THU0025 Expression of interleukin-20 and its receptors in osteoblasts and osteoclasts in bone tissue from patients with rheumatoid arthritis

Background Elevated expression of interleukin-20 (IL-20) and its receptors has been demonstrated in synovium from patients with rheumatoid arthritis (RA), and IL-20 is thought to be implicated in the pathogenesis of RA. Selective inhibition of IL-20 reduced disease activity and bone loss in rats with collagen-induced arthritis (1). In support of a role of IL-20 in bone erosion in RA, it has been demonstrated in murine cells that IL-20 stimulates expression of RANK-L in osteoblasts and RANK in osteoclasts, which leads to osteoclastogenesis and induces osteoclast activity (2) Objectives To analyse the expression and localisation of IL-20 and its receptor chains IL-20R1, IL-20R2 and IL-22R in bone samples from patients with RA using immunohistochemistry and cell identification with selected bone cell markers Methods RA bone and synovial samples were collected following joint replacement knee surgery. The bone samples were decalcified in ImmunoCal and paraffin embedded. Immunohistochemistry was performed with antibodies against IL-20 (rabbit polyclonal 2313b, Novo Nordisk), IL-20R1 (mouse monoclonal MAB11761, R&D), IL-20R2 (goat polyclonal AF1788, R&D) or IL-22R (goat polyclonal BAF2770, R&D) and immunoreactivity was visualised with DAB. Osteoblasts were identified with an antibody against RANK-L. Osteoclasts were identified using a histochemical staining for Tartrate-Resistant Alkaline Phosphatase (TRAP). The specificity of IL-20, IL-20R1, IL-20R2 and IL-22R antibodies was validated in sections of paraffin-embedded cells transfected with IL-20, or either of the two receptor complexes IL-20R1/IL-20R2 or IL-22R/IL-20R2 Results Immunohistochemical staining of paired synovial and bone tissue samples from the same patient revealed that IL-20 is present in synovial inflammatory cells located in both the lining layer and the sublining layer as previously reported (3). In the RA bone samples, a distinct localisation of IL-20 is noted in the osteoblasts lining both trabecular and cortical bone, whereas a weaker staining of IL-20 is detected in the adjacently located osteoclasts. Immunostaining with an antibody against RANK-L showed that IL-20 and RANK-L are expressed in osteoblasts in similar patterns. Expression of all three IL-20 receptor chains were analysed in bone samples from patients with RA. In serial sections stained with anti-IL-20, anti-IL-20R1 or TRAP, it was demonstrated that IL-20R1 is expressed in trabecular TRAP-positive osteoclasts, but not in the adj