Ch. 43 The Immune System notes

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Ch. 43 The Immune System
Objectives
LO 2.28 The student is able to use representations or models to
analyze quantitatively and qualitatively the effects of
disruptions to dynamic homeostasis in biological systems.
LO 2.29 The student can create representations and models to
describe immune responses.
LO 2.30 The student can create representations or models to
describe nonspecific immune defenses in plants and animals.
LO 2.34 The student is able to describe the role of programmed
cell death in development and differentiation, the reuse of
molecules, and the maintenance of dynamic homeostasis.
Overview
• Innate Immunity –
defenses are activated
immediately upon
infection; same
response for all
pathogens.
• Adaptive (Acquired)
Immunity – defenses
based on recognition
of the pathogen.
Pathogens
(such as bacteria,
fungi, and viruses)
INNATE IMMUNITY
(all animals)
• Recognition of traits shared
by broad ranges of
pathogens, using a small
set of receptors
Barrier defenses:
Skin
Mucous membranes
Secretions
• Rapid response
Internal defenses:
Phagocytic cells
Natural killer cells
Antimicrobial proteins
Inflammatory response
ADAPTIVE IMMUNITY
(vertebrates only)
Humoral response:
Antibodies defend against
infection in body fluids.
• Recognition of traits
specific to particular
pathogens, using a vast
array of receptors
• Slower response
Cell-mediated response:
Cytotoxic cells defend
against infection in body cells.
Ch. 43.1 In Innate Immunity, Recognition and Response
Rely on Traits Common to Groups of Pathogens
Invertebrates
• Exoskeleton (chitin)
• Chitin-based barriers and lysozymes
(break down bacterial walls) in
intestines
• Hemocytes
– Phagocytosis
– Chemicals
– Antimicrobial peptides (disrupt fungi
and bacterial plasma membranes)
– Specialized recognition proteins
Pathogen
PHAGOCYTIC
CELL
Vacuole
Lysosome
containing
enzymes
Vertebrates
• Barrier defenses
– Skin
– Cilia: sweep mucus and any entrapped microbes
upward, preventing the microbes from entering the
lungs
– Lysozymes in
• Mucus – traps microbes
• Saliva
• Tears
– Acidic
• Skin
• Sweat
• Stomach juices
• Cellular Innate Defenses
– Phagocytosis after Toll-like receptor recognizes
pathogen
•
•
•
•
Neutrophils: circulate in blood
Macrophages: live in cells/organs (spleen)
Dendritic cells: tissue in contact with environment (skin)
Eosinophils: beneath mucosal surfaces; multicellular
pathogens.
– Natural Killer Cells: secrete chemical when they come
in contact with a pathogen
• Antimicrobial Peptides and Proteins
– Interferons
• Made by virally infected cells to warn surrounding cells.
• Inflammatory Response
Pathogen
Mast
cell
Splinter
Signaling
molecules
Macrophage
Capillary
Movement
of fluid
Phagocytosis
Neutrophil
Red
blood cells
– Histamine is released by mast cells in response to tissue damage
• Trigger dilation and increased permeability of nearby capillaries
• Increased blood flow delivers clotting factors to the injury (marks
beginning of repair process/blocks spread of microbes)
– Cytokines from macrophages/neutrophils promote blood flow causing
redness and increased temp in the area.
– Pus—the accumulation of dead phagocytic cells and fluid leaked from
capillaries
43.2 In Adaptive Immunity, Receptors
Provide Pathogen-Specific Recognition
• Pathogens have antigens that trigger lymphocytic responses.
– B cells
• Binding of Y shaped antigen receptor on membrane to antigen causing it to
secrete soluble receptors called antibodies.
– T cells
• Single rod shaped antigen receptor only binds to already infected host cells that
display the antigen.
Antigen
receptor
Antibody
Displayed
antigen
fragment
B cell
Antigen
Epitope
T cell
T cell antigen
receptor
MHC
molecule
Pathogen
(a) B cell antigen receptors and antibodies
Antigen
fragment
Antibody C
Antibody A
Pathogen
Antibody B
Host cell
Antigen
(b) Antigen receptor specificity
(a) Antigen recognition by a T cell
Characteristics of Adaptive Immunity
1. Immense diversity of lymphocytes and receptors.
–
> 1 million different B cell antigen receptors; 10 million different T
cell antigens; each cell carries a specific set of these
2. Self-tolerance.
–
Lymphocytes are tested; any with “self” receptors go through
apoptosis.
3. Once recognized, increasing the number of specific
lymphocytes for an antigen.
–
Active lymphocyte divides by mitosis making cloned effector cells
(begin fighting immediately; B=plasma cells; T= helper T cells and
cytotoxic T cells) and memory cells (long lived cells that activate if
antigen enters the body again)
4. Stronger and quicker response to previously encountered
antigens.
–
Memory cells
43.3 Adaptive Immunity Defends Against
Infection of Body Fluids and Body Cells
Cell-Mediated Immune Response (attacks infected body cells)
• Active helper T cells secrete cytokines which activate cytotoxic T cells.
• Cytotoxic T cells bind to infected host cells
– Secretes proteins that disrupt membrane integrity and trigger apoptosis.
– Once destroyed, antibodies attach to antigens from within the host cell.
Antigenpresenting
cell
Antigen fragment
Cytotoxic T cell
Released
cytotoxic
T cell
Pathogen
Class II MHC molecule
Accessory protein
1
Accessory
protein
Class I MHC
molecule
Antigen receptor
Antigen
receptor
Pore
Helper T cell

Infected
cell

Cytokines
1
2

Cytotoxic T cell
Cellmediated
immunity
Perforin
Antigen
fragment
2
Dying
infected cell
Granzymes
3
Animation: Helper T Cells
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Animation: Cytotoxic T Cells
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Humoral Immune Response (attacks pathogen)
•
•
•
•
Helper T cells activate B cells.
B cells divide into memory or plasma cells.
Plasma cells give secrete 2,000 antibodies/sec!
Antibodies:
Antigen-presenting
cell
Class II
MHC
molecule
Antigen
receptor
Pathogen
Antigen
fragment
B cell
Cytokines
Helper T cell
1
Memory B cells

Accessory
protein
2
Activated
helper T cell
Plasma cells
3
– Prevent the pathogen from infecting cells (neutralization)
– Increase phagocytosis due to easy recognition (opsonization)
– Complement system of proteins opens a pore in the pathogen causing water
to rush in the pathogen to lyse.
Activation of complement system and pore
formation
Opsonization
Neutralization
Complement proteins
Antibody
Formation of membrane
attack complex
Virus
Bacterium
Flow of water
and ions
Pore
Macrophage
Foreign
cell
Antigen
Secreted
antibodies
Humoral (antibody-mediated) immune response
Cell-mediated immune response
Key
Antigen (1st exposure)

Engulfed by
Antigenpresenting cell

Stimulates
Gives rise to


B cell
Helper T cell


Cytotoxic T cell
Memory
helper T cells



Antigen (2nd exposure)
Plasma cells
Memory B cells

Memory
cytotoxic T cells
Active
cytotoxic T cells
Secreted
antibodies
Defend against extracellular
pathogens
Defend against intracellular
pathogens and cancer
Active and Passive Immunization
• Active (cell mediated and humoral responses)
– Can be induced by vaccinations – weakened,
killed, or parts of pathogens to – to create
memory cells and can lead to immunization.
• Passive (passed on from mother to child for
first few months of life)
– Injection of antibodies from an immune animal to
a non-immune animal.
Immune Rejection
• Cells from another person’s body can be
recognized as foreign due to different
carbohydrate found on the cell membranes,
causing an immune response.
– Blood groups (ABO)
– Tissue and Organ Transplant
43.4 Disruptions in Immune System
Function Can Elicit or Exacerbate Disease
• Allergies
– Exaggerated responses to allergens.
• Autoimmune diseases
– Immune system does not recognize “self-cells”
•
•
•
•
Lupus
Arthritis
Diabetes
MS
Immunodeficiency Diseases
• Inborn immunodeficiency results from
hereditary or developmental defects that
prevent proper functioning of innate,
humoral, and/or cell-mediated defenses
• Acquired immunodeficiency develops later in
life and results from exposure to chemical and
biological agents
• Acquired immunodeficiency syndrome (AIDS)
is caused by a virus
Evolutionary Adaptations of Pathogens
Antigenic Variation
• Changes its antigens so the host does not recognize it
– Ex: Flu
Latency
• Inactive state which does not trigger an immune
response (lysogenic cycle).
Attacking the Immune System Itself
• HIV – attacks helper T cells preventing both cell
mediated and humoral responses to infections.
Cancer and Immunity
• The frequency of certain cancers increases
when adaptive immunity is impaired
– 20% of all human cancers involve viruses
• The immune system can act as a defense
against viruses that cause cancer and cancer
cells that harbor viruses
• In 2006, a vaccine was released that acts
against human papillomavirus (HPV), a virus
associated with cervical cancer.

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