High-mobility group box protein 1 (HMGB1) expression in collagen-induced arthritis. The presence of cells expressing HMGB1 in the invading pannus of collagen-induced arthritis is shown. In this experiment, the section was stained for HMGB1 using affinity-purified polyclonal rabbit anti-HMGB1 antibodies (BD Pharmingen, San Diego, CA, USA) followed by biotin-labeled Fab2 fragments of a donkey anti-rabbit antibody (Jackson ImmunoResearch Laboratories, Inc., West Grove, PA, USA). The sections then were exposed to avidin-biotin-horseradish peroxidase (Vectastain Elite, ABC kit; Vector Laboratories, Burlingame, CA, USA), and color reaction was generated with diaminobenzidine (DAB). Reproduced with permission from Nature Insight 2002, 420: 845–846 http://www.nature.com/nature/insights/6917.html. Copyright 2002, Macmillan Publishers Ltd.