Polarization is a categorization scheme for the cell state and behavior of the immune cells known as macrophages, which play a variety of roles in the body, ranging from the destruction of invaders and errant cells to assisting in regeneration. For the purposes of this discussion, the interesting states are M1, inflammatory and aggressive towards intruding pathogens, and M2, in which macrophages suppress inflammation and undertake other activities that aid in regeneration. Both have their roles to play, but many of the issues that arise in aged individuals are made worse by the increasing tendency of macrophages to exhibit the M1 polarization, even when it is unhelpful to do so.
While transient inflammation is a necessary part of the immune response, chronic inflammation (such as that produced by excess fat tissue or aging) is known to be disruptive to tissue maintenance and regeneration. This consideration of macrophages and inflammation is a thin slice of a much more complicated picture, but it is an important slice. While it is true that many other changes also take place in the aged immune system, here at least, researchers appear to have identified a regulatory protein that produces many of the problems exhibited by macrophages
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