Hypersensitivity Type II (Cytotoxic Reaction) - Causes, Pathophysiology, Complement System

Hypersensitivity Type II also known as cytotoxic hypersensitivity reaction is where antibodies produced bind directly to antigens on the surface of a membrane and then activate the complement response. Complement response involves circulating proteins that when activated lead to an inflammatory response against a target. An example of hypersensitivity II reaction are antibodies mounted against drugs such as penicillin, hydrochlorothiazide and quinones that in rare cases can bind on to the surface of some cells subsequently activating the complement response. Antibodies can also be made that target some bacteria but accidentally cross react with human cells and then activate complement. Another good example is antibodies being formed against Rh+ RBC in a Rh - person. In order for the antibodies to be made in the first place, there must be a first contact.