UNIT-4 IMMUNITY, types of immunity, innate immunity, acquired immunity, active immunity, passive immunity, natural active immunity, natural passive immunity, artificial active immunity, artificial passive immunity, use of passive immunization, immunization schedule, vaccines, hypersensitivity reactions, types of hypersensitivity reactions, types of antigens, combines immunization, local immunity, herd immunity, adoptive immunity, immunoprophylaxis, autoimmunity, serological tests.

2.  Definition
 The term ‘immunity’ is defined as resistance exhibited by
the host against any foreign antigen including
microorganisms. This resistance plays a major role in
prevention of infectious diseases.
 Immunity refers to resistance of a host to pathogens and
their toxic products.

4.  Definition
 It is the resistance which individual possess by birth. It is by
virtue of which of his genetic & constitutional make-up. It
does not depend on prior contact with foreign antigen.
 The innate immunity is the body’s first line of defense against
germs entering the body. It responds in the same way to all
germs and foreign substances, which is why it is sometimes
referred to as the nonspecific immune system.

5.  Innate Immunity can be further divided into-
1. Species Immunity- it is the total or relative resistance to a
pathogen shown by all the members of a species. For example, all
human beings are resistant to plant pathogens & many animal
pathogens.
2. Racial Immunity- Natural Immunity shared by all members of a
particular race. Example, In the USA Negroes are more susceptible to
tuberculosis than whites.
3.Individual Immunity- different individuals differ in their
resistance to microbial infections.

6.  Mechanisms of Innate Immunity
1. Epithelial Surfaces
• Skin
• Respiratory Tract
• Intestinal Tract
• Conjunctiva
• The Genitourinary Tract
2. Antibacterial Substances- there are number of nonspecific
antibacterial substances present in blood & tissues. These
substances are properdin, complement, lysozyme.

7. 3. Cellular Factors- when the infective agent crossed the
barrier of epithelial surfaces, the tissue factors come into
play for defense.
◦ An exudative inflammatory reaction occurs by accumulation of
phagocytes at the site of infection.
◦ Phagocytic cells ingest these organisms & destroy them.
◦ Some bacteria (M. tuberculosis, M. leprae) resist this type of
killing & can multiply within phagocytes & thus produce this
disease.

8.  Factors influencing Innate Immunity
 Age- very young & very old are more susceptible to infectious
diseases. This appears to be due to the immaturity of immune
system in very young & gradual decrease in the immunity ofvery
old.
 Hormonal Influence & Sex- there is an increase susceptibility to
infection in endocrine disorders such as diabetes mellitus,
hypothyroidism & adrenal dysfunction. Pregnant women are more
susceptible to microbial infections due to increased steroid levels
during pregnancy.
 Nutritional Factors- both antibody mediated & cell-mediated
immunity are lowered in malnutrition.

9.  Definition
• The resistance that an individual acquires during his
life time is known as acquired immunity. It is antigen-
specific & may be antibody-mediated or cell mediated.
• A type of immunity that develops when a person's
immune system responds to a foreign substance or
microorganism, or that occurs after a person receives
antibodies from another source.

10. ACTIVE IMMUNITY
PASSIVE IMMUNITY

11.  This involves the active involvement of person’s own
immune system leading to the synthesis of antibodies and
the production of immunocompetent cells (ICCs).
 It appears only after a lag (latent) period i.e. the time for
generation of antibodies & ICCs.

12.  Types of Active Immunity-
Natural Active
Immunity
Artificial Active
Immunity

13.  NATURAL ACTIVE IMMUNITY
oIt is acquired by clinical or subclinical infection. Such
immunity is long lasting.
oPersons recovering from small pox infection develop
natural active immunity.

14.  ARTIFICIALACTIVE IMMUNITY
oIt is produced by vaccination. The vaccines are prepared
from live attenuated or killed microorganisms or their
antigens or toxoids.
o In killed vaccines the organisms are killed by heat,
formalin, phenol & alcohol.
oToxoids are prepared from bacterial exotoxins inactivated
by formalin (formol) or alum (alum precipated toxoid-
APT).
oToxoids are immunogenic but not toxigenic.

15.  Active Immune response stimulates both humoral & cell
mediated immunity usually in parallel.
I. Humoral Immunity- it is antibody mediated immunity. It
depends on the synthesis of antibodies by plasma cells.
These cells produce specific circulating antibody which
combines specifically with the antigens & modify their
activity.
II. Cell Mediated Immunity- it depends on T-lymphocytes
developed against certain antigens. The cell mediated
immunity by sensitised T-lymphocytes is important in
resistance to chronic bacterial infections.

16.  The immunity that is transferred to a recipient in a ready-
made form is known as passive immunity.
 The recipient’s immune system plays no active role.
 There is no lag or active period, the immunity is effective
immediately after passive immunization.
 There is no negative phase.
 It confers only transient immunity lasting usually for days or
weeks till the antibodies are metabolized & eliminated.
 There is no secondary type response. Rather subsequent
administration of antibodies is less effective due to immune
elimination.

17. Natural Passive
Immunity
Artificial Passive
Immunity

18.  NATURAL PASSIVE IMMUNITY
 This is the resistance transferred from mother to fetus
through placenta.
IgG antibodies can cross placental barrier to reach the
fetus.
After birth, immunoglobulins are passed to the newborn
through the breast milk.
 Human colostrum is rich in IgA antibodies which are
resistant to digestion in stomach & small intestine, hence
confers immunity on the neonate up to three months of
age.

19.  ARTIFICIAL PASSIVE IMMUNITY
This is the immunity transferred passively through
parenteral administration of antibodies .
The agents used for artificial passive immunity &
hyperimmune sera of animal or human origin,
convalescent sera & pooled human gammaglobulin.
For example, tetanus antitoxin is prepared in horses by
active immunization of horses with tetanus toxoid,
bleeding them & separating the serum.
These antitoxins are foreign proteins & are liable to
cause serious or even fatal hypersensitivity reactions,
these should be administered only after testing for
hypersensitivity.

20.  Sera collected from patients convalescing from infectious
diseases contain high levels of specific antibodies.
 Therefore, convalescent sera have been employed for
passive immunization against viral infections such as
measels & rubella.
 Sera of healthy adults contains antibodies against infectious
agents prevalent in a community. Therefore, sera from a
large number of individuals can be collected & used for
passive immunization.

21.  Placenta provides a convenient source of human
immunoglobulins.
 Human immune serum does not lead to hypersensitivity
reaction, there is no immune elimination & its half life is
more than that of animal serum.
 However, with immune serum there is a grave risk of
transmission of HIV & Hepatitis B,C & D viruses.

22.  To provide immediate short term protection in a non
immune host, faced with the threat of a serious infection.
 For suppression of active immunity which may be injurious.
Example, to use Rh immunoglobulins during delivery to
prevent immune response to RH factor in Rh negative
mothers with Rh positive babies.
 For treatment of serious infections.

23.  Live vaccines
oBCG for Tuberculosis
oSabin vaccine for poliomyelitis
oMMR vaccine for measels, mumps, rubella
 Killed vaccines
oTAB for enteric fever
oNeural & non-neural for rabies
oHepatitis B vaccine
oSalk vaccine for poliomyelitis
oKilled cholera vaccine

24.  Bacterial products
oTetanus toxoid for tetanus
oDiptheria toxoid for diptheria

26.  A combination of active & passive immunisation is
employed simultaneously which is known as combined
immunisation.
 Passive immunisation provides the protection necessary till
the active immunity becomes effective.
 Diptheria antitoxin & Diptheria toxoid can also be practiced
similarly.

27.  This means immunity at a particular site, generally the site of
invasion & multiplication of pathogen.
 For example, in case of poliomyelitis, parenteral vaccine
provides systemic immunity.
 Natural infection or the live viral vaccine administered orally
or intranasally (live influenza vaccine) provide local
immunity while killed influenza vaccine evokes humoral
antibody response.
 Local immunity is conferred by secretory IgA antibodies
produced locally by plasma cells present on mucosal surfaces
or in secretory glands.

28.  It refers to the overall resistance in a community.
 When a large number of individuals in a community are
immune to a pathogen the herd immunity to a pathogen is
said to be satisfactory.
 When herd immunity is low, chances of epidemics increase
on introduction of a suitable pathogen.
 Eradication of any communicable diseases depends on
development of a high level of herd immunity rather than of
immunity in individuals.

29.  Injection of immunologically competent lymphocytes is
known as adoptive immunity. Instead of whole
lymphocytes, an extract of immunologically competent
lymphocytes known as transfer factor can be used.
 This has been attempted in the treatment of lepromatous
leprosy.

30.  Immunoprophylaxis is the prevention of disease by the production of
active or passive immunity.
 Immunoprophylaxis against viral illnesses includes the use of
vaccines or antibody.
 The incidence of diseases, such as diphtheria, measles, mumps,
pertussis (whooping cough), rubella (German measles), poliomyelitis,
and tetanus, has declined dramatically as vaccination has become
more common.

31.  The exaggerated immune response produced by the body to protect a
person from foreign bodies.
 Antigen detected by the immune system starts
a hyperimmune response and the hypersensitivity reaction starts.
 It leads to various consequences ranging from mild symptoms to
severe shock causing death.

32.  Food: nuts, eggs, soy, wheat, shellfish, etc.
 Animal source: bee, wasp, cats, insects, rats, etc.
 Environmental factors: dust mites, latex, pollen, mold,
etc.
 Atopic diseases: allergic asthma, allergic rhinitis,
conjunctivitis, dermatitis, etc.
 Medication-induced reactions: antibiotics.

33. TYPE HYPERSENSITIVITY Antibodies or
cell mediators
Examples
I •Allergy
•Immediate
•Anaphylactic
Ig E •Atopy
•Anaphylaxis
II Antibody-dependent Ig M
Ig G
•Autoimmune hemolytic
anemia
•Rheumatic heart disease
•Thrombocytopenia
III Immune complex Ig G
Neutrophils
•Serum sickness
•Rheumatoid arthritis
IV •Delayed
•Antibody-independent
•Cytotoxic
T- cells •Contact dermatitis
•Mantoux test

34.  When the body's immune system mistakes its own healthy tissues as
foreign and attacks them, this is called autoimmunity.
 Autoimmune diseases cause inflammation that affects many parts of
the body.
 The parts of the body affected depend on which autoimmune disease a
person has.
 Cause- Not known.
◦ A combination of factors known are-
 Genes which may make you more likely to develop the disease.
 A virus that triggers the disease if you have the gene.
 The most common Autoimmune Disorders include:
◦ Crohn's Disease.
◦ Diabetes Type 1.
◦ Multiple Sclerosis.
◦ Rheumatoid Arthritis.

35.  A laboratory test that checks for the presence of antibodies or
other substances in a blood sample.
 Serology tests are used to determine whether a person had a
past exposure to a pathogen. The tests look for antibodies,
which can bind to the pathogen, that were formed as part of
the immune response.
 Rapid serology test (RST): This is a qualitative (positive or
negative) test. These tests may use blood from a finger prick, saliva,
or nasal swab fluids. The test shows the user colored lines to indicate
positive or negative results. In some cases, it can be beneficial to
measure of IgG and IgM titers.
 Enzyme-linked immunosorbent assay (ELISA)