Fischer et al. (2017) recently reported that interleukin-4 (IL-4) does not increase adipose thermogenesis and that activated macrophages do not synthesize catecholamines. These findings are unexpected because IL-4 activation of macrophages has been proposed to have a pivotal role in cold-induced thermogenesis by stimulating macrophage catecholamine production to recruit thermogenic beige or brite fat.