mRNA and protein, respectively, in RA FLS [16,21].