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My name is Herman Waldmann from the Department of Pathology in Oxford,
the Dunn School of Pathology,
and I'm going to give you a lecture on hypersensitivity diseases.
What are the hypersensitivity diseases?
These are adaptive immune responses to an antigen that instead of doing good,
result in damage to the host tissues.
You can think of them as an exaggeration of normal immune mechanisms,
and the antigens concerned can be either foreign antigens or indeed self-antigens.
When they're self-antigens, we think of them as autoimmune diseases.
Classically, the hypersensitivity diseases have been
classified by Gell and Coombs into four categories.
The first, type I, is caused by IgE,
one of the immunoglobulin classes,
and gives what's called immediate hypersensitivity.
That will be the topic of my lecture.
Type II hypersensitivity occurs when antibodies are targeted to cells,
and then cause them damage.
Really, there are variants of type II where the antibody
act as an agonist and binds to a receptor and stimulates that receptor.
For example, in hyperthyroidism in Graves disease,
this can be thought of as a type II or some people have referred to it as a type V.
In general, type II diseases are due to antibody binding,
either fixing complement, or attracting phagocytic cells with Fc receptor.
Type III hypersensitivity diseases are due to
antibody-antigen complexes that circulate and then deposit in tissues.
Finally, type IV hypersensitivity diseases are not caused by antibody
but caused by T cells that can target their antigen wherever it's located.
I'm going to focus on type I.