IL13 and mastocytosis: The authors found that the presence of the IL4R p.Q576R missense was also associated with a lower MC burden as determined both by the extent of clinical disease and by circulating levels of surrogate disease markers (i.e., tryptase and soluble CD117) and suggested that increased IL-4 and/or IL-13 signaling may limit tissue MC numbers in patients with mastocytosis [26].