Phagocytes
Phagocytes include monocytes and macrophages. Monocytes morph into macrophages upon leaving the circulatory system to attend to tissue damage or infection.
Phagocytes are significant throughout the animal kingdom, and quite evolved in vertebrates. A liter of human blood has about 6 billion phagocytes.
Vertebrates with jaws have 2 types of phagocyte: “professional” and “non-professional,” a distinction made by their effectiveness at phagocytosis.
Monocytes, macrophages, neutrophils, mast cells, and dendritic cells are the pros. Professional phagocytes possess surface receptors to detect pathogens, and some have the means to kill infected cells.
Phagocytic receptors involve opsonins: molecules that tag an antigen for immune response. This includes antibodies and complement.
Phagocytosis is not the principal job of the non-professionals. Most non-pro phagocytes lack pathogen receptor detectors and the oxygen guns that the pros use.
Non-professional phagocytes include epithelium, endothelium, mesenchyme, and fibroblasts. Epithelium are the cells lining the surfaces and cavities of body structures. The skin, aka epidermis, is an epithelium. Endothelial cells line the inner surface of blood vessels. Mesenchyme comprises connective tissues, such as cartilage and bone. Fibroblast cells work in wound healing.
