Question

Why are type IV hypersensitivities different from the other three types.

Answer 1

Answer :- To know the answer of this question first we need to know what is hypersensitivity.

Hypersensitivity is an exaggerated immune response that results in tissue damage and is manifested in the individual on a second or subsequent contact with an antigen.

Hypersensitivity is classified into 4 types i.e

Type-I , Type-II , Type-III and Type-IV.

Here Type-IV hypersensitivity is different from other 3 because Type-IV hypersensitivity is the only class of hypersensitive reactions which are triggered by antigen specific T-cells ( cell mediated immunity reactions). This is mediated by T-cell dependent effector mechanism involving TH cells, primarily of the TH1 subtype but in few cases Tc cells. So antibodies don't play a role in type IV hypersensitivity reactions.

On the other hand other three type of hypersensitive reactions are driven or causes by antibodies e.g. Type-I hypersensitive reactions are driven by IgE antibody , Type-II hypersensitive reactions are driven by IgM and IgG antibodies and Type-III hypersensitive reactions are driven by IgG antibody.

So from the above discussion we can conclude that the difference between Type-IV hypersensitivity and other 3 types of hypersensitivity is in the driving mechanism where as Type-IV is cell mediated immune reaction and other 3 are antibody mediated immune reaction.