Background Interleukin-20 (IL-20) signals via the IL-20R1/IL-20R2 and IL-20R2/IL-22R1 heterodimeric receptor complexes. Elevated expression of IL-20 has been demonstrated in synovial tissue from patients with rheumatoid arthritis (RA). In the rat CIA model blockade of IL-20 has been shown to reduce disease activity. Neutralisation of IL-20 may provide a new beneficial therapy for patients with RA

Objectives To analyse the expression and localisation of IL-20 and the receptor chains IL-20R1, IL-20R2 and IL-22R in RA synovial tissue biopsies using immunohistochemistry and double-immunofluorescence

Methods Synovial biopsies from patients with RA or osteoarthritis were obtained during joint replacement surgery or synovectomy and normal, non-inflamed synovial samples were obtained during impingement surgery. Immunohistochemistry and double-immunofluorescence staining on paraffin-embedded sections using microwave treatment between the primary antibodies and tyramide streptavidin amplification were performed with antibodies for 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 antibodies recognising T-cell markers CD3, CD4 and CD8; DC-markers CD1a, CD11c, CD123, CD83 and CD303; the macrophage marker CD68; endothelial marker CD31 and the fibroblast-like synoviocyte marker CD55. The specificity of primary antibodies was validated in sections of cells transfected with IL-20, or one of the two receptor complexes IL-20R1/IL-20R2 and IL-22R/IL-20R2

Results Immunohistochemical staining revealed that IL-20 was present in inflammatory cells in RA synovial biopsies compared with low or no immunoreactivity in normal or OA synovium as previously reported (2). In RA joint replacement and synovectomy tissues IL-20–positive (+) cells were identified in both the areas of the lining layer and the sublining layer. IL-20+ cells located in the area of the lining layer co-stained with CD1a and CD4, which indicates that IL-20 is located in a subpopulation of immature DCs. Interestingly, in the RA samples obtained during synovectomy the IL-20+ cells in lymphoid aggregates co-stained with the T-cell marker CD3. All three IL-20 receptor chains were expressed in both the lining and the sublining layers, and were all co-localised with CD31+ endothelial cells. Subpopulations of IL-20R1+ and IL-20R2+ cells were observed in the lining layer and co-localised with either CD68 or CD55 reflecting a heterogenic pattern where both macrophage-like and fibroblast-like synoviocytes may be responsive to IL-20

Conclusions IL-20 was present in CD1a+ and CD4+ immature DCs and in infiltrating T cells in the sublining layer of RA synovectomy samples. The localisation of the IL-20 receptor chains in endothelium and different subsets of synoviocytes in RA synovial tissue supports that IL-20 is a relevant target in patients with RA. A neutralising human anti-IL-20 monoclonal antibody, NNC0109-0012, is being studied as a therapy in patients with RA

1. Hsu et al, Arthritis Rheum. 62:3311-21, 2010.

2. Rømer et al, Abstract #FRI0079 at EULAR, 2009

Disclosure of Interest J. Rømer Shareholder of: Novo Nordisk A/S, Employee of: Novo Nordisk A/S, M. Jackerott Shareholder of: Novo Nordisk A/S, Employee of: Novo Nordisk A/S, J. Mandelbaum Shareholder of: Novo Nordisk A/S, Employee of: Novo Nordisk A/S, M. Andersen Employee of: Novo Nordisk A/S, N. Nielsen: None Declared, H. Bliddal: None Declared