The macrophage is a type of white blood cell that aids in the elimination of foreign substances by ingesting them and activating an immunological response.

Macrophages are components of the reticuloendothelial system (or mononuclear phagocyte system) and are found in nearly all bodily tissues.

In certain circumstances, macrophages are immobile within tissues, such as in lymph nodes and the intestines.

In other instances, they may roam the crevices between connective tissues. As a collective, they can consume other cells, pathogenic agents, and several other minute particles, such as specific colours and colloids.

By consuming and processing foreign particles, macrophages serve a crucial role in allowing lymphocytes, which determine the specificity of the immune response, to recognise them.

Monocytes in the bone marrow differentiate into macrophages.

The granulocyte-macrophage colony-stimulating factor stimulates the development of precursor cells into monocytes. After leaving the bone marrow, they circulate in the circulation.

Hours later, the monocytes penetrate the tissues, where they transform into macrophages.

In different organs, specialised macrophages are known by different names; for example, those in the liver are known as Kupffer cells, whilst those in the skin are known as Langerhans cells.