ARTHRITIS & RHEUMATISM Vol. 63, No. 9, September 2011, pp 2617–2629 DOI 10.1002/art.30460 © 2011, American College of Rheumatology Blockade of NKG2D Ameliorates Disease in Mice With Collagen-Induced Arthritis A Potential Pathogenic Role in Chronic Inflammatory Arthritis Anna K. Andersson, 1 Percy F. Sumariwalla, 1 Fiona E. McCann, 1 Parisa Amjadi, 1 Chiwen Chang, 2 Kay McNamee, 1 Ditte Tornehave, 3 Claus Haase, 3 Henrik Agersø, 3 Vibeke W. Stennicke, 3 David Ahern, 1 Birgitte Ursø, 3 John Trowsdale, 2 Marc Feldmann, 1 and Fionula M. Brennan 1 Objective. To assess the role of the activating receptor NKG2D in arthritis. Methods. Levels of NKG2D and its ligands were determined by fluorescence-activated cell sorting, real- time polymerase chain reaction, and immunohistochem- istry in rheumatoid arthritis (RA) synovial membrane tissue and in paw tissue from arthritic mice. Arthritis was induced in DBA/1 mice by immunization with type II collagen, and mice were treated intraperitoneally with a blocking anti-NKG2D antibody (CX5) on days 1, 5, and 8 after clinical onset and were monitored for 10 days. Results. We demonstrated expression of NKG2D and its ligands on human RA synovial cells and ex- tended this finding to the paws of arthritic mice. Ex- pression of messenger RNA for the NKG2D ligand Rae-1 was up-regulated, and NKG2D was present pre- dominantly on natural killer (NK) and CD4 T cells, in arthritic paw cell isolates. NKG2D was down-modulated during the progression of collagen-induced arthritis (CIA). NKG2D expression in arthritic paws was dem- onstrated by immunohistochemistry. Blockade of NKG2D ameliorated established CIA, with significant reductions in clinical scores and paw swelling. Histo- logic analysis of arthritic joints from anti-NKG2D– treated mice demonstrated significant joint protection, compared with control mice. Moreover, anti-NKG2D treatment significantly reduced both interleukin-17 pro- duction from CD4 T cells in arthritic paws and splenic NK cell cytotoxic effector functions in vivo and in vitro. Conclusion. Our findings indicate that blockade of NKG2D in a murine model and in human explants has beneficial therapeutic potential that merits further investigation in RA. Natural killer (NK) cells are lymphocytes of the innate immune system with both cytotoxic and cytokine- producing effector functions, regulated by a repertoire of cell receptors, including activating receptors NKG2D, CD16 (Fc receptor III), NKp30, NKp44, and NKp46; killer cell immunoglobulin-like receptor; and the inhib- itory receptors CD94/NKG2A and LY49 (mouse) (for review, see ref. 1). The role of NK cells in the defense against infections and cancer has been studied exten- sively (1), but their role in autoimmunity and chronic Supported by research funding from Novo Nordisk, Den- mark, an Arthritis Research Campaign core grant provision, and biomedical research center funding from the National Institute for Health Research. 1 Anna K. Andersson, PhD, Percy F. Sumariwalla, PhD, Fiona E. McCann, PhD, Parisa Amjadi, MSc, Kay McNamee, BSc, David Ahern, PhD, Marc Feldmann, MBBS, PhD, FRS, Fionula M. Brennan, PhD, FRCPath: Imperial College London, London, UK; 2 Chiwen Chang, PhD, John Trowsdale, PhD: University of Cambridge, Cam- bridge, UK; 3 Ditte Tornehave, PhD, Claus Haase, PhD, Henrik Agersø, PhD, Vibeke W. Stennicke, PhD, Birgitte Ursø, PhD: Novo Nordisk, Måløv, Denmark. Drs. Andersson and Sumariwalla contributed equally to this work. Drs. Tornehave, Haase, Agersø, and Stennicke own stock or stock options in Novo Nordisk. Dr. Feldmann has received consulting fees from Novo Nordisk (more than $10,000). Address correspondence to Percy F. Sumariwalla, PhD, Ken- nedy Institute of Rheumatology Division, Imperial College London, 65 Aspenlea Road, London W6 8LH, UK. E-mail: p.sumariwalla@ imperial.ac.uk. Submitted for publication May 6, 2010; accepted in revised form May 12, 2011. 2617