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autoantibody p. 113
polymyositis/dermatomyositis p. 483
B- lymphocytes produce antibodies against a specific part of these foreign pathogens, called antigen.
The tips of these antibodies strongly binds to this antigen, while the base of the antibody, called the constant region, gets recognized by complement proteins.
These complement proteins are a group of small proteins made by the liver that work together.
One complement protein cuts or cleaves the next one, activating it and creating an enzymatic cascade.
C1 then cleaves C2 and C4.
Portions of the C2 and C4 binds to the antigen and form an enzymatic complex that cleaves C3 into two portions, C3a and C3b.
C3b joins the enzymatic complex and then the complex is able to cleave C5 into two portions, C5a and C5b portion.
C5a and C3a float off into the blood where they attract other cells of the immune system to the affected area.
Meanwhile, C5b, C6, C7, C8 and multiple C9 proteins, come together on the surface of the pathogen to form the membrane attack complex or MAC.
The MAC attacks pathogenic cells, such as bacteria, by creating a channel in the cell membrane.
Because cells have more solutes in them than the outside environment, water flows into the cell by the process of osmosis, and that causes the cell to swell up and burst, which is called cell lysis.
In dermatomyositis, immune cells confuse normal muscle and skin proteins with foreign antigens.
This process is called molecular mimicry because from the perspective of the immune cells, a host protein is mimicking a foreign or tumor protein.
Dermatomyositis (DM) is a rare autoimmune disease that leads to inflammation and damage of the muscles and skin. It is associated with complement system activation, and autoantibodies like ANA, anti-Mi-2 and, anti-Jo-1 which result in proximal muscle weakness and photosensitive skin rashes. DM presents with muscle weakness, which often becomes worse over time, as well as a distinctive skin rash.
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