HRH4 (Histamine receptor H4) is a ubiquitous messenger molecule released from mast cells, enterochromaffin-like cells, and neurons. Its various actions are mediated by a family of histamine receptors, which are a subset of the G-protein coupled receptor superfamily. This gene encodes a histamine receptor that is predominantly expressed in haematopoietic cells. HRH4 is thought to play a role in inflammation and allergy reponses, and controls neutrophil release from bone marrow. It also plays a role in determining eosinophil shape change as well as mast cell chemotaxis and calcium mobilization. Loss of HRH4 in gastric carcinomas through deletion is also thought to play a role in cancer growth. References: J. Pharmacol. Exp. Ther. 2003. 305 (3): 1212–21. doi:10.1124/jpet.102.046581. PMID 12626656; PLoS One. 2012;7(2):e31207, PMID: 22363581