Question

Type II Hypersensitivity and how it connects to Pathophysiology and why is it relevant?

Answer 1

Type 2 hypersensitivity is an antibody meadiated reaction in which antibodies like IgG and IgM antibodies attach with the antigens. When immune system work abnormally it produce hypersensitivity. Type 2 hypersensitivity reaction is cytotoxic they act on specefic organ tissues in the body and cause destruction of the cells in these tissues.

Pathophysiology

Binding of antibody   with the host tissue produce following nechanism in the body

complement activation ,

antibody dependent cell mediated cytotoxicity,

antibody mediated cellular dysfunction.

IgM or IgG antibodies bind to antigen on the surface of specefic tissues . These antibodies activate the complement cascade which directly damage the host cell leads to the lysis( by making membrane attack complex) or phagocytosis ( opsonization)of the cell.

Once the antibody binds with the antigen,Fc region of the antibody produce macrophages and neutrophils which helps in phagocytosis of the cell with the help of natural killer cells

Binding of antibody to antigen or protein affects its normal function. If this antigen have any specefic functions antbody alters it and changes the normal cell function causing destruction of cell

Examples : blood tranfusion reaction ,erythroblastosis fetalis ,auto immune hemolytic anaemia ,rheumatic fever ,graves disease,good pastures syndrom, mystenia gravis etc

In good pastures syndrom antibodies produce nephritis . In mythenia gravis antibodies reduce acetyl choline.

Type 2 hypersensitivity antigens may be self one or may be from outside. It is helps the body to fight against the foreign antigen (mainly from exposed pathogens) that enter into the body through lysis or phagocytosis of the cell.