This lecture is very important for nursing students and other health related students.

1. Immunity
Microbiology
By
Muhammad Iqbal
Lecturer
KMU

2. Objectives
At the end, the students will be able to:
• Define key terms
• Identify specific and non specific defenses
• Explain three lines of defenses
• Differentiate humoral and cell-mediated
• Differentiate humoral and cell-mediated
immunity
• Discuss phagocytosis process
• Discuss four types of acquired immunity
• Identify five classes of Igs and their functions
M. Iqbal, KMU

3. Key Terms
• Immunity: The ability of body to resist pathogens.
• Antigen: A substance that causes the formation
of antibodies. It is also called immunogen
• Antibody: A protein produced in the body in
response to an antigen.
• Resistance: The ability of body to fight off a
pathogen through specific and non-specific
pathogen through specific and non-specific
defenses.
• Specific Immunity:
The body’s defensive response is specific against
a specific pathogen.
• Non-specific Immunity:
Body defense that provides protection against any
kind of pathogen.
M. Iqbal, KMU

4. • Innate Resistance:
The non-specific defenses gifted by birth. e.g, Skin,
phagocytic cells, or inflammatory response.
• Susceptibility: The lack of resistance to a disease is
known as susceptibility.
• Hapten: A substance of low molecular weight that is
not antigenic itself except when combined with a
not antigenic itself except when combined with a
protein in the body. e.g, Penicillin drug, detergent.
• Phagocytosis: The process of engulfment and
digesting of an antigen by a phagocytic cell.
• Opsonization: The coating or tagging of an antigen
by complement proteins to enhance phagocytosis.
M. Iqbal, KMU

5. Immunity
Non specific
Physical
barrier
Inflammation
Phagocytes
Chemical
barrier
Specific
Humoral
Immunity
Cell-mediate
Immunity
barrier
(skin, mucous
membrane)
Phagocytes
(neutrophils,
macrophages),
(lysozyme,
HCl,
interferon)
Immunity Immunity
M. Iqbal, KMU

6. • Nonspecific Defense/immunity
– body’s primary defense.
– intact skin & healthy mucous membranes
– lysozyme (in saliva and tears) destroys bacteria
– stomach acid destroys ingested bacteria
– phagocytes engulf bacteria entering the body
– inflammatory response including fever
– Complement proteins in plasma
– Complement proteins in plasma
• Specific Defense/immunity
– directed against antigens, or molecules recognized
as foreign bodies.
– produces antibodies to destroy invader.
– memory cells develop and remain in circulation.
– Two main types of cells: B cells and T cells

7. Nonspecific cellular components
• Natural killer cells (NK cells):
Lymphocytes that can destroy other cells,
especially tumor cells and other infected
cells.
cells.
• Macrophages (phagocytes) often act as
antigen presenting cells (APCs).
• This is then identified by T cells.
M. Iqbal, KMU

8. Three Lines of Defenses
Three Lines of Defenses
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9. First Line of Defense
It is nonspecific Defense:
• Intact Skin: Forms mechanical barrier that prevents
entry of pathogens and other harmful substances
into body.
• Intact mucous membranes: Form mechanical
• Intact mucous membranes: Form mechanical
barrier that prevents entry of pathogens.
• Mucous: Traps pathogens in respiratory and
digestive tracts.
• Nasal hair: Filter and trap microbes in nasal
passage.
M. Iqbal, KMU

10. First Line cont…
• Gastric juice: Contains HCl that destroys
pathogens in stomach.
• Lysozyme: Found in tears and saliva that
Kills microbes.
Kills microbes.
• Urine: Flushes out lower urinary tract; and,
its lower PH also inhibits some microbial
growth.
M. Iqbal, KMU

11. Second Line of defense
• Nonspecific cellular and chemical defense
• Inflammatory response: Prevents spread of
harmful agents to adjacent tissues; promotes
tissue repair; release chemical mediators to
tissue repair; release chemical mediators to
attract phagocytes and stimulate third line of
immune response.
• Fever: It is systemic response initiated by
pyrogens (i.e. prostaglandin); elevetaed body
temperature inhibits microbial proliferation.
M. Iqbal, KMU

12. Second Line cont…
• Phagocytes: Engulf pathogens and contribute
immune response.
Antimicrobial proteins:
Interferon: Proteins released by virus
infected cells that protect uninfected cells from
infected cells that protect uninfected cells from
viral overtake; mobilize immune system.
Complement: Enhances phagocytosis by
opsonization, Lyses microbes, and intensifies
inflammatory and immune responses.
M. Iqbal, KMU

14. Third Line of defense
• It’s response is antigen specific, means differentiates
pathogens.
• Third line of defense consists of humoral and cell
mediated immune response.
• For each type of pathogen, the immune system
produces cells and antibodies that are specific for that
produces cells and antibodies that are specific for that
particular pathogen.
• They fight off pathogens and provide long term
immunity by keeping record of the antigen into its
memory.
• Secondary response is thus relatively rapid and
stronger than the primary response.
M. Iqbal, KMU

15. Humoral and Cell-mediated
• Humoral immunity (or antibody mediated):
involves the production of antibodies.
It is governed by B-lymphocytes.
• Cell mediated immunity: is governed by
• Cell mediated immunity: is governed by
T-lymphocytes which involve different
types of T-cells
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16. Cell mediated Immunity
• Cell mediated immunity Involves T-lymphocytes that
act against infected cell or foreign cell or tissue.
• T cells are produced in bone marrow but mature in
the thymus gland.
• Also regulate the activation and proliferation of other
immune system cells
immune system cells
• Cell mediated immune response is directed against
bacteria and viruses inside phagocytic cells or
infected host cells.
• This also causes rejection of implanted tissue.
• T lymphocytes proliferate into different types of cells
M. Iqbal, KMU

17. Types of T cells
• Helper T-Cells: Helper T cells also produce
chemicals called cytokines such as lLs, TNF, GM-
CSF and interferon. Activate macrophages and B
cells. Also activate Tc and NK cells.
• Cytotoxic T-Cells: destroy target cells on contact by
producing toxin (perforin) that lyses targeted cells.
producing toxin (perforin) that lyses targeted cells.
• Suppressor T-Cells: (also called regulatory T cells)
are involved in stopping the reaction once the
danger is finished.
• Memory T-Cells: are long-lived cells which give
long term immunity against that pathogen.
M. Iqbal, KMU

18. Humoral immunity
• B cells or B lymphocytes are responsible
for antibodies production.
• This provides resistance to bacteria and
viruses and bacterial toxins
viruses and bacterial toxins
• Antibodies or immunoglobulins that
recognize different types of antigens.
M. Iqbal, KMU

19. B cells cont…
• B cells are produced and matured in stem
cells of bone marrow.
• Mature B cells are found in lymphoid tissues
like spleen and lymph nodes.
• B cells Recognize antigen by antigen
receptors on cell surface.
• We make 100 million lymphocytes a day, so
equal number must die. This death of cells is
known as ‘Apoptosis’ or ‘programmed cell
death’
M. Iqbal, KMU

20. Activation of B cells
• Each B cell produces an antibody against a
particular antigen.
• When antigen comes in contact with B cells they
form plasma cells and B memory cells.
• Plasma cells start the production of antibodies
while Memory cells give long term immunity
against that pathogen by keeping its record.
• Antibodies start binding to antigen and thus
inactivate the antigens.
• Secondary response of immune system is quicker
and stronger than the primary one.
M. Iqbal, KMU

21. Immune tolerance
• Immune tolerance, or immunological tolerance, or
immunotolerance, describes a state of unresponsiveness of
the immune system to substances or tissue that have the
capacity to elicit an immune response. It contrasts with
conventional immune-mediated elimination of foreign antigens.
 Classification of Immune tolerance
 Classification of Immune tolerance
 Central tolerance e.g Thymus and bone marrow
 Peripheral tolerance e.g Lymph nodes
• This classification depends on where the state is originally
induced.
• The mechanisms by which these forms of tolerance are
established are distinct, but the resulting effect is similar.
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22. Importance
• Immune tolerance is important for normal
physiology.
• Central tolerance is the main way the
immune system learns to discriminate self
from non-self.
from non-self.
• Peripheral tolerance is key to preventing
over-reactivity of the immune system to
various environmental entities (allergens, gut
microbes, etc.).
M. Iqbal, KMU

23. Trade-offs between immune tolerance and resistance
Mode Cost Benefits
Elimination (resistance)
Pain, swelling, and
disruption of tissue function
by inflammation.
Tissue damage by
inflammatory mediators
(immunopathology)
High energy cost.
Risk of autoimmunity,
hypersensitivity, and allergy
Reduces pathogen burden
Neutralizes toxins and
eliminates dangerous
organisms.
Prevents parasitism
hypersensitivity, and allergy
Tolerance
Direct damage by pathogen
(toxins, digestion, etc.)
Energy and resources lost
to pathogen
Reduced tissue damage
from immune response.
Less selection pressure on
pathogens for resistance.
Promotes commensalism
Lower energy cost
M. Iqbal, KMU

24. Immunoglobulin (Ig)
Summary of Immunoglobulin Classes
Characteristic
s
IgG IgA IgM IgE IgD
Structure Monomer Dimer Pentamer Monomer Monomer
Location Blood,
Lymph,
Intestine
Secretions
(tears, saliva,
Mucus), intestine
Blood, Lymph,
B-cell surface
Bound to
mast and
Basophil
Blood, Lymph,
B-cell surface
•IgG - Gamma 2. IgM – Mu 3. IgA – Alpha 4. IgD – Delta 5. IgE - Epsilon
Immunoglobulins are glycoprotein molecules that are produced by plasma cells (B-cell
type) in response to an immunogen (antigen), which function as antibodies.
Intestine Mucus), intestine
Breast milk,
blood, lymph
Basophil
cells,
Blood
Placental
Transfer
Yes No No No No
Function Enhances
phagocytosi
s,
neutralizes
toxins and
viruses,
Protects
Localized
protection on
mucosal
surfaces
Lysis and
agglutination
of
microorganis
ms
Allergic
reactions
, Lysis of
parasitic
worms
Serum function
not known,
presence on
B-cells
functions in
initiation of
immune

25. Phagocytosis

26. Key Terms
• Chemotaxin:
A chemical produced by cells to attract
macrophages towards antigens.
• Chemotaxis: is the process by which
macrophages are attracted to microorganisms.
• Opsonization:
The labeling of antigen with serum protein to help
phagocytes in ingestion.
• Phagocytosis:
The process of digesting of an antigen by
phagocytic cell is known as phagocytosis M. Iqbal, KMU

27. The Process of Phagocytosis
The process or mechanism of phagocytosis
involves the following steps:
• Chemotaxis attract and direct motility of
phagocytic cells.
• Both Chemotaxis and opsonization help
• Both Chemotaxis and opsonization help
phagocytes to adhere to the microbial cells.
• Pseudopods of phagocytes engulf and ingest
microbes.
• Inside macrophage, the microbes are killed by
lysozymes and other oxidizing agents.
M. Iqbal, KMU