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.
So hypersensitivity is an exaggerated or
inappropriate immune response leading to pathology.
I think it’s quite important to
understand that all of the responses
you will be looking at are actually normal immune responses.
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.
We can classify hypersensitivity reactions
into one of four different types.
Type I is IgE-mediated
mast cell degranulation.
Type II is cytotoxic antibodies
against cell surface antigens.
Type III is immune complex
And Type IV is delayed type
hypersensitivity mediated by T-cells.
So note that types I, II and III were all mediated
by antibody whereas Type IV is mediated by T-cells.