Despite the claims of Elsen et al. (1), there are now over 45 articles that have measured human irisin, using a variety of immunoassays with independently derived antibodies, as well as mass spectrometry. Surely the existence of human irisin in blood must now be considered a closed issue. With regard to irisin function on human fat cell cultures, the ability to brown cells from multiple depots has never, to our knowledge, been accepted as a criterion for effects of any agent on adipose tissues.
These authors should know that irisin works mainly on beige fat cells and their precursors in mice (2), so we would indeed expect depot-selective differences in humans.
Duality of Interest. B.M.S. is a consultant to and shareholder in Ember Therapeutics. No other potential conflicts of interest relevant to this article were reported.