Expression of histamine H4 receptor in human osteoarthritic synovial tissue

Abstract

Osteoarthritis (OA) is a progressive non-infl ammatory disorder of the joints caused by gradual loss of cartilage and resulting in the development of bony spurt and cysts with the most common location being the knee [1]. Histamine (H) affects a variety of functions in the human body including joints. Mast cells present in the synovium are the major source of histamine [2]. They often increase in number at site of active cartilage erosion. Recently histamine has been implicated in the pathophysiological processes of OA and H receptors H1 and H2 as well as histamine decarboxylase expression were demonstrated immunohistochemically in OA chondrocytes [3]. This suggests that immuno/infl ammatory reactions are involved in the pathogenesis of OA. Histamine receptors are classifi ed into four subtypes, H1, H2, H3 and H4. The histamine H4 (HH4) receptor is a member of G-protein coupled receptors (GPCRs) and preferentially expressed on the cells of hematopoietic lineage (eosinophils, T cells, dendritic cells, basophils and mast cells) [4]. We have previously shown that the novel HH4 receptor is localized in synoviocytes found in infl amed tissue of patients with rheumatoid arthritis (RA) [5]. Here we report the studies of expression of HH4 receptor in various types of synovial cells of patients with OA.