What are Macrophages?

About Macrophages:

• Macrophages are a type of white blood cellthat plays an important role in the human immune system.
• They carry out various functions, including engulfing and digesting microorganisms, clearing out debris and dead cells, and stimulating other cells involved in immune function.
• The term macrophage is formed by the combination of the Greek terms "makro" meaning big, and "phagein" meaning eat.
• Formation:
  • Macrophages form from monocytes, which themselves derive from the bone marrow.
  • Monocytes circulate through the blood for one to three days before migrating into tissues, where they become macrophages or dendritic cells(i.e., a type of antigen presenting cell that plays a role in linking the innate and adaptive immunity).
• Macrophages can be found within many organs in the body, including the liver, brain, bones, and lungs, as well as in the blood, particularly at sites of infection.
• They are essential for the maintenance and defence of host tissues, doing so by sensing and engulfing particulate matterand, when necessary, initiating a pro-inflammatory response. 
• They can modify themselves to form different structuresin order to fight various different microbes and invaders.
• In this way, macrophages provide the first line of defense in protecting the host from infection.
• They are also involved in the development of non-specific or innate immunity.
  • This type of immunity is a long-term immunity which is acquired when a macrophage ingests a microbe and presents the microbe's antigen on its surface to alert other white blood cells to the presence of the invading particle.
  • Other white blood cells then multiply and amount an immune response against the pathogen.
• Macrophages produce a variety of cytokines, which are signaling molecules that communicate with other cells of the immune system.
• Macrophages may have different names according to where they function in the body. 
  • For example, macrophages present in the brain are termed microglia,and in the liver sinusoids, they are called Kupffer cells.