HIF1A and rheumatoid arthritis: In contrast to the specific stabilisation of HIF-α protein occurring under hypoxic conditions, Th1 cytokines appear to act on several regulatory levels and have been reported to stimulate HIF-α mRNA synthesis and stability in macrophages and RA fibroblast-like synoviocytes (FLS) [15,16], and to induce changes in HIF-1α levels and/or transcriptional activation in a number of cell types [17,18].