Factors masking HMGB1 in human serum and plasma

Abstract: High mobility group box 1 protein (HMGB1) is a ubiquitously expressed architectural chromosomal protein. Recently, it has become ob-vious that HMGB1 can also act as a proinflamma-tory mediator when actively secreted during cell activation or passively released from necrotic cells. HMGB1 appears to play an important role in the pathogenesis of diseases, including sepsis and rheu-matoid arthritis. However, easy, sensitive, and re-liable detection systems are required to investigate the clinical significance of HMGB1 in clinical sam-ples for diagnosis and prognosis of diseases. Here, we describe sensitive ELISAs for the detection of HMGB1 in cell culture medium and cell lysates. However, these assays failed to reliably quantitate HMGB1 in serum and plasma when compared with immunoblot analysis. We found that serum/plasma components bind to HMGB1 and interfere with its detection by ELISA systems. In most serum/plasma samples investigated, including those from healthy individuals, we detected IgG antibodies binding to HMGB1. The titers of these antibodies correlated with the capacity of sera to interfere with the de-tection of recombinant HMGB1 by ELISA. Fur-thermore, HMGB1 coimmunoprecipitated with several proteins including IgG1, as identified by mass spectrometry. These HMGB1 interacting proteins are currently characterized and may con-tribute to complex formation, masking, and possi-bly, modulation of cytokine activity of HMGB1. J