These Upa concentrations, which fall within the range of Upa levels found in Upa-treated RA patients [29], had no effect on macrophage viability (Supplementary Fig. 2A), and drastically impaired the GM-CSF-induced JAK2-dependent STAT5 and ERK phosphorylation in monocytes [42] (Fig. 2A). This evidence concerns the gene JAK2 and rheumatoid arthritis.