Kinetics of inhibition of CFU-C homing in long-term marrow culture.

We have previously shown that galactosyl- and mannosyl-BSA inhibit the binding of hemopoietic progenitor cells to their supporting stroma (homing) in long-term marrow culture, suggesting that the homing is mediated by a molecular recognition with galactosyl and mannosyl specificities. In the present work we studied the kinetics of this inhibition. In the absence of inhibiting reagents, total cell and CFU-C production continued linearly as a function of time in culture. When inhibiting reagents were incorporated at the time of initiation of cultures, cell and CFU-C production was halted, suggesting that the binding of progenitor cells to stroma was necessary for subsequent cell proliferation and differentiation. When inhibiting reagents were introduced 1 week after the initiation of culture, cell and CFU-C production continued at a much lower rate than that of control, suggesting that although the inhibiting reagents can inhibit the binding of progenitor cells to stroma, they are less effective in displacing those already bound. Finally, when the inhibiting reagents were removed from the cultures, cell and CFU-C production resumed at a rate similar to that of controls, indicating that these reagents do not alter the integrity of progenitor cell or stroma.