A6.21 NF-κB-inducing kinase (NIK) is expressed in synovial endothelial cells in early arthritis patients and correlates with markers of inflammation

Background and objectives The NF-κB family of transcription factors is strongly involved in synovial inflammation. We have previously shown that NF-κB-inducing kinase (NIK) is a key regulator of inflammation-induced angiogenesis in rheumatoid arthritis (RA) synovial tissue (ST). Here, we investigated synovial NIK expression in early arthritis patients and in autoantibody-positive individuals at risk for developing RA. Materials and methods ST biopsies were obtained via arthroscopy from 154 early arthritis patients (arthritis duration Results In early arthritis patients, NIK was predominantly expressed in EC of small blood vessels. Furthermore, NIK expression correlated with ESR (r = 0.184; p = 0.024), CRP (r = 0.194; p = 0.017), joint swelling (r = 0.297; p + lining and sublining macrophages r = 0.585; p + T cells r = 0.733; p + B cells r = 0.264; p = 0.040), MRI effusion (r = 0.665; p + EC were present, but this was not predictive for the development of arthritis. Conclusions NIK + EC are present in the earliest phase of synovial inflammation and may be indicative of high angiogenic activity in the inflamed ST. Therefore, NIK + EC may play an important role in the persistence of synovitis. Collectively, our data underscore the importance of angiogenesis in synovial inflammation and identify NIK as a potential therapeutic target in arthritis.