Immunity & Immune system

IMMUNITY & IMMUNE
SYSTEM
Dr. Pulipati Sowjanya
Professor & Head
Dept. of Pharmaceutical Biotechnology
Vignan Pharmacy College
Guntur

IMMUNITY
▪ The term immunity is derived from Latin
word “Immunis” means free from burden or
exempt
▪ In biology the burden is disease caused by a
Variety of micro organisms.
▪ EX:- viruses, bacteria, fungi, protozoa etc..
• Louis Pasteur is said to be the father of
Immunity.
• Edward Jenner gave the knowledge of
immunity and introduced the technique of
vaccination against smallpox.
18 October 2020 2VIGNAN PHARMACY COLLEGE, VADLAMUDI

CLASSIFICATION OF IMMUNITY
318 October 2020 VIGNAN PHARMACY COLLEGE, VADLAMUDI

Components of Immunity
Innate Immune System Adaptive Immune System
Response is non specific
Pathogen & antigen specific
response
Exposure leads to immediate
maximal response
Lag time between exposure and
maximal response
Cell-mediated and humoral
components
Cell-mediated and humoral
components
No immunological memory
Exposure leads to immunological
memory
Found in nearly all forms of life Found in vertebrates

Innate Host Defenses
A. Anatomical barriers to infections
1. Mechanical Factors
✓ Skin
Epidermis
Dermis
✓ Cilia or peristalsis help to keep air passages and GIT free from
microbes
✓ Flushing action of tears and saliva
✓ mucous that lines respiratory & GIT protects lungs & digestive
system

2. Chemical Factors
✓Fatty acids in sweat
✓Lysozyme & phospholipase found in tears, saliva and nasal
secretions can break cell wall of bacteria
✓Low PH of sweat & gastric secretions prevents growth
3. Biological Factors
The normal flora of skin & GIT can prevent the
colonization of pathogen bacteria by secreting toxic substances

B. Humoral barriers to infection
✓Complement system – Complement leads to increased
vascular permeability, recruitment of phagocytic cells and lysis.
✓Coagulation system – β-lysin protein produced by platelets
during coagulation can lyse many Gram+ve bacteria
✓Lactoferrin, transferrin – by binding to iron, an essential
nutrient for bacteria limit the bacterial growth
✓Interferons – these proteins limit viral replication in cells.
✓Lysozyme – break down the cell wall of bacteria

C. Cellular barriers to infection
Neutrophils
Macrophages
Natural Killer (NK) cells
Lymphokine Activated Killed cells (LAK)
These cells are the main line of defense in non specific
immune system

IMMUNE SYSTEM
The immune system comprises of
various cells and organs.
The organs are of two types:
❖ Primary lymphoid organs
Mammals -Thymus, bone marrow
Birds - Bursa of fabricus
❖ Secondary lymphoid organs
➢Spleen
➢Lymph nodes
➢Mucosal associated lymphoid
tissues (MALT)
18 October 2020 VIGNAN PHARMACY COLLEGE, VADLAMUDI 10

Thymus
➢The thymus develops from epithelium of
the third and fourth pharyngeal pouches at
6th week of gestation.
➢By the 8th week, mesenchymal stem cells
(precursors of lymphocytes) from the yolk
sac, fetal liver & bone marrow reach the
thymus and differentiate into thymocytes.
➢It reaches its maximal size just before
birth and continues to grow till about 12th
year.
11VIGNAN PHARMACY COLLEGE, VADLAMUDI18 October 2020

Contains 2 lobes surrounded by Capsule.
➢ Capsule divide the gland into lobules
which differentiated into
Outer Cortex
Inner Medulla
➢ Cortex consists of proliferating
lymphocytes
➢ Medulla consists of epithelial cells
and mature lymphocytes.
About 1% of the proliferated lymphocytes leave the
thymus and rest are destroyed locally.
Thymus

maturation
Thymus
❑ Thymus is the major site for
proliferation of lymphocytes.
❑ The primary function of the
thymus is the production of
T lymphocytes, responsible
for cell mediated immunity
and also humoral immunity
by TH cells.

Bone Marrow
It is a site of B cells and T cells.

Bursa of fabricius
▪ It is also a site of lymphocytic
proliferation and differentiation in birds.
▪ Stem cells from the yolksac, foetal liver
and bone marrow enter the bursa of
fabricius, proliferate and develop into
lymphocytes or B cells.
▪ B lymphocytes transform into plasma
cells and secrete antibodies.

Secondary lymphoid organs
• Lymphocytes differentiate and mature in the primary lymphoid
organs.
• They proceed Via Circulation to the secondary lymphoid
organs.
• They bind to antigen and undergo further antigen dependent
differentiation.
Organs under Secondary lymphoid are :
➢ Spleen
➢ Lymph nodes
➢ Mucosa associated lymphoid tissues (MALT)

SPLEEN
Spleen has a capsule from which trabeculae
descend, dividing the organ into two
compartments.
White pulp
Red pulp

18
• Spleen consists of both T and B cells.
• Spleen filters the blood and trap blood –
borne microorganisms and antigens and
carry out their immune functions.
• The spleen contains lymphocytes and
macrophages, which engulf and destroy
bacteria, dead tissue and foreign matter
and remove them from the blood passing
through the spleen.
SPLEEN

LYMPH NODE
❖These are Small bean
shaped organs containing
Outer cortex
Inner medulla
❖ The cortex consists of
lymphoid follicles where
as inner medulla consists
of medullary cords.

❖ In the cortex lymphoid follicles
develop during antigenic
stimulation.
❖ It possess lymphocytes, dendritic
cells, macrophages which capture
and process the antigen.
❖ In the medulla, the lymphocytes,
plasma cells and macrophages are
arranged as elongated branches
(medullary cords) contain B
lymphocytes.
❖ Lymph nodes filter out harmful
micro organisms and antigens.
LYMPH NODE

MALT
• Lymphoid tissues found in submucosal regions of the
body can be viewed as a Single functional unit called
‘Mucosa Associated Lymphoid tissue’.
• MALT contains Phagocytic cells and lymphoid cells (B
Cells and T Cells).
• The Predominant Ig Produced in the mucosa is secretary
IgA (SIgA).

TONSILS
Two masses of soft glandular tissue on either side or the back of the
mouth.
Function:
Traps bacteria and viruses from inhaled air.

APPENDIX
Thin, dead-end tube measuring about
three-to-four inches in length and it hangs
from the cecum.
Functions:
Help the lymphocytes exactly where they
have to head over to attack infection and
it also enhances the massive intestine's
defenses to a range of drugs and foods.

PEYER’S PATCHES
The nodules of lymphatic cells that combine to make patches or bundles and appear
generally only within the lowest part of intestine (ileum)
Functions:
Detect antigens such as bacteria and toxins and mobilize highly specialized white blood
cells termed B-cells to produce an antibody.

PEYER’S PATCHES

Cells involved in the Immune response

• Lymphocytes :
Lymphocytes are the main cell types which recognize the
antigen and elicit the immune response, both humoral and cell
mediated.
It was clearly demonstrated that lymphocytes are
converted into antibody producing plasma cells.
Functions of Lymphocytes :
✓ Recognition of antigen
✓ Storage of immunological memory
✓ Induction of immune response.
27
Cells involved in the Immune response

LYMPHOCYTES
Lymphocytes are divided into Three Types
➢T Lymphocytes
➢B Lymphocytes
➢Null Cells
• T and B Cells can be differentiated by their surface markers.
• Null Cells do not possess surface marker.

T - Lymphocytes
These cells have membrane receptors for antigen
T cells recognize Ag when it is bound to a self molecule encoded by genes
within MHC
After activation the cell divides to form:
• T-helper cells (TH) (CD4) – secrete cytokines
→ help B cells divide
→ stimulate macrophages
• Cytotoxic/Suppressor T cells (TC & TS) (CD8) - (killer/suppressor T cells)
→ Kill body cells displaying antigen
• Memory T cells
→ remain in body

❑TH cells are activated by recognition of antigen with Class – II
MHC molecules on an Ag-Presenting Cells (APC).
❑These TH cells secrete various cytokines which play a central role
in the activation of B cells.
❑The activated B cells differentiate into Plasma & Memory cells
T - Lymphocytes

T - Lymphocytes
Activates B- CellActivates Cytotoxic
T- Cell
Memory B-Cell
Memory T-Cell
Kills Infected Cells
Antibodies→
31

• B-Lympocytes mature at bursa of fabricius in birds and bone
marrow in mammals.
• Mature B cells distinguished from other cells by their synthesis &
display of membrane bound Ig, which serve as receptor for Ag
• CD45 – Used as marker for B cells and their precursors
• CD35 – Receptor for complement fixation
• Class – II MHC – Permits B – cells to function as an Ag Presenting
Cell (APC)
B – Lymphocytes

B – Lymphocytes
• Interaction between Ag and membrane bound antibody on naïve B
cell, T –cells & macrophages induce the differentiation of B cells
into plasma and memory cells
• The PLASMA CELLS produce lots of antibodies and they stay in
the blood longer but eventually their numbers go down too.
• MEMORY CELLS divide rapidly as soon as the antigen is
reintroduced.
• When the pathogen/infection infects again it is destroyed before any
symptoms show.

B – Lymphocytes

Null Cells
• Null cells are a small proportion (5%) of lymphocytes that
lack the surface markers.
• They are non phagocytic but can kill malignant, Virus
infected and transplanted cells by direct cytotoxic action.
Null Cells are divided into three types :
▪ Natural Killer Cells (NK)
▪ Killer Cells (K)
▪ Lymphokine Activated Killer (LAK) Cells.

Natural Killer Cells (NK)
Natural Killer Cells:
• NK cells are important in immune surveillance and natural defense against
virus infected and malignant cells.
• T and B cells are absent
Killer Cells :
• They are capable of killing or lysing target cells sensitized with IgG
antibody
Lymphokine Activated killer (LAK) cells:
• These null cells are NK cells treated with interleukin-2(IL-2).
• LAK cells can be used in the treatment of some tumors such as renal cell
carcinoma

Macrophages (or) Phagocytes
• Larger than neutrophils.
• Found in the organs, not the blood.
• Made in bone marrow as monocytes, called
macrophages once they reach organs.
• Long lived
• They develop immunity by phagocytosis
process.

PHAGOCYTOSIS

❖ Short life span. Circulate in blood for 7 – 10 hrs & migrate to tissue spaces
❖ Neutrophils accounts 54 – 74% of WBC’s. The no. increases during
infection
❖ The nucleus is segmented into 3-5 connected lobes, hence named as
polymorphonuclear leukocyte.
❖ Their cytoplasm contains granules – azurophilic & specific granules, hence
granulocytes and does’t stain with either acidic or basic dyes.
❖ Specific granules contain bactericidal substances – lysozyme, collagenase,
lactoferrin.
❖ Azurophilic granules are lysosomes.

❑Like neutrophils they are motile, phagocytic cells and migrate
from blood to tissue.
❑The nucleus is segmented into 2 lobes.
❑Found in large numbers in allergic inflammation, parasitic
infections.
❑Granules have hydrolytic enzymes which kills large parasites.
❑Cytoplasm stains with acid dye eosin red.

❖Found in blood & tissues.
❖Non-phagocytic
❖Granules containing heparin, histamines, serotonin and other
hydrolytic enzymes.
❖Play an important role in allergic responses.
❖Cytoplasm stains with basic dye – methylene blue.

❖Originate in bone marrow & release into blood by haematopoiesis.
❖Present as undifferentiated cells in blood and differentiate in tissues.
❖Found in skin, connective tissues of organs, mucosal epithelial
tissues of respiratory & digestive tracts.
❖Like basophils contains granules containing histamine and other
pharmacologically active substances.
❖Mast cells with basophils play an important role in development of
allergies.

➢These are derived from myeloid progenitor in the bone marrow.
➢They have the long membrane extensions that resembles dendrites of
nerve cells.
➢They capture and transport antigen to the draining lymph node.
➢During their migration to the lymph node, dendritic cells mature into
APC.
➢Mature dendritic cells reside in T cell area (paracortex) of lymph node.
➢They present Ag to TH cells.
➢Based on their location there are four types
Langerhan dendritc cells – epidermis & mucous mem
Interstitial dendritic cells – heart, lungs, liver, kidneys
Circulating dendritic cells – blood
Interdigitating dendritic cells – T cell area of 20 lymphoid tissue

Granulocytes

CONCLUSION
The immune system is one of nature's
more fascinating inventions.
With ease, it protects us against billions of
bacteria, viruses, and other parasites.
Most of us never reflect upon the fact that
in every aspect (breath, eat or drink) inside our
bodies, our immune system is constantly on the
alert, attacking at the first sign of an invasion by
harmful organisms and fight with foreign
invaders.

References
1. RamReddy, Textbook of Microbiology, Volume-III (Pg. 9-25 )
2. S.B. Sullia & S.Santharam, General Microbiology, (Pg. 415,418 )
3. Guyton and Hall, Textbook of Medical Physiology, (Pg. 444 )
4. Harshmohan, Textbook of Pathology, ( Pg. 68 )
5. S.P.Vyas and V.K.Dixith, Pharmaceutical Biotechnology, ( Pg.
456)
6. Ananthanarayan & Paniker’s, Text book of Microbiology 7th
Edition (Pg.117-129)

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