Identification, characterization, and physiological actions of factor H as an adrenomedullin binding protein present in human plasma

A recently discovered adrenomedullin binding protein has been characterized as complement factor H, an important regulator of the complement cascade. This review will describe the evidence that led to the identification of factor H as an adrenomedullin binding protein and will address the implications that such binding has in the radioimmunoassay of AM in plasma. We will also describe the possible physiological implications of AM binding: namely, factor H suppresses the antimicrobial activity of AM, enhances AM-mediated induction of cyclic-AMP in rat fibroblasts, and augments the AM-mediated growth of a human cancer cell line. These initial studies suggest that factor H may be an important factor in the regulation of AM physiology. The elucidation of the mechanisms that modulate AM activity will be necessary for the understanding of the role of AM in normal and pathological conditions.