1. Immune System
Chapter 24

2. An AIDS Uproar Acquired immune deficiency syndrome (AIDS)
An AIDS Uproar
Acquired immune deficiency syndrome (AIDS)
Is epidemic throughout much of the world
Thousands of people are infected every day

3. HIV, the virus that causes AIDS, attacks the immune system
And eventually destroys the body’s ability to fight infection

4. INNATE DEFENSES AGAINST INFECTION
24.1 Innate defenses against infection include the skin and mucous membranes, phagocytic cells, and antimicrobial proteins
Innate immunity
Is present and effective long before exposure to pathogens

5. Microbes that breach the body’s external defenses
Microbes that breach the body’s external defenses
Are engulfed and destroyed by macrophages
Colorized SEM 3,800
Bacteria
Figure 24.1A

6. Interferons are proteins produced by virus-infected cells
That help other cells resist viruses 1
Viral nucleic acid
Antiviral proteins block viral reproduction 2
Interferon genes turned on
New viruses
DNA
mRNA 3
Interferon molecules
Interferon stimulates cell to turn on genes for antiviral proteins 5 4
Host cell 1
Makes interferon; is killed by virus
Host cell 2
Protected against virus by interferon from cell 1
Figure 24.1B

7. 24.2 The inflammatory response mobilizes nonspecific defense forces
24.2 The inflammatory response mobilizes nonspecific defense forces
Tissue damage triggers the inflammatory response
Pin
Skin surface
Swelling
Bacteria
Phagocytes and fluid move into area
Phagocytes
Chemical signals
White blood cell
Blood vessel 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 and limit further infection

9. 24.3 The lymphatic system becomes a crucial battleground during infection
The lymphatic system
Is a network of lymphatic vessels and organs
Adenoid
Tonsil
Lymph nodes
Right lymphatic duct, entering vein
Thymus
Appendix
Thoracic duct
Bone marrow
Lymphatic vessels
Spleen
Thoracic duct, entering vein
Lymph node
Masses of lymphocytes and macrophages
Valve
Lymphatic vessel
Blood capillary
Tissue cells
Interstitial fluid
Lymphatic capillary
Figure 24.3

10. The vessels collect fluid from body tissues
And return it as lymph to the blood
Lymph organs such as the spleen and lymph nodes
Are packed with white blood cells that fight infections

11. ACQUIRED IMMUNITY 24.4 The immune response counters specific invaders
24.4 The immune response counters specific invaders
Our immune system
Responds to foreign molecules called antigens
The immune system reacts to antigens
And “remembers” an invader

12. We can temporarily acquire passive immunity
We can temporarily acquire passive immunity
By receiving “premade” antibodies
Infection or vaccination
Triggers active immunity
Figure 24.4

13. Cell-mediated immunity
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
Thymus
Stem cell
Immature lymphocyte
B cell
Humoral immunity
Via
blood
Antigen
receptors
T cell
Cell-mediated immunity
Lymph nodes, spleen, and other lymphatic organs
Final maturation of B and T cells in lymphatic organ
Other parts of the lymphatic system
Figure 24.5A

14. Wait in the lymphatic system, where they may respond to invaders
Millions of kinds of B cells and T cells, each with different membrane receptors
Wait in the lymphatic system, where they may respond to invaders
Colorized TEM 4,500
Figure 24.5B

15. Antigenic determinants
24.6 Antigens have specific regions where antibodies bind to them
Antigenic determinants
Are the specific regions on an antigen to which antibodies bind
Antibody A molecules
Antigen-binding sites
Antigen molecule
Antigenic determinants
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 a small subset of lymphocytes with complementary receptors

17. The selected lymphocyte cells multiply into clones of short-lived effector cells
Specialized for defending against the antigen that triggered the response

18. The Steps of Clonal Selection
The Steps of Clonal Selection
In the primary immune response, clonal selection
Produces effector cells and memory cells that may confer lifelong immunity
In the secondary immune response
Memory cells are activated by a second exposure to the same antigen, which initiates a faster and more massive response

19. The primary and secondary immune responses
The primary and secondary immune responses
Primary immune response 2 1
Antigen receptor (antibody on cell surface)
Antigen molecules
B cells with different response
First exposure antigen 3
Cell activation: growth, division, and differentiation
Antibody molecules 4 5 5
Endoplasmic reticulum
Plasma (effector) cells secreting antibodies
Clone of memory cells
Antigen molecules 6
Second exposure to same antigen
Secondary immune response
Antibody molecules
Endoplasmic reticulum
Figure 24.7A
Plasma (effector) cells secreting antibodies
Clone of memory cells

20. Primary vs. Secondary Immune Response
Primary vs. Secondary Immune Response
The primary immune response
Is slower than the secondary immune response
Second exposure to antigen X, first exposure to antigen Y
First exposure to antigen X
Primary immune response to antigen X
Primary immune response to antigen Y
Antibodies to Y
Antibodies to X
Antibody concentration
Time (days)
Secondary immune response to antigen X
Figure 24.7B

21. 24.8 Antibodies are the weapons of humoral immunity
24.8 Antibodies are the weapons of humoral immunity
Antibody molecules
Are secreted by plasma (effector) B cells
Figure 24.8A

22. Antigen-binding sites
An antibody molecule
Has antigen-binding sites specific to the antigenic determinants that elicited its secretion
Light chain
Heavy chain C V
Antigen-binding sites
Figure 24.8B

23. 24.9 Antibodies mark antigens for elimination
24.9 Antibodies mark antigens for elimination
Antibodies promote antigen elimination
Through several mechanisms
Binding of antibodies to antigens inactivates antigens by
Neutralization
(blocks viral binding sites; coats bacteria)
Agglutination
of microbes
Precipitation of dissolved antigens
Activation of
Complement system
Cell Iysis
Phagocytosis
Virus
Bacterium
Bacteria
Antigen molecules
Complement molecule
Foreign cell
Hole
Macrophage
Enhances
Leads to
Figure 24.9

24. Hybrid cell culture, producing monoclonal antibodies
CONNECTION
24.10 Monoclonal antibodies are powerful tools in the lab and clinic
Monoclonal antibodies
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 24.10A

25. These molecules
Are useful in research, diagnosis, and treatment of certain cancers

26. 24.11 Helper T cells stimulate humoral and cell-mediated immunity
24.11 Helper T cells stimulate humoral and cell-mediated immunity
Helper T cells and cytotoxic T cells
Are the main effectors of cell-mediated immunity
Helper T cells
Also stimulate the humoral responses

27. In cell-mediated immunity, an antigen-presenting cell
Displays a foreign antigen and one of the body’s own self proteins to a helper T cell

28. The helper T cell’s receptors
Recognize the self-nonself complexes and the interaction activates the helper T cells
The helper T cell
Can then activate cytotoxic T cells and B cells

29. Antigen from microbe (nonself molecule)
The activation of a helper T cell and its roles in immunity
Humoral
Immunity
(secretion of antibodies by plasma cells)
Self-nonself
complex
B cell
T cell receptor
Interleukin-2
stimulates
cell division
Microbe
Macrophage
Interleukin-2
activates
other B cells and T cells 3 5 6 1 2
Helper
T cell 4 7
Self protein
Cell-mediated immunity (attack on infected cells)
Cytotoxic T cell
Antigen-presenting cell
Interleukin-1 stimulates helper T cell
Binding site for antigen
Binding site for self protein
Antigen from microbe (nonself molecule)
Figure 24.11

30. CONNECTION
24.12 HIV destroys helper T cells, compromising the body’s defenses
The AIDS virus attacks helper T Cells
Opening the way for opportunistic infection
Colorized EM 7,000
Figure 24.12

31. 24.13 Cytotoxic T cells destroy infected body cells
24.13 Cytotoxic T cells destroy infected body cells
Cytotoxic T cells
Bind to infected body cells and destroy them
1 Cytotoxic T cell binds to infected cell
2 Perforin makes holes in infected cell’s membrane and enzyme enters
3 Infected cell is destroyed
Self-nonself complex
Hole forming
Foreign antigen
Infecte cell
Perforin molecule
Cytotoxic T cell
Enzyme that can promote apoptosis
Figure 24.13

32. 24.14 Cytotoxic T cells may help prevent cancer
24.14 Cytotoxic T cells may help prevent cancer
Cytotoxic T cells may attack cancer cells
Which have abnormal surface molecules
Colorized SEM 4,370
Figure 24.14

33. 24.15 The immune system depends on our molecular fingerprints
24.15 The immune system depends on our molecular fingerprints
The immune system
Normally reacts only against nonself substances, not against self
May reject transplanted organs because these cells lack the unique “fingerprint” of the recipient’s self proteins

34. DISORDERS OF THE IMMUNE SYSTEM CONNECTION
24.16 Malfunction or failure of the immune system causes disease
In autoimmune diseases
The system turns against the body’s own molecules
In immunodeficiency diseases
Immune components are lacking, and frequent infections recur
Physical and emotional stress
May weaken the immune system

35. 24.17 Allergies are overreactions to certain environmental antigens
CONNECTION
24.17 Allergies are overreactions to certain environmental antigens
Allergies
Are abnormal sensitivities to antigens (allergens) in the surroundings

36. The two stages of an allergic reaction
The two stages of an allergic reaction
B cell (plasma cell)
Mast cell
Antigenic determinant
Histamine
1 Allergen (pollen grain) enters blood stream
2 B cells make antibodies
3 Antibodies attach to mast cell
4 Allergen binds to antibodies on mast cell
5 Histamine is released, causing allergy symptoms
Sensitization: Initial exposure to allergen
Later exposure to same allergen
3 Antibodies attach to mast cell
Figure 24.17