1. THE IMMUNE SYSTEM

2. Objectives:
The lecture aims to help the student to
Understand :
- The Nature of the immune system
- Types of the immune system
- Innate immune response
- Components involved in innate immune
response

3. IMMUNOLOGY and THE IMMUNE SYSTEM
• Immunology
– is the study of the immune system and is a very
important branch of the medical and biological
sciences. The immune system protects us from
infection through various lines of defence.
• Immune System
– Molecules, cells, tissues and organs which provide
non-specific and specific protection against
• Microorganisms
• Microbial toxins
• Tumor cells

4. ACTIVE IMMUNE DEFENSES
Innate Immunity
- invariant (generalized)
- early, limited
specificity
- the first line of
defense
Adaptive Immunity
- variable
- later, highly specific
- ‘‘remembers’’
infection
(Memory)

5. Innate Immunity
The term, Innate immunity, refers to the basic
resistance to disease that a species possesses
since the birth- the first line of defense against
infection.
The characteristics of the innate immune response
include the following:
-Responses are Broad-Spectrum (non-specific)
-There is no memory or lasting protective immunity
-There is a limited repertoire of recognition molecules

6. • Potential pathogens are encountered
routinely, but only rarely cause disease.
The vast majority of microorganisms are
destroyed within minutes or hours by
innate defenses. The acquired specific
immune response comes into play only if
these innate defenses are breached.

7. Innate immunity
consists of

8. INNATE IMMUNITY
Barriers
• Physical
– skin
– hair
– Mucous
– Respiratory tract
– Digestive tract
– Eyes
– Blood-brain barrier
• Chemical
– sweat
– tears
– saliva
– stomach acid
– Urine
– P- glycoprotein

9. Barriers
1- Anatomic (Physical) Barriers
2- Physiological Barriers
3- Chemical Barriers

10. 1- Anatomic (Physical) Barriers
• Skin (physical barrier, low pH due to lactic and fatty
acids)
epidermis - thin outer layer containing tightly packed
epidermal cells and keratin (water-proofing) completely
renewed every 15-30 days.
dermis - thicker inner layer contains sebaceous glands
associated with hair follicles - produce sebum which
consists of lactic and fatty acids maintaining a pH 3-5.
• Mucous membranes (ciliated epithelial cells; saliva,
tears and mucous secretions) - GI, urogenital,
respiratory tracts - collectively represents a huge surface
area.

11. 2- Physiological Barriers
• Temperature - normal body temperature
inhibits growth of many microorganisms.
• Elevated body temperature (fever) can
have a direct effect on pathogenic
microorganisms.

12. 3- Chemical factor
• Fatty acids, lactic acid
• Pepsin (digestive enzyme which hydrolyzes proteins)
• Lysozyme -hydrolytic enzyme found in mucous secretions - able to
cleave the peptidoglycan layer of the bacterial cell wall
• Anti-microbial substances which directly destroy microorganims:
cryptidins and defensins
a- cryptidins (produced in base of crypts of small intestine - damage
cell membranes)
b-defensins (produced within skin, respiratory tract - also damages cell
membranes) surfactant proteins A & D (present in lungs - function
as opsonins which enhance the efficiency of phagocytosis)

13. • Interferons - group of proteins produced by cells
following viral infection. Secreted by the cells, and then
binds to nearby cells and induces mechanisms which
inhibit viral replication.
• Complement - a group of serum proteins that circulate in
an inactive proenzyme state. These proteins can be
activated by a variety of specific and nonspecific
immunologic mechanisms that convert the inactive
proenzymes into active enzymes. The activated
complement components participate in a controlled
enzymatic cascade that results in membrane-damaging
reactions which destroy pathogenic organisms by
formation of a membrane attack comples (MAC).

14. • Acute phase proteins
– proteins in the plasma that increase during
infection and inflammation
– can be used diagnostically in many diseases
to give an indication of acute inflammation

15. INNATE IMMUNITY
Cellular response
• The types of cells involved are:
macrophages, neutrophils, natural killer
cells, mast cells and Dendritic cells

16. Macrophages engulf pathogens and dead cell remains
Neutrophils release chemicals that kill nearby bacteria,
neutrophils die after performing it’s function
• pus = They are dead neutrophils, tissue cells and
engulfed dead pathogens
Phagocytic cells include

17. Phagocyte migration
Neutrophils and macrophages recognize chemicals
produced by bacteria and migrate "toward the smell".
CELLS alive!

18. Macrophages
• WBCs that ingest bacteria, viruses, dead cells, dust
• most circulate in the blood, lymph and extracellular
fluid
• they are attracted to the site of infection by chemicals
given off by dying cells
• after ingesting a foreign invader, they “wear” pieces
of it called antigens on their cell membrane receptors
– this tells other types of immune system cells what
to look for

20. Macrophage ingesting yeast
This human macrophage, like the neutrophil, is a professional
"phagocyte" or eating cell (phago = "eating", cyte = "cell").
Here, it envelops cells of a yeast, Candida albicans. After
ingestion, the white cell must kill the organisms by some
means, such as the oxidative burst.
CELLS alive!

21. Neutrophils
• WBCs – are phagocytic, like macrophages
• neutrophils also release toxic chemicals that destroy
everything in the area, including the neutrophils
themselves, so when the neutrophil kills the pathogen, it
will dies as well (forming pus cells)

22. What triggers innate immune responses?
( How do phagocytes know what to eat?)
• Long-known that bacterial cell wall components
activate phagocytes
• Hypothesis-- microbes contains pathogen associated
molecular patterns (PAMPs) which are recognized by
pattern recognition receptors (PRRs)

23. Natural killer cells (NK cells)
• instead of attacking the invaders, they attack the
body’s own cells that have become infected by
viruses
• they also attack potential cancer cells, often before
they form tumors
• they bind to cells using an antibody “bridge”, then kill
it by secreting a chemical (perforin) that makes holes
in the cell membrane of the target cell. With enough
holes, the cell will die, because water rushing inside
the cell will induce osmotic swelling, and an influx of
calcium may trigger apoptosis.

24. Mast cells
• are found in tissues like the skin, near blood vessels.
• are activated after antigen binds to a specific type of
antibody called IgE that is attached to receptors on the
mast cell.
• activated mast cells release substances that contribute to
inflammation, such as histamine.
• mast cells are important in allergic responses but are also
part of the innate immune response, helping to protect
from infection.

25. Dendritic cells
• They act as messengers between the innate and the
adaptive immune systems.
• Their main function is to process antigen material and
present it on the cell surface to the T cells of the
immune system.

26. • Reference: Essential Clinical Immunology,
Cambridge University Press , by John B.
Zabriskie