Myelin phagocytosis by macrophages and nonmacrophages during Wallerian degeneration.

The literature concerning Schwann cells (SCs) and macrophages in myelin phagocytosis during Wallerian degeneration is reviewed. SCs carry out the first step in the removal of myelin by segmenting myelin and then incorporating the degraded myelin. The recruited macrophages then join in the myelin-phagocytosis event, appearing to make full use of their original phagocyte abilities until the end of myelin clearance. The molecular mechanisms of the two cells underlying myelin phagocytosis are thought to be different; myelin phagocytosis by SCs being lectin-mediated, i.e., opsonin-independent, whereas that of macrophages is mainly opsonin-dependent. It is important to note that SCs and macrophages cooperatively accomplish myelin phagocytosis.