Phagocyte notes - Unit 1

Simple notes on Phagocytes.

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Phagocytes are the white blood cells that protect the body by ingesting
(phagocytosing) harmful foreign particles, bacteria, and dead or dying cells. They are
essential for fighting infections and for subsequent immunity. One litre of human
blood contains about six billion phagocytes. Phagocytes were first discovered in 1882
by Ilya Ilyich Mechnikov while he was studying starfish larvae. Mechnikov was awarded
the 1908 Nobel Prize in Physiology or Medicine for his discovery. Phagocytes occur in
many species; some amoebae behave like macrophage phagocytes, which suggests
that phagocytes appeared early in the evolution of life.
Phagocytes of humans and other animals are called "professional" or
"non-professional" depending on how effective they are atphagocytosis. The
professional phagocytes include cells
called neutrophils, monocytes, macrophages, dendritic cells, and mast cells. The main
difference between professional and non-professional phagocytes is that the
professional phagocytes have molecules called receptors on their surfaces that can
detect harmful objects, such as bacteria, that are not normally found in the
body. Phagocytes are crucial in fighting infections, as well as in maintaining healthy
tissues by removing dead and dying cells that have reached the end of their lifespan.
During an infection, chemical signals attract phagocytes to places where the
pathogen has invaded the body. These chemicals may come from bacteria or from
other phagocytes already present. The phagocytes move by a method
called chemotaxis. When phagocytes come into contact with bacteria, the receptors
on the phagocyte's surface will bind to them. This binding will lead to the engulfing of
the bacteria by the phagocyte. Some phagocytes kill the ingested pathogen
with oxidants and nitric oxide. After phagocytosis, macrophages and dendritic cells
can also participate in antigen presentation, a process in which a phagocyte moves
parts of the ingested material back to its surface. This material is then displayed to
other cells of the immune system. Some phagocytes then travel to the body's lymph
nodes and display the material to white blood cells called lymphocytes. This process
is important in building immunity. However, many pathogens have evolved methods
to evade attacks by phagocytes.


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