Two decades ago, the mannosebinding lectin (MBL), or "lectin activation pathway," was discovered. Kawasaki et al. (6) found the MBL protein in 1978, but its function remained unclear until 1989, when Super et al. (7) recognized that reduced serum levels of MBL correlated with an opsonic defect in children. Matsushita et al. then detected the proteolytic activity of the MBLassociated serine proteases (MASP-1 and MASP-2), leading to the formation of the classical C3 convertase (8) (9) (10) (11) .