The last of the four histamine receptors, H4 receptor (H4R), was identified in the year 2000. Since that time, H4R has been implicated in cellular mechanisms related to immune systems, inflammatory processes, and allergic reactions. We reported the expression of H4R in rheumatoid arthritis (RA) synovial cell cultures and human dermal tissues. In the synovial cell cultures, two specific types of cell populations, fibroblast-like and macrophage-like cells, both showed expression of H4R. We also demonstrated H4R expression in human dermal fibroblast and epidermal tissue. When investigating the effect of histamine H4R antagonists on pruritus using a mouse model, JNJ7777120, a H4R antagonist, was found to significantly reduce histamine- and substance P-induced scratching. These results suggest that H4R may be useful for treatment rheumatoid arthritis or pruritus.
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