Type II hypersensitivity

Having a hypersensitivity means that the immune system is reacting to something in a way that damages the body rather than protecting it.

There are four different types of hypersensitivities, and the second type or type II hypersensitivity is sometimes called cytotoxic hypersensitivity because a lot of disorders caused by this hypersensitivity involve antibody mediated destruction of healthy cells.

These disorders tend to be tissue specific meaning that the antibodies are generally specific to one type of tissue or organ.

There are other antibody-mediated hypersensitivities that are systemic, and these are generally Type III hypersensitivities.

Our immune system is setup to fight anything that is considered “non-self” right? Anything that’s not “self”, or you.

This works in large part because of a process called central tolerance which is when developing immune cells that are self-reactive get destroyed or inactivated, whereas immune cells that aren’t are allowed to survive.

This happens while they are still in their primary lymphoid organs, which is the thymus for T cells and the bone marrow for B cells.

This process, though, is not perfect and some self-reactive B and T cells will escape.

These escaped self-reactive cells can then attack healthy tissue and result in autoimmune disease.

In type II hypersensitivity these escaped self-reactive B cells become activated and produce IgM or, with the help of CD4 positive T helper cells, IgG antibodies that attach to antigens on host cells.

There are two type of antigens involved with type II hypersensitivity: intrinsic meaning an antigen the host cell normally makes or extrinsic which is an antigen from an infection or even some medications, like penicillin that gets attached to the host cell.

Alright so let’s say a drug, like penicillin, binds to a red blood cell - well it becomes an extrinsic antigen.

An IgG or more rarely an IgM antibody that is penicillin specific might bind to the penicillin molecule, creating an antigen-antibody complex.