In peripheral tissues such as the spleen, thymus and bone marrow its levels of expression are altered in response to inflammatory stimuli.16 Several lines of evidence indicate that the H4R plays a key role in both pulmonary and intestinal inflammatory diseases (asthma, colitis), pruritus, allergies and other immunological disorders, which has led to the therapeutic development of novel H4R ligands. The gene discussed is HRH4; the disease is Pruritus.