Introduction to Hypersensitivity

00:01 Hypersensitivity - this is a term that is used to describe immune responses that are inappropriate, either because they are of too great a magnitude or they’re a response to something that we really do not need the immune system to respond to, or they’re occurring at a location in the body where we shouldn’t be getting that type of immune response.

00:26 So hypersensitivity is an exaggerated or inappropriate immune response leading to pathology.

00:34 I think it’s quite important to understand that all of the responses you will be looking at are actually normal immune responses.

00:42 The problem is, they’re being directed towards something that isn’t going to cause you any harm whatsoever, or they’re taking place in a location in the body which it’s not necessary for that type of response to be occurring in, or they’re very exaggerated.

00:57 We can classify hypersensitivity reactions into one of four different types.

01:03 Type I is IgE-mediated mast cell degranulation.

01:10 Type II is cytotoxic antibodies against cell surface antigens.

01:18 Type III is immune complex mediated hypersensitivity.

01:25 And Type IV is delayed type hypersensitivity mediated by T-cells.

01:31 So note that types I, II and III were all mediated by antibody whereas Type IV is mediated by T-cells.