HMGB1 and rheumatoid arthritis: Based on the expectation that HMGB1-treated RA fibroblasts produce high levels of angiogenic factors, we compared HMVEC tube formation after treating them with conditioned medium (CM) derived from HMGB1 (100 ng/ml, for 48 hr)-stimulated RA fibroblasts or CM from vehicle-treated fibroblasts.