Integrin alpha2beta1, which is a membrane protein consisting of noncovalently bound alpha2 and beta1 chains, mediates cell binding to collagen and plays a role in platelet functions. DNAs encoding the chimeric proteins in which the extracellular domains of each alpha2 and beta1 chain was fused to hinge and Fe regions of human IgG(1)gamma chain were cotransfected into CHO cells. Soluble integrin alpha2beta1 (salpha2beta1) in which alpha2 and beta1 chains were covalently bound by disulfide bonds was recovered from the culture supernatant. salpha2beta1 maintained functional characteristics of cell surface alpha2beta1 as indicated by cation-dependent binding to collagen and conformational changes induced by cations or ligand. Intravenously administered salpha2beta1 in rats colocalized with collagen in inflamed microvessels. Moreover, salpha2beta1-conjugated liposome administered intravenously reduced bleeding time of the thrombocytopenic mice. These results indicated that salpha2beta1 has pharmaceutical utilities as an agent for detecting injured vessels and a component of platelet substitute. (C) 2002 Elsevier Science.