This week’s word is macrophage.
mac·ro·phage ˈmakrəˌfāj/ noun (from Greek makros “large” and phagein “eat”) a cell with one nucleus (mononuclear), made in the bone marrow and released into the bloodstream as a monocyte. Once it moves into the tissues, it becomes a macrophage. When stimulated by inflammation, infection, and chemicals produced by the immune system, macrophages gobble up (phagocytize) foreign particles and infectious agents.
Macrophages play a hugely important role in a functioning immune system in all animals. They are fairly large cells, and they are the little garbage trucks in our bodies. They remove dying or dead cells, debris, and pathogens by engulfing them, then using a cell structure called a lysosome to digest the cell or particle. Macrophages are smart: after digesting a pathogen, they tell other white blood cells in the body (specifically helper T cells) that they’ve captured an enemy. This allows the immune system to mount other defenses, such as producing antibodies and releasing chemicals that attract more macrophages to do battle.
Macrophages are stationed in various places in the body, such as the lungs, intestines, liver, kidneys, lymph nodes, and skin, as sentinels against invasion. They play a role in muscle regeneration, healing of wounds, recycling iron from red blood cells, and regeneration of limbs (think salamander).
Macrophage turned killer?
Sometimes, pathogens use macrophages to their own advantage. One distinct example in our domestic cats is the disease known as Feline Infectious Peritonitis (FIP). This is a complicated, devastating disease in cats, that is uniformly fatal and for which we have no treatment. It’s caused by a virus, called the Feline Enteric Coronavirus (FEC). Most cats infected with FEC do not develop serious illness and recover with no lasting effects. However, in some cats, the virus mutates and becomes a killer by hijacking macrophages. The macrophages that eat up the mutated virus unwittingly spread it throughout the body. Cats with FIP may present with the “wet” form (thick yellow fluid accumulates in the abdomen and/or chest) or the “dry” form (inflammation of the eyes and nervous system). Both forms cause fever that doesn’t respond to treatment and poor appetite.