HRH4 and Alzheimer disease: To investigate the effects of histamine on IL-10-induced CCL18 mRNA expression in cells from healthy control persons versus cells from AD patients, human monocyte-derived M2 macrophages obtained from both groups were stimulated for 24 h with IL-10 and after 24 h with histamine and selective agonists targeting the H1R, H2R and H4R for an additional 24 h.