1. 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.

2. Pathogens (such as bacteria, fungi, and viruses)
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)
• Rapid response
Recognition of traits shared by broad ranges of pathogens, using a small set of receptors •
Recognition of traits specific to particular pathogens, using a vast array of receptors
• Slower response
Barrier defenses:
Skin Mucous membranes Secretions
Internal defenses:
Phagocytic cells Natural killer cells Antimicrobial proteins Inflammatory response
Humoral response:
Antibodies defend against infection in body fluids.
Cell-mediated response:
Cytotoxic cells defend against infection in body cells.
ADAPTIVE IMMUNITY (vertebrates only)

3. Invertebrates Exoskeleton (chitin)
Ch 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

4. 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
Sweat
Stomach juices

5. 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.

6. Inflammatory Response
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
Pathogen
Splinter
Mast cell
Macro- phage
Capillary
Red blood cells
Neutrophil
Signaling molecules
Movement of fluid
Phagocytosis

7. 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.
Antibody
Antigen receptor
B cell
Antigen
Epitope
Pathogen
(a) B cell antigen receptors and antibodies
Antibody C
Antibody B
Antibody A
(b) Antigen receptor specificity
Displayed antigen fragment
MHC molecule
Antigen fragment
Pathogen
Host cell
T cell
T cell antigen receptor
(a) Antigen recognition by a T cell

8. Characteristics of Adaptive Immunity
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
Self-tolerance.
Lymphocytes are tested; any with “self” receptors go through apoptosis.
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)
Stronger and quicker response to previously encountered antigens.
Memory cells

9. Cell- mediated immunity
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.
Antigen- presenting cell
Pathogen
Antigen fragment
Class II MHC molecule
Accessory protein
Antigen receptor
Helper T cell
Cytokines
Cell- mediated immunity
Cytotoxic T cell 2 1 
Cytotoxic T cell 3 1 2
Accessory protein
Class I MHC molecule
Infected cell
Antigen receptor
Antigen fragment
Perforin
Pore
Gran- zymes
Released cytotoxic T cell
Dying infected cell

10. Animation: Helper T Cells Right-click slide / select “Play”
© 2011 Pearson Education, Inc.

11. Animation: Cytotoxic T Cells Right-click slide / select “Play”
© 2011 Pearson Education, Inc.

12. 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:
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.
Pathogen 3 1 2
Antigen-presenting cell
Antigen fragment
Class II MHC molecule
Antigen receptor
Accessory protein
Helper T cell
B cell
Cytokines
Activated helper T cell
Memory B cells
Plasma cells
Secreted antibodies 
Opsonization
Neutralization
Antibody
Virus
Bacterium
Macrophage
Activation of complement system and pore formation
Complement proteins
Formation of membrane attack complex
Flow of water and ions
Pore
Antigen
Foreign cell

13. Humoral (antibody-mediated) immune response
Cell-mediated immune response
Antigen (1st exposure)
Engulfed by
Antigen- presenting cell
Helper T cell
Memory helper T cells
Antigen (2nd exposure)
B cell
Plasma cells
Secreted antibodies
Defend against extracellular pathogens
Memory B cells
Memory cytotoxic T cells
Active cytotoxic T cells
Defend against intracellular pathogens and cancer
Cytotoxic T cell
Key
Stimulates
Gives rise to 

14. 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.

15. 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

16. 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

17. 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

18. 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.

19. 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.