This document discusses immunity and hypersensitivity reactions. It defines immunity as the body's ability to prevent infection from pathogens like bacteria and viruses. There are two types of immunity: innate immunity which is present at birth, and acquired immunity which develops after exposure to an antigen. Hypersensitivity refers to excessive immune responses that can damage the body's own tissues. There are four types of hypersensitivity reactions - Type I is an immediate reaction mediated by IgE, Type II involves cytotoxic reactions, Type III involves immune complexes, and Type IV is a delayed cell-mediated response that peaks 48 hours after antigen exposure.

1. Bsc nursing 1 year
Microbiology
Unit :- 5 (immunity)
BY:- PRAGYA TIWARI

2. Immunity :-
 Immunity refers to the body’s ability to prevent the invasion of pathogens.
Pathogens are foreign disease-causing substances, such as bacteria and viruses,
and people are exposed to them every day.Antigens are attached to the surface
of pathogens and stimulate an immune response in the body. An immune
response is the body’s defense system to fight against antigens and protect the
body.
 The types of diseases that are prevented by vaccines are called “vaccine-
preventable diseases.” Examples of these diseases include chickenpox (varicella)

3. Types of immunity :-

4. Types of immunity :-
 Innate immunity is general protection that a person is born with, including
physical barriers (skin, body hair), defense mechanisms (saliva, gastric acid), and
general immune responses (inflammation).
 Acquired (adaptive) immunity is a type of immunity that develops from
immunological memory. The body is exposed to a specific antigen (which is
attached to a pathogen) and develops antibodies to that specific antigen . The
next time same antigen invades, the body has a memory of the specific antigen
and already has antibodies to fight it off. Acquired immunity can occur from
exposure to an infection, wherein a person gets a disease and develops
immunity as a result. Acquired immunity also occurs from vaccination

6. Hypersensitivity :-
 Hypersensitivity refers to excessive, undesirable (damaging, discomfort-
producing and sometimes fatal) reactions produced by the normal immune
system. Hypersensitivity reactions require a pre-sensitized (immune) state of the
host.
 Hypersensitivity is an immune response that damages the body’s own tissues.

7. Types of hypersensitivity reaction :-
They are mainly 4 types :-
1. Hypersensitivity type I
2. Hypersensitivity type II
3. Hypersensitivity type III
4. Hypersensitivity type IV

8. Type I hypersensitivity :-
Type I hypersensitivity is also known as immediate or anaphylactic hypersensitivity.
The reaction may involve skin (urticaria and eczema), eyes (conjunctivitis),
nasopharynx (rhinorrhea, rhinitis), bronchopulmonary tissues (asthma) and
gastrointestinal tract (gastroenteritis).
The reaction may cause a range of symptoms from minor inconvenience to death.
The reaction usually takes 15 – 30 minutes from the time of exposure to the antigen,
although sometimes it may have a delayed onset (10 – 12 hours).
Immediate hypersensitivity is mediated by IgE.

9. Type II hypersensitivity :-
Type II hypersensitivity is also known as cytotoxic hypersensitivity and may affect a
variety of organs and tissues.
The antigens are normally endogenous, although exogenous chemicals (haptens)
which can attach to cell membranes can also lead to type II hypersensitivity. Drug-
induced hemolytic anemia.

10. Type III hypersensitivity :-
Type III hypersensitivity is also known as immune complex hypersensitivity. The
reaction may be general (e.g., serum sickness) or may involve individual organs
including skin The reaction may take 3 – 10 hours after exposure to the antigen (as
in Arthus reaction). They are mostly of the IgG class, although IgM may also be
involved.

11. Type IV hypersensitivity:-
Type IV hypersensitivity is also known as cell mediated or delayed type
hypersensitivity. The classical example of this hypersensitivity is tuberculin (Montoux)
reaction (figure 5) which peaks 48 hours after the injection of antigen (PPD or old
tuberculin).