During initial differentiation of macrophages from monocytes, macrophages can differentiate into either M1 macrophages or M2 macrophages. M1 macrophages are considered kill-type macrophages. In the course of an infection, these are the macrophages which will kill the foreign intruder and sterilize the wound. M1 macrophages accomplish this task by metabolizing arginine to nitric oxide, which is cytotoxic to invading cells. M2 macrophages are considered repair-type macrophages. In the course of an infection, these are the macrophages that will promote new growth of the surrounding tissue to repair the damage of the infection. M2 macrophages accomplish this task by metabolizing arginine to ornithine, which is critical in the regulation of cell proliferation.
Tuning Macrophages for Immunotherapy
The term macrophage comes from the Greek words makros, meaning large, and phagein, meaning to eat. Macrophages patrol the body seeking any cell types that do not display the proper protein surface markers and consume these foreign intruders in a process called phagocytosis. This process is useful for removing a variety of foreign substances, including potentially cancerous cells. However, cancerous cells are able to exploit the body’s immune system to prevent destruction by macrophages and possibly encourage proliferation of the cancerous cells.