The immune system has two main lines of defense - innate (non-specific) and adaptive (specific). The innate system provides immediate protection and involves physical and chemical barriers like skin and stomach acid. If pathogens breach these barriers, the second line uses phagocytes, natural killer cells, and inflammation to attack invaders. The adaptive system has a delayed but stronger response that involves lymphocytes. It distinguishes self from non-self and has immunological memory, providing lifelong protection against reinfection.
2. IMMUNOLOGY AND THE IMMUNE SYSTEM
• Immunology
– Study of the components and function of the immune system
• Immune System
– Molecules, cells, tissues and organs which provide non-specific
and specific protection against
• Microorganisms
• Microbial toxins
• Tumor cells
– Crucial to human survival
– Antigens :
– Molecules from a pathogen or foreign organism that provoke a
specific immune response.
3. The Invaders . . .
• Bacteria
• Viruses
• parasites
such as fungi,
protista, &
worms
worm trichura.jpg
http://www.hhs.gov/asphep/presentation/images/bacteria.jpg
http://www.skidmore.edu/academics/biology/plant_bio/lab13.FUNGI.html
4. Types Of Immune System
• Immune response
– Innate (non-specific)
– Adaptive (specific)
• Primary
• Secondary
• These two systems perform many of their functions
by cooperative interactions
6. Chapter 21, Immune System 6
Immunity: Innate (nonspecific)
• immunity an organism is born with.
• system responds quickly and consists of:
– First line of defense – intact skin and mucosae
prevent entry of microorganisms
– Second line of defense – antimicrobial proteins,
phagocytes, and other cells
• Inhibit spread of invaders throughout the body
• Inflammation is its hallmark and most important
mechanism
7. Chapter 21, Immune System 7
Immunity: Adaptive (specific) defense
system
– Third line of defense – mounts attack against
particular foreign substance.
– Immunity that an organism develops during life
time.
– Develops only after exposure to including agents
such as microbs, toxins, or other foreign
substances.
• Takes longer to react than the innate system
• Works in conjunction with the innate system
8. First line of defenses / innate immune
system
• The body’s 1st line of defense against pathogens uses mostly
physical and chemical barriers such as :
• Skin- acts as a barrier to invasion
• Sweat- has chemicals which can kill different pathogens.
• Tears – have lysozymes which has powerful digestive abilities
that render antigens harmless .
• Saliva – also has lysozymes
• Mucus – can trap pathogens, which are than sneezed,
coughed, washed away, or destroyed by chemicals
• Stomach acids – destroys pathogens .
11. Chapter 21, Immune System 11
Epithelial Chemical Barriers
• Epithelial membranes produce protective
chemicals that destroy microorganisms
– Skin acidity (pH of 3 to 5) inhibits bacterial growth
– Sebum contains chemicals toxic to bacteria
– Stomach mucosae secrete concentrated HCl and
protein-digesting enzymes
– Saliva and lacrimal fluid contain lysozyme
– Mucus traps microorganisms that enter the
digestive and respiratory systems
12. Chapter 21, Immune System 12
Respiratory Tract Mucosae
• Mucus-coated hairs in the nose trap inhaled
particles
• Mucosa of the upper respiratory tract is
ciliated
– Cilia sweep dust- and bacteria-laden mucus away
from lower respiratory passages
13. 1st line of defense (Respiratory and
Digestive System
• The respiratory passage is lined
with mucous
• Cilia also lines the respiratory
passage
• There is mucous in the
respiratory passage that traps
invading microbes and other
foreign debris with the cilia.
• Acids in the stomach and protein
digesting enzymes destroy most
of the invading microbes carried
into the body with food.
Immune System Overview:
Goals
14.
15. Second line of defense
• If a pathogen is able to get past the body’s
first line of defense, and an infection starts ,
the body can rely on it’s second line of
defense .
16.
17. Chapter 21, Immune System 17
Internal Defenses (Second Line of
Defense)
• The body uses nonspecific cellular and chemical
devices to protect itself
1. Phagocytes
2. natural killer (NK) cells
3. Inflammatory response enlists macrophages, mast
cells, WBCs, and chemicals
4. Antimicrobial proteins in blood and tissue fluid
• Harmful substances are identified by surface
carbohydrates unique to infectious organisms
18. Leukocytes• also called white blood cells are
large opaque blood cells that
engulf invading microbes. They
can also produce antibodies.
– They have a nucleus (so different
from red blood cells)
– The size of the nucleus and the
types of granules that can be
found inside of them can be used
to classify them into different
classes of leukocytes.
• Granulocytes: have cytoplasmic
granules and are made in the
bone marrow.
• Agranulocytes: do not have a
granular cytoplasm and are also
made in the bone marrow, but
then modified in the lymph
nodes.
20. Chapter 21, Immune System 20
1. Phagocytes
• Macrophages are the chief phagocytic cells
• Free macrophages wander throughout a region in search
of cellular debris
• Kupffer cells (liver) and microglia (brain) are fixed
macrophages
• Neutrophils become phagocytic when encountering
infectious material
• Eosinophils are weakly phagocytic against parasitic
worms
• Mast cells bind and ingest a wide range of bacteria
21.
22. Chapter 21, Immune System 22
Mechanism of Phagocytosis
• Microbes adhere to the phagocyte
• Pseudopods engulf the particle (antigen) into
a phagosome
• Phagosomes fuse with a lysosome to form a
phagolysosome
• Invaders in the phagolysosome are digested
by proteolytic enzymes
• Indigestible and residual material is removed
by exocytosis
24. Natural killer cells
Lymphocytes, such as NK cells, are
characterized by their large nuclei that
actively absorb Wright stain and therefore
appear dark colored under a microscope.
25. Chapter 21, Immune System 25
2. Natural Killer (NK) Cells
• Cells that can lyse and kill cancer cells and virus-infected
cells
• Natural killer cells:
– Are a small, distinct group of large granular lymphocytes
– React nonspecifically and eliminate cancerous and virus-
infected cells
– Kill their target cells by releasing perforins and other
cytolytic chemicals
– Secrete potent chemicals that enhance the
inflammatory response
26.
27. Chapter 21, Immune System 27
3. Inflammation: Tissue Response to
Injury
• The inflammatory response is triggered
whenever body tissues are injured
– Prevents the spread of damaging agents to nearby
tissues
– Disposes of cell debris and pathogens
– Sets the stage for repair processes
• The four cardinal signs of acute inflammation
are redness, heat, swelling, and pain
29. Chapter 21, Immune System 29
4. Antimicrobial Proteins
• Enhance the innate defenses by:
– Attacking microorganisms directly
– Hindering microorganisms’ ability to reproduce
• The most important antimicrobial proteins
are:
– Interferon
– Complement proteins
30. Interferon
• Protein secreted by a cell currently infected by a virus
• Interferon warns the neighboring cells of the impending viral
infection
• The neighboring cells synthesize proteins that will block the
virus from hijacking the cell DNA replication machinery
32. Chapter 21, Immune System 32
• Complement helps destroy pathogens
• in three ways:
• 1. Enhanced inflammation.
• Complement proteins are
• involved in and amplify the inflammatory response
• because certain ones can bind to mast cells (type of
• white blood cell in tissues) and trigger histamine
• release, and others can attract phagocytes to the
scene.
• 2.
Complement Pathways
33. Chapter 21, Immune System 33
2.Some complement proteins bind to the surface of
pathogens already coated with antibodies, which
ensures that the pathogens will be phagocytized by a
neutrophil or macrophage.
3. Certain other complement proteins join to form a
membrane attack complex that produces holes in the
surface of some bacteria and viruses. Fluids and salts
then enter the bacterial cell or virus to the point that it
bursts .
Complement systems
35. Chapter 21, Immune System 35
• Abnormally high body temperature in
response to invading microorganisms
• The body’s thermostat is reset upwards in
response to pyrogens, chemicals secreted by
leukocytes and macrophages exposed to
bacteria and other foreign substances
Fever
36. Chapter 21, Immune System 36
• High fevers are dangerous as they can
denature enzymes
• Moderate fever can be beneficial, as it causes:
– The liver and spleen to sequester iron and zinc
(needed by microorganisms)
– An increase in the metabolic rate, which speeds
up tissue repair
Fever
37. Adaptive Immunity
• Immunity that an organism develops during
lifetime
• Develops after exposure to antigens
• Invovles the activity of lymphocytes
• Includes 3rd line of defense
38. Adaptive Immunity (Specific immunity)
• Specificity
• Memory
• Ability to distinguish b/w self
vs non-self
• T and B cell
39. Types of Adaptive Immunity
1. Antibody-Mediated Immunity (AMI) or
Humoral Immunity
– B lymphocytes
2. Cell-Mediated Immunity (CMI) or Cellular
Immunity
– T lymphocytes
Note: B and T cells ……..blood, lymph, lymphoid
tissues such as spleen, lymph nodes etc.
40. Cell-Mediated Immune Response
• T cells
• Immune resoponse to infected cells
( viruses, bacteria and parasites (Pathogens) within
cells)
• Defense against cancer and transplant cells
Chapter 21, Immune System 40
41. T-Lymphocytes
• Helper T cells – secrete CYTOKINES
help B cells Tc cells to divide
• Cytotoxic T cells (killer T cells)
Kill infected body cells
• Memory T cells
remain in body
42. How do T cells know a cell is infected?
• Infected cells digest some pathogens and MHC
proteins carry pieces to cell surface
• Antigen Presenting Cell (APC)
• Alerts Helper T cells
MHC proteins displaying
foreign antigens
infected
cell
T cell with
antigen receptors
TH cell
45. Helper T Cells (TH)
• bind to other white blood cells that have
previously encountered an antigen
– stimulate proliferation of other T cells
– Stimulate B cells that have already become bound
to antigen
• Without TH, there is no immune response
Chapter 21, Immune System 45
46. The central role of Helper T Cells (Boss)
Chapter 21, Immune System 46Figure 21.17a
47. Cytotoxic T Cell (Tc)
• Destroys infected body cells
– binds to target cell
– secretes perforin protein
• punctures cell membrane of infected cell
– apoptosis
Chapter 21, Immune System 47
48. Cytotoxic T cells
Killer T cell
binds to
infected cell
• Destroys infected body cells
– binds to target cell
– secretes perforin protein
• punctures cell membrane of infected cell
– apoptosis
infected cell
destroyed
50. Cytotoxic T cell
1 2
Accessory
protein
Class I MHC
molecule
Infected
cell
Antigen
receptor
Antigen
fragment
Perforin
Pore
Gran-
zymes
51. The killing action of
cytoxic T cells on an
infected host cell.
Cytotoxic T cell
31 2
Accessory
protein
Class I MHC
molecule
Infected
cell
Antigen
receptor
Antigen
fragment
Perforin
Pore
Gran-
zymes
Released
cytotoxic
T cell
Dying
infected cell
53. • Human Immunodeficiency Virus
– virus infects and destroys helper T cells
• helper T cells don’t activate rest of immune system: killer T
cells & B cells
• AIDS: Acquired ImmunoDeficiency Syndrome
– infections by opportunistic
diseases
– death usually from
– “opportunistic” infections
• pneumonia, cancers
HIV & AIDS
HIV infected T cell
54. ANTIBODY-MEDIATED (HUMORAL) IMMUNITY
• targets extracellular microorganisms (Bacteria
and viruses circulating in the blood)
• B-lymphocytes (B cells)……….Antibodies
• Antibodies… extracellular fluids and surface of B
cells
58. Antibody-mediated (humoral) immunity = AMI
• 1- Macrophages phagocytize
a pathogen and present an
antigen to a matching helper-
T cell
• 2- At the same time, some
pathogens contact B-cells
matching the pathogen’s
antigens
• The helper-T cells multiply,
secrete lymphokines which
stimulate the B-cells to
multiply and specialize into
plasma cells
• The plasma cells secretes
antibodies
59. The Nature of Antibodies
• Globular proteins called immunoglobulins
• Basic antibody structure has 4 polypeptide chains
– 2 identical light chains
– 2 identical heavy chains
• Regions of heavy and light chains
– Variable
– Constant
63. Immunoglobin Classes
IgM
1st response to antigen
Can’t cross placenta
IgG
Most common form
Crosses placenta (passive
immunity to fetus)
IgA
Secreted from mucus membranes
In colostrum
IgD
B cell activation
Can’t cross placenta
IgE
Histamine reactions
and allergies
(mast cells,
basophils)
64. Types of Immunity
Active Immunity
Natural active immunity - acquired due to infection
Artificial active immunity – vaccination
Passive Immunity
Natural passive immunity
placenta to the fetus
Colostrum
Artificial passive immunity
Injection of immune serum