1. CHAPTER 24 The Immune System
Modules 24.1 – 24.2

2. The Continuing Problem of HIV
Acquired immune deficiency syndrome (AIDS) is epidemic throughout much of the world
14,000 people are infected with the AIDS virus every day
HIV is the virus that causes AIDS
HIV is transmitted mainly in blood and semen
Former L.A. Laker Magic Johnson is one of 900,000 Americans who are HIV-positive

3. Our immune system is a specific defense system
It backs up several mechanisms of nonspecific resistance
HIV attacks the immune system
It eventually destroys the body’s ability to fight infection

4. NONSPECIFIC DEFENSES AGAINST INFECTION
24.1 Nonspecific defenses against infection include the skin and mucous membranes, phagocytic cells, and antimicrobial proteins
The body’s first lines of defense against infection are nonspecific
They do not distinguish one infectious microbe from another

5. Macrophages wander in the interstitial fluid
They “eat” any bacteria and virus-infected cells they encounter
Figure 24.1A

6. Interferon and complement proteins are activated by infected cells
Viral nucleic acid
VIRUS 6
Antiviral proteins block viral reproduction 1 2
Interferon genes turned on
New viruses
mRNA 3 5
Interferon stimulates cell to turn on genes for antiviral proteins
Interferon molecules
HOST CELL 1
Makes interferon; is killed by virus 4
HOST CELL 2
Protected against virus by interferon from cell 1
Figure 24.1B

7. 24.2 The inflammatory response mobilizes nonspecific defense forces
Tissue damage triggers the inflammatory response
Skin surface
Swelling
Pin
Phagocytes
Bacteria
Phagocytes and fluid move into area
Chemical signals
White blood cell 1
Tissue injury; release of chemical signals such as histamine 2
Dilation and increased leakiness of local blood vessels; migration of phagocytes to the area 3
Phagocytes (macrophages and neutrophils) consume bacteria and cell debris; tissue heals
Figure 24.2

8. The inflammatory response can
disinfect tissues
limit further infection

9. The lymphatic system is a network of lymphatic vessels and organs
24.3 The lymphatic system becomes a crucial battleground during infection
The lymphatic system is a network of lymphatic vessels and organs
It returns tissue fluid to the circulatory system
It fights infections

10. LYMPHATIC VESSEL
Adenoid
Tonsil
VALVE
Right lymphatic duct, entering vein
Tissue cells
Lymph nodes
Interstitial fluid
Blood capillary
Thoracic duct, entering vein
Thoracic duct
Thymus
Appendix
LYMPHATIC CAPILLARY
Spleen
Masses of lymphocytes and
macrophages
Bone marrow
Lymphatic vessels
Figure 23.3

11. It will return it as lymph to the blood
This lymphatic vessel is taking up fluid from tissue spaces in the skin
It will return it as lymph to the blood
Lymph contains less oxygen and fewer nutrients than interstitial fluid
LYMPHATIC VESSEL
VALVE
Tissue cells
Interstitial fluid
Blood capillary
LYMPHATIC CAPILLARY
Figure 23.3B

12. Lymph nodes are key sites for fighting infection
They are packed with lymphocytes and macrophages
Masses of lymphocytes and
macrophages
Outer capsule of lymph node
Macrophages
Lymphocytes
Figure 23.3C, D

13. 24.4 The immune response counters specific invaders
SPECIFIC IMMUNITY
24.4 The immune response counters specific invaders
Our immune systems responds to foreign molecules called antigens
Infection or vaccination triggers active immunity
The immune system reacts to antigens and “remembers” an invader
We can temporarily acquire passive immunity

14. 24.5 Lymphocytes mount a dual defense
Two kinds of lymphocytes carry out the immune response
B cells secrete antibodies that attack antigens
T cells attack cells infected with pathogens
BONE MARROW
Stem cell
THYMUS
Via blood
Immature lymphocytes
Antigen receptors
T cell
B cell
CELL- MEDIATED IMMUNITY
HUMORAL IMMUNITY
Via blood
Lymph nodes, spleen, and other lymphatic organs
Final maturation of B and T cells in lymphatic organ
OTHER PARTS OF THE LYMPHATIC SYSTEM
Figure 24.5

15. 24.6 Antigens have specific regions where antibodies bind to them
Antigenic determinants are the molecules to which antibodies bind
Antibody A molecules
Antigen- binding sites
Antigenic determinants
Antigen
Antibody B molecule
Figure 24.6

16. 24.7 Clonal selection musters defensive forces against specific antigens
When an antigen enters the body, it activates only lymphocytes with complementary receptors
B and T cells multiply into clones of specialized effector cells that defend against the triggering antigen
This is called clonal selection

17. Antigen molecules
Variety of B cells in a lymph node
Antigen receptor (antibody on cell surface)
Cell growth
division, and
differentiation
Clone of many effector cells secreting antibodies
Endoplasmic reticulum
Antibody molecules
Figure 24.7

18. 24.8 The initial immune response results in a type of “memory”
In the primary immune response, clonal selection produces memory cells
These cells may confer lifelong immunity
Figure 24.8A

19. When memory cells are activated by subsequent exposure to an antigen, they mount a more rapid and massive secondary immune response
Unstimulated lymphocyte
First exposure to antigen
FIRST CLONE
Memory cells
Second exposure to antigen
Effector cells
SECOND CLONE
More memory cells
New effector cells
Figure 24.8B

20. 24.9 Overview: B cells are the main warriors of humoral immunity
Triggered by a specific antigen, a B cell differentiates into an effector cell
The effector cell is called a plasma cell
The plasma cell secretes antibodies

21. PRIMARY RESPONSE
(initial encounter
with antigen)
Antigen
Antigen receptor on a B cell
Antigen binding
to a B cell
Cell growth,
division, and
differentiation
Clone of cells
Memory B cell
Plasma cell
Antibody
molecules
Later
exposure
to same
antigen
SECONDARY RESPONSE
(can be years later)
Cell growth,
division, and further
differentiation
Larger clone
of cells
Plasma cell
Memory B cell
Antibody
molecules
Figure 24.9

22. 24.10 Antibodies are the weapons of humoral immunity
An antibody molecule
Figure 24.10A

23. An antibody molecule has antigen-binding sites specific to the antigenic determinants that elicited its secretion
Antigen-binding
sites
Light
chain
Heavy
chain
Figure 24.10B

24. 24.11 Antibodies mark antigens for elimination
Antibodies may
block harmful antigens on microbes
clump bacteria or viruses together
precipitate dissolved antigens
activate complement proteins

25. Binding of antibodies to antigens inactivates antigens by
Neutralization
(blocks viral binding sites;
coats bacterial toxins)
Agglutination
of microbes
Precipitation of
dissolved antigens
Activation
of complement
Complement
molecule
Bacteria
Virus
Antigen
molecules
Bacterium
Foreign cell
Hole
Enhances
Leads to
Phagocytosis
Cell lysis
Macrophage
Figure 24.11

26. producing monoclonal antibodies
Connection: Monoclonal antibodies are powerful tools in the lab and clinic
These molecules are produced by fusing B cells specific for a single antigenic determinant with easy-to-grow tumor cells
Antigen injected
into mouse
Tumor cells grown
in culture
B cells
(from spleen)
Tumor cells
Cells fused to
generate hybrid
cells
Single hybrid cell
grown in culture
Antibody
Hybrid cell culture,
producing monoclonal antibodies
Figure 24.12A

27. These cells are useful in medical diagnosis
Example: home pregnancy tests
They are also useful in the treatment of certain cancers
Figure 24.12B

28. 24.13 T cells mount the cell-mediated defense and aid humoral immunity
Helper T cells and cytotoxic T cells are the main effectors of cell-mediated immunity
Helper T cells also stimulate the humoral responses

29. Cell-mediated immunity
An antigen-presenting cell (APC) first displays a foreign antigen and one of the body’s own self proteins to a helper T cell
Microbe
Macrophage (will become APC) 1
Antigen from microbe (nonself molecule)
Self protein
Self protein
displaying
antigen
T cell receptor
Binding site for self protein 3 2
Helper
T cell 4
Binding site
for antigen
APC
Figure 24.13A

30. The helper T cell’s receptors recognize the self-nonself complexes on the APC
The interaction activates the helper T cells
The helper T cell can then activate cytotoxic T cells with the same receptors
Self protein
displaying
an antigen
Cell-mediated
immunity
(attack on
infected cells)
Cytotoxic
T cell
T cell
receptor
Interleukin-2
stimulates
cell division
Interleukin-2
activates
other T cells
and B cells
APC
Helper T cell
Humoral
immunity
(secretion of
antibodies by
plasma cells)
B cell
Interleukin-1
activates helper T cell
Figure 24.13B

31. Cytotoxic T cells bind to infected body cells and destroy them1
Cytotoxic T cell binds to infected cell 2
Perforin makes holes in infected cell’s membrane 3
Infected cell is destroyed
Hole forming
Foreign antigen
INFECTED CELL
Cytotoxic T cell
Perforin molecule
Figure 24.13C

32. 24.14 Cytotoxic T cells may help prevent cancer
Cytotoxic T cells may attack cancer cells
The surface molecules of cancer cells are altered by the disease
Figure 24.14

33. 24.15 The immune system depends on our molecular fingerprints
The immune system normally reacts only against nonself substances
It generally rejects transplanted organs
The cells of transplanted organs lack the recipient’s unique “fingerprint” of self proteins

34. DISORDERS OF THE IMMUNE SYSTEM
Connection: Malfunction or failure of the immune system causes disease
Autoimmune diseases
The system turns against the body’s own molecules
Immunodeficiency diseases
Immune components are lacking, and infections recur
Physical and emotional stress may weaken the immune system

35. Allergies are abnormal sensitivities to allergens in the surroundings
Connection: Allergies are overreactions to certain environmental antigens
Allergies are abnormal sensitivities to allergens in the surroundings
B cell
(plasma cell)
Histamine
Mast
cell
Antigenic
determinant
Antibodies
attach to
mast cell
Allergen
(pollen grain)
B cells make
antibodies
Allergen binds to
antibodies on
mast cell
Histamine is
released, causing
allergy symptoms
SENSITIZATION: Initial exposure to allergen
LATER EXPOSURE TO SAME ALLERGEN
Figure 24.17

36. 24.18 Connection: AIDS leaves the body defenseless
The AIDS virus attacks helper T Cells
This cripples both cell-mediated and humoral immunity
So far, AIDS is incurable
Drugs and vaccines offer hope for the future
Practicing safer sex could save many lives