Cloning, distribution and primary immune characteristics of amphioxus alpha-2 macroglobulin.

Alpha-2 macroglobulin (α(2)M), a broad-spectrum protease inhibitor, exists widely in vertebrates and invertebrates, but little information is available to date regarding α(2)M in amphioxus, an animal bridging from invertebrates to vertebrates. Here we first show that the full α(2)M cDNA of Branchiostoma japonicum (Bjα(2)m) contained 5545 bp with an open reading frame of 4593 bp encoding signal sequence of 16 amino acid residues and a mature protein of 1514 residues. The calculated molecular mass and pI of mature Bjα(2)M were 164.2 kDa and 4.6 respectively. Bjα(2)m was mainly expressed in the hepatic caecum and hind-gut in a tissue-specific manner, contrasting to the primary expression of α(2)M in vertebrate liver. Following challenge with lipopolysaccharide (LPS), Bjα(2)m expression was significantly up-regulated (7-folds) at 8 h and then declined to the base line at 16 h. Taken together, it is suggested that Bjα(2)M is an immune-relevant molecule possibly involved in the acute phase response via the digestive organs.