Quantitation of spreading factor in human biologic fluids

Spreading factor (SF) is a glycoprotein isolated from human plasma or serum that promotes attachment and spreading of a wide variety of mammalian cells in culture. Under appropriate conditions, this factor also affects cell proliferation and differentiation in vitro. An immunoassay employing a previously characterized monoclonal antibody to SF, with purified SF as a reference standard, was utilized to quantitate levels of SF in human plasma, serum, amniotic fluid, and urinary protein. Specific anti-SF monoclonal antibody-binding activities in individual samples of human serum were identical to specific anti-SF monoclonal antibody-binding activities in the plasma samples from which the sera were derived. Specific anti-SF monoclonal antibody-binding activity in plasma from adults, when compared with purified SF reference standards, represented an average of 4 micrograms of SF per mg plasma protein (range, 2.5 to 7 micrograms/mg). Specific anti-SF monoclonal antibody-binding activity in sera from fetal cord blood, infants, children, or adolescents was not significantly different from that of adults. Specific anti-SF monoclonal antibody-binding activities in amniotic fluid samples from pregnancies of 12 to 23 weeks' gestation were within the range observed in sera of adults. Anti-SF monoclonal antibody-binding activity in concentrated urinary protein, when compared with purified SF reference standards, represented a specific activity of 10.9 micrograms of SF per mg protein.