M1 or classically activated macrophages play a key role in the immune response to foreign pathogens such as bacteria, which can cause immeasurable damage to the host. M1 macrophages also have an enhanced ability to produce nitric oxide, present antigens, and secrete large numbers of chemokines. 

M2 or alternatively-activated macrophages play a key role in tissue repair, wound healing, and limiting inflammation. They also express copious quantities of extracellular matrix-related proteins and cytosolic arginase.