# Macrophage --- **Macrophages** are [[white blood cells]] that has a role in the [[innate immune system]]. It lives in the bodys tissues, and they are differentiated by what type of tissue they live in (i.e. lung macrophages, etc). They are [[phagocytosis|phagocytes]], and can be activated by other cells under certain circumstances to release [[antimicrobial substances]] like nitric oxide. Unlike other phagocytes, macrophages have a special ability that is unique to them, called **antigen presenting**. During the [[phagocytosis#Step 5 Expulsion|expulsion phase]] of phagocytosis, instead of simply expelling all the broken down bacterial pieces like every other phagocyte, they *also* retain some bits to attach to proteins that they *then* embed into their membrane on [[MHC molecule]] as a way of keeping a record of what they have destroyed. This way [[helper T-cells]] can also come by and be activated. ![[macrophage.png]] Above: Macrophage fighting bacteria. Red blood cell for scale. If macrophages cannot destroy a bacterium, they might just wall it off to form a **granuloma** such as what we see with [[tuberculosis]]. ![[TB granuloma.png]] ## Inflammation During [[inflammation]], macrophages that live in the affected area release [[cytokines#Chemokines|chemokines]] which cause [[chemotaxis]] that can allow more [[white blood cells]] to enter into the tissue to fight the bacteria or heal the tissue damage. [[Neutrophils]] in particular respond to this [[chemotaxis]]. ## Problems with Macrophages - [[atherosclerosis|foam cells]]: If macrophages enter in to the cell wall of a damaged ___