Model of HPC mobilization.

In this model the mobilizing stimulus (eg, G-CSF) acts directly on a mature subset of hematopoietic cells resulting in their activation; in the case of G-CSF, the likely (but unproven) target cell population is neutrophils. The mechanism by which these activated cells lead to HPC mobilization is not yet clear, but it may include the release of cytokines or extracellular matrix-degrading proteases. (See text for discussion.)