Immunity is the body's resistance or action against invaders or harmful substances. There are two types of immunity - innate (non-specific) and acquired (specific). The innate immunity provides first and second line of defense through physical barriers and white blood cells. The acquired immunity provides third line of defense through humoral immunity via B cells and antibodies or cell-mediated immunity via T cells. Edward Jenner is considered the father of immunology. Vaccines help develop acquired immunity by introducing weakened pathogens.

1. IMMUNITY

2. INTRODUCTION
The resistance or action of body against
invaders or harmful substances is called as
immunity.
The branch of zoology dealing with all
aspects of immunity is immunology.
 EDWARD JENER (1798) is father of
immunology.

3. TYPES OF IMMUNITIES IN BODY
Innate / Non-specific / Primary immunity
First line of defence – Physical barriers
Second line of defence – Internal
immunity
Acquired / Specific immunity
Third line of defence
Humoral immunity – B cell
Cell Mediated immunity – T cell

4. FIRST LINE OF DEFENCE
 Outermost layer of skin having dead cells prevents
entry of microbes.
 Sweat from sweat glands, oil from sebaceous
glands, acids and other metabolic wastes of
friendly bacteria on skin prevent growth of other
pathogens on it.
 Mucous of inner lining of digestive, respiratory &
urinogenital tract traps entering microbes.
 Mesh of fine hairs on nostrils filter particles from
inspired air.
 Sticky mucous secreted by cells of bronchi and
bronchioles trap microbes in inhaled air.
 Lysozyme, present in sweat, tear, saliva, nasal
discharges destroy bacterial cell wall and kill them.

5. SECOND LINE OF DEFENCE
Leuco
cytes
Normally human blood contains about
7000 to 8000 WBCs per cubic mm of blood.
Neutrophils (67 – 70 %), engulf foreign
bacteria. Basophils (0.5 – 1 %), engulf dust
particles and carbon. Eosinophils (3 %)
neutralise bacterial toxins and engulf
particles from antigen antibody reactions.
Lymphocytes (28 %) form antitoxins
causing wound healing. Monocytes (1.5 %)
ingest foreign living pathogens, remove
dead cells & produce antibodies.

6. Macro
phages
They may be fixed / wandering. Each can
engulf at least 100 bacteria.
Perfori
ns
It is a protein released from natural killer
cells. It kills the infected cell / cell into
which virus has entered. It make a hole in
plasma membrane, it allow entry of
water, cell swells and bursts.
Basic
polype
ptides
Some cells have these with antimicrobial
properties against specific microbes as
Bacillus anthracis.

7. Infla
mma
tion
The local changes in infected tissue
are collectively called inflammation. It
has five signs red, hot, swelling, pain
and fever in severe case. Histamine
released from broken mast cells, dilate
nearby blood vessels. It increases
more blood flow into infected tissue
causing redness and warmth. Fluid
released from damaged cells causes
swelling. Injury causes filling of pain.
Increased blood flow brings more
phagocytes that engulf microbes.

8. Fever Increased number of WBCs and
macrophages causes fever. Macrophages
release endogenous pyrogen or interleukin-
I that stimulate thalamus to maintain high
temperature causing fever. This is to
inhibit growth of microbes.
Comp
lemen
t-al
Protei
ns
These are secreted in liver. May rupture
cell membrane of microbes or tumour
cells. May stimulate mast cells to release
histamine causing inflammatory response.
May attract phagocytes to infected area.
May form a coat around pathogen for easy
phagocytosis.

9. Inter
feron
s
Almost all body cells produce δ & β
but specific lymphocytes and natural
killer cells produce γ interferons.
These are antiviral proteins released
by dead or infected cells. They enter
nearby uninfected healthy cells to
prevent viral infection in them.
Interferons produced by WBCs,
fibroblasts are not virus specific but
host specific.

10. THIRD LINE OF DEFENCE
Humoral Immune System – B – Cell
This system is based on B cells or B
lymphocytes or Bursa or bone marrow
derived cells.
They are formed and matured inside bone
marrow.
B cells have a life span of 5 – 7 days. With
blood, they enter lymph nodes as spleen,
thymus, tonsils etc.
They are activated by helper T cells upon
contact with the antigen. If not, die soon.
 ANTIGEN is a foreign agent that can initiate

11. an immune response.
Antigen may be a protein, lipoprotein or
polysaccharide molecule of the pathogen.
 Different parts of invader having such
markers are called ANTIGENIC
DETERMINATION SITES, each serving as a
separate antigen.
B cells produce ANTIBODIES in response to
antigen and react.
Antibody react with antigen by a process
called AGGLUTINATION.
It may inactivate antigen for ever or kill it or
destroy it. If antibody recognise antigen for

12. phagocytosis, it is called as OPSONISATION.
 COMPLEMENT MEDIATED CELL LYSIS –
immunoglobulin form pores in antigen and
breaks it.
Humoral immune system protects against
measles, small pox, cholera, cold, influenza
and tetanus.
Antibodies are proteins and collectively called
IMMUNOGLOBULINs.

13. IMMUNOGLOBULINS
Each immunoglobulin contains 4
polypeptide chains, 2 long / heavy / 
(kappa) & 2 short / light /  (lambda).
The chains are held together by disulphide
bonds to form a Y shaped molecule.
Top two tips of this Y bind to specific
antigen to form ANTIGEN – ANTIBODY
COMPLEX.
 Antigens may be destroyed by
agglutination / opsonisation / Complement
mediated cell.

14. 1 IgA
Secreted in gut, respiratory & urinogenital
tract, present in milk. Prevents attachment
of pathogens to epithelial cells and mucosal
surfaces.
2 IgD
Uncertain function. Helps in B cell
activation.
3 IgE
Against allergens. Stimulate release of
histamine for allergic and inflammatory
response.
4 IgG
Gama, most abundant plasma antibody. It
only can cross placenta. Provides passive
immunity to foetus.
5 IgM Specific against bacteria and virus.
TYPES OF IMMUNOGLOBULINS

15. WORKING OF B – CELL
Pathogen enters into body
Macrophage brings antigen from pathogen to
lymph node
Competent B cell comes in contact of antigen
Helper T cell activates B cell in presence of
antigen
Activated B cell multiply by mitosis to form
clones

16. Some become plasma cells Some become
memory B cells
Plasma cell secrete specific
antibodies
Continue to
secrete
antibodies for
many years
Antibodies are transported by
blood and lymph to infected region O
They react with antigen of
pathogen to form antigen –
antibody complex
R
Response
rapidly if same
infection
reoccurs
Destroy / inactivate pathogen as
needed

17. THIRD LINE OF DEFENCE
Cell Mediated Immune System – T – Cell
This system is based on T cells or T lymphocytes.
They are formed inside bone marrow and
matured inside Thymus hence name T.
In thymus T cells proliferate and become
sensitive and recognise particular antigen.
 CMI is against leprosy, tuberculosis and cancer.
T cells are smaller and live for months to years
to life long.
T cells have antigen specific receptor molecule
on surface.
On contact of specific antigen, T cells proliferate
to act as needed.

18. FIVE TYPES OF T – CELLS
Effector T cell ( Te / TDTH ) :- These are for
Delayed Type of Hypersensitivity Reactions.
Killer / Cytotoxic T cell ( Tc / Tk ) :-
These may be induced artificially by
immunisation with allogenic tissue and naturally
by tumours and viruses.
For this, precursor must be stimulated by
antigen and class II MHC ( Major
Histocompatibility Complex ) molecules, found
on 6th chromosome.
Tk release enzyme and kill pathogen.
Helper T cell ( Th ) :- They activate B cells in

19. presence of particular antigen.
Memory T cells ( Tm ) :- They are induced by
first contact of an antigen and ready for rapid
action in further contact of same antigen.
Suppressor T cell ( Ts ) :- They suppress
autoimmunity & activated by antigen associated
with class II MHC molecules.
** T cells release proteins called cytokines /
lymphokines / interlukins. Interlukin-1 released
by Macrophage and T cells is needed for
activation of Tc. Interlukin-4 helps in cloning and
activation of B cells.

20. WORKING OF T – CELLS
Pathogen enters into body
A competent small T cell is activated by
specific antigen on pathogen
Activated T cell increase in size
Activated T cell multiply by mitosis to form
clones

21. Some become Tc or Th
They leave lymph nodes
and migrate to site of
infection
Tc release lytic enzymes /
Th activate B cells or
stimulates macrophages
Pathogen is killed /
destroyed
Some become
memory T
cells
Remain in
lymph nodes
Response
rapidly if
same
infection
reoccurs

22. CHARAC
TER
ACTIVE /
OWN
IMMUNITY
PASSIVE /
ACQUIRED
IMMUNITY
Developm
ent
After
infection in a
person
By antibodies
acquired from
others.
Example
Immunity
after
vaccination,
after measles.
Immunity of
foetus by maternal
antibodies via
placenta or
colostrum ( thick
first milk )

23. AUTOIMMUNITY
It is a condition when B / T cells response
to certain antigens produced by body’s
own cells.
Hasimoto’s disease – thyroid is destroyed,
rheumatic fever – heart and joint affected.
Glomerulonephritis – glomerulus
membrane affected.
Multiple sclerosis – myelin sheath affected.

24. VACCINATION
Vaccine contain dead or weakened
pathogens or their products.
When introduced into a person, it causes
production of antigen specific actions and
memory cells but not the illness.
It is to develop acquired immunity.
Introduction of vaccine to a person is
called as vaccination.
Introduction of antigen or pathogenic
fragment to a person is called as
immunization.

25. THREE TYPES OF VACCINATION
Attenuation :- Repeatedly infecting cells
with antigen until its toxic effects is
reduced. Preparing snake venom using
horse, resistance of Chandragupta to
poison.
Peptide Fragments :- Capable of
producing immune response but not
illness.
DNA Vaccine :- Introducing a gene
encoding antibody for an antigen into
body.

26. ALLERGY
Allergy is the hyper reactivity of immune
system to a substance. They are ALLERGENS.
Allergens are mild antigens. IgE reacts to them.
Pollen, dust and such particles may be
allergens.
When an allergen is inhaled or eaten, it causes
release of histamine & serotonin from mast
cells.
They cause dilation of blood vessels causing
inflammatory response and irritation.
Allergy may be treated with antihistamine
drugs, adrenaline or steroid.

27. IMMUNODEFICIENCY
It is the deficiency of immune response in the body.
It may have symptoms like recurrent and chronic
infection, unusual infecting agents and poor
response to treatment.
It is of four types :-
Phagocytic Deficiency :- Both quantitative and
qualitative deficiency of phagocytes.
B-cell Deficiency :- Deficiency of B cell or Helper
T cell. In infants of 5-9 months.
T-cell Deficiency :- Due to absence of thymus &
parathyroid glands. e.g. AIDS.
Combined B-cell & T-cell Deficiency :- e.g. SCID
( Severe Combined Deficiency Disease ).

28. IMMUNE SYSTEM OF BODY
The system in body that protects it from
various infections is called immune system.
It consists of lymphoid tissues, its cells and
their products – antibodies.
Origin, maturation and multiplication of
lymphocytes occur in lymphoid organs.
Lymphoid organs may be :-
Bone marrow :- It is present in cavities of
long bones. It produce lymphocytes.
Thymus :- It is present below breast bone
near heart. Here maturation of T cells
occurs.

29. Spleen :- It lie below stomach in U shaped
limbs of duodenumto store Lymphocytes
& phagocytes.
Lymph nodes :- These are solid organs of
lymphoid tissues. They store B cells.
Mucosal Associated Lymphoid Tissues
(MALT) :- These are lymphoid tissues
present in gut, respiratory and
urinogenital tract.

30. MONOCLONALANTIBODIES
These are homogeneous immunological
reagents with defined specificity.
They are made from only one type of B
cells.
Production of MA / Hybridoma
Technology :- Given by Georges J. F.
Kohler and Cesar Milstein in 1975, Nobel
prize in 1984. These are produced by
fusing B cells with tumour cells to form
hybrid cells called hybridoma. They can
produce particular antibody.B cells can’t

31. divide once started producing antibodies
and are of short life span. It is overcame
by this technology.
Applications of MA :- Diagnosis, screening
and treatment of diseases. Production of
vaccines and vaccination. Used as enzymes
called abzymes. Antibody may bind to
specific ligands, antibodies may be
generated by modifying such ligands and
they catalyse specific reactions as enzymes.