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Macrophages are food cells whose main role in the human body is to carry out phagocytosis, i.e. the absorption and destruction of, among others, microorganisms, microorganisms and damaged, abnormal or dying cells. They play a very important role in the human body's immune response (both innate and acquired), initiate and regulate the inflammatory process, destroy microorganisms, and eliminate abnormal cells (e.g. cancerous) and initiate the process of tissue regeneration.
Macrophagesare derived from monocytes, which arise from the colony-forming unit (macrophage) (CFU-M) in the red bone marrow.
In children, red bone marrow fills all bones, both long and flat. In adults, it is replaced with yellow bone marrow, and red marrow is found in flat bones, which include pelvic bones, sternum, vertebral bodies, ribs, skull bones, scapulae and epiphyses of long bones.
CFU-M cells proliferate, differentiate and mature as they go through the following stages:
- monoblasts
- promonocytes
- monocytes
After maturation is complete, monocytes leave the bone marrow and enter the circulating blood. After passing from blood through the endothelium of blood vessels to tissues, monocytes become tissue macrophages.
Stem pluripotent cell → myeloid stem cell → CFU-GM cell → CFU-M cell
→ monoblast → promonocyte → monocyte → macrophage → tissue macrophage
Macrophage activation
Activation of macrophages increases their feeding abilities, increases their cytotoxicity in relation to damaged cells of the body and increases their bactericidal properties.
Macrophages can be activated by 2 main groups of factors, both physiological (which come from the body's own body) and pathological (e.g. they are produced by microorganisms, including endotoxins produced by bacteria).
They most strongly activate cytokine macrophages, i.e. factors released mainly by stimulated mast cells (mast cells) and T lymphocytes, in particular interferon gamma (IFN-gamma).
Activated macrophages receive a signal to start phagocytosis, which consists in absorbing and destroying betweenother microorganisms or damaged cells.
Moreover, they secrete pro-inflammatory cytokines and present antigens of absorbed microorganisms on their surface.
Other cells of the immune system (helper T cells) recognize them and stimulate the production of specific antibodies against them.
Macrophages: morphological forms
The functions performed by macrophages vary and depend mainly on the type of tissue in which they are found. They can take various morphological forms:
- in the liver - Browicz-Kupffer cells, i.e. resident macrophages in the sinus vessel wall in the liver
- in the lungs - alveolar macrophages are an important component of the pulmonary defense mechanisms - their task is to phagocytose and digest bacteria and other foreign particles (e.g. dust, tobacco smoke, asbestos, silicon)
- in the epidermis - Langerhans cells
- in bone tissue - osteoclasts (i.e. bone-like cells)
- in the central nervous system - microglia
However, it is worth noting that macrophages are found not only in he althy connective tissues, but also in all organs of the human body.
Macrophages: functions
Macrophages play a key role in the human immune system, initiating antibacterial, antiparasitic, antifungal and antiviral reactions, as well as removing damaged cells and tissues, and initiating the process of repairing them.
They take part in both the specific and non-specific immune response of the organism by phagocyting and displaying antigens on their surface.
High phagocytic activity of macrophages is due to the rich set of proteolytic enzymes found in them.
It is worth noting that they are also responsible for the secretion of various factors that are to stimulate or inhibit the action of lymphocytes (including some complement factors, interferon, prostaglandins, interleukins) as well as the secretion of pro-inflammatory factors (cytokines, chemokines, enzymes, free oxygen and nitric oxide radicals) that regulate the initiation and regulation of the inflammatory process.