 Macrophages also play a role in inducing the proliferation of Schwann cells that occurs during Wallerian degeneration.Supernatant has been collected from medium in which macrophages are active in myelin phagocytosis where lysosomal processing of the myelin occurs within the macrophage.The supernatant contains a mitogenic factor, a mitosis promoting factor, that is characterized heat and trypsin sensitivity, both of which characterize it as a peptide.