These cells are found in one form or another in nearly all body tissues. There are several specialized members of this cell type family which are specific to a particular body compartment or organ. As such they are often described with a special name, for example, Kupfer cells are an example of a specialized liver macrophage.

Phagocytosis

All macrophages are phagocytic cells that represent the first line of innate defense against invading pathogens. As well as playing their part role in innate immunity, macrophages also internalize damaged body cells, oncogenic cells, and general extracellular debris for processing and clearance, promoting wound healing and helping to maintain overall body health and vitality. This phagocytic process can also be initiated by actication of hte complement signaling system.

Antigen presentation

Once a phagocytosed pathogen has been internalized and digested, its antigens are presented on the macrophage's cell surface. If a naive T cell match and binds to the antigen presented by the macrophage it will begin to proliferate, producing many daughter T helper cells (TH1 cells) with identical receptor specificity.

Induction of inflammation

Macrophages play an important role in creating an inflammatory condition to promote pathogen clearance and would healing. The cells achieve this by manufacturing and secreting a range of chemotactic ('cell recruiting') and vasodilatory ('blood vessel dilating/leak making) factors. On secretion of the molecules the 4 classical signs of inflammation will be achieved;

  • pain, due to simulation of nociceptive neurones

  • swelling, due to the local accumulation of immune cells

  • heat, brought from the core as a result of fluid leaking from capillaries to extravascular tissues

  • redness, due to the dilation and enlargement of capillaries just inder the skin's surface.