Hypersensitivity refers to an increased immune response, classified into four types: IgE-mediated (Type I), antibody-mediated (Type II), immune complex-mediated (Type III), and delayed-type hypersensitivity (Type IV). Immediate hypersensitivity occurs within 12 hours, while delayed-type hypersensitivity takes 24-48 hours, often involving T cells and cytokines. The document details the mechanisms and examples of each type, highlighting the roles of various immune cells and antibodies.

1. Hypersensitivity

2.  Definition
 Types-
 1. IgE- mediated hypersensitivity (type I)
 2. Antibody- mediated hypersensitivity (type II)
 3. Immune complex- mediated hypersensitivity (type
III)
 4. Delayed-type hypersensitivity (type IV)

3.  Increase immune response is termed as hypersensitivity
or allergy.
 When immune system work fast then it is required.
 Types-
 1. immediate hypersensitivity
 2. delayed-type hypersensitivity (DTH)

4. Immediate
hypersensitivity
Delay-type
hypersensitivity
Its response is very early, with
in 12 hours of antigen attacks.
Its response in little slow, it
takes 24-48 hours.
By antigen-antibody complex
or by reactive antibody forms.
By reactive TH cell, antigen
presenting cell present antigen
to TH cell

5.  1. IgE mediated (type-I) hypersensitivity
 2. Antibody-mediated (type-II)
hypersensitivity
 3. Immune complex-mediated (type-III)
hypersensitivity
 4. Delayed-type hypersensitivity (DTH)

6.  IgE- mediated hypersensitivity
 Most common cell involved in type-I are basophills
and mast cells, because IgE receptor present on the
surface of basophills and mast cells
 Antigen act as allergence generate allergy
 Ex: asthma

8.  Antibody-mediated hypersensitivity
 IgG & IgE
 Compliment protein play important
role in type-II
 Compliment immediated destruction.
 ADCC (NKC) response because due
to the receptor of IgE & complex
protein present on the surface of
antigen.
 Ex: auto immune hemolytic cell
Erythroblastosis fetalis

10.  Immune complex-mediated hypersensitivity.
 The reaction of antibody with antigen generates
immune complexes.
 Large amounts of immune complexes can lead to
tissue-damaging type III hypersensitivity reactions.

12.  Delayed-type hypersensitivity
 When some subpopulations of activated TH cells
encounter certain types antigens, they secrete cytokines
that induce a localized inflammatory reaction.
 Generally the T cells activated during the sensitization
phase are CD4+, primarily of the TH1 subtype.
 But in a few cases CD8+ cells have also been shown to
induce a DTH response.