1. Chapter 24
The Immune System

2. ADAPTIVE IMMUNITY
Responsible for specific response and immune system memory
© 2012 Pearson Education, Inc. 2

3. 24.5 Lymphocytes mount a dual defense
B cells
participate in the humoral immune response and
secrete antibodies into the blood and lymph
Attack pathogens OUTSIDE body cells!!!!
T cells
participate in the cell-mediated immune response,
attack cells infected with bacteria or viruses, and
Help bridge B-cell and Innate immune responses.
Student Misconceptions and Concerns
1. For students with limited science backgrounds, this section of the chapter can be particularly difficult; for some, it is the most challenging part of the textbook. Students must have a solid knowledge of the properties of different cells and their interactions, and understand that repeated exposure to antigens generates new interactions. The challenge is similar to explaining a new sport to someone unfamiliar to the game. (Imagine explaining the rules and strategies of football or poker to someone who had never heard of them.) Instructors might consider slowing their pace and using learning aids such as reference lists of cell types and their functions, or diagrams that remind students of these cellular interactions.
2. Having students read relevant material before it is addressed in lecture is one of the best ways to improve student comprehension. Before lecturing on a topic, identify specific textbook modules that should be read before you address them in class. Reading before lecture can lay a foundation that makes the lecture much more meaningful. However, it helps in other ways, too. As students listen in lecture, they know if definitions in lecture are included in the book, and students are already aware of which figures outline certain processes.
Teaching Tips
Many analogies can be developed relating to the cells and molecules involved in the immune response. In Module 24.5, the authors note that lymphocytes, which can respond to any antigen, resemble a standing army of soldiers in which each soldier is able to recognize a unique form of the enemy.
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4. Each receptor can specifically bind to a unique antigen
Key Point to Remember:
Each B and T cell displays unique set of antigen receptors on cell surface
Each receptor can specifically bind to a unique antigen
Stem cell
Bone marrow
Via blood
Immature lymphocytes
Thymus
Antigen receptors
Via blood
B cell
T cell
Final maturation of B and T cells in a lymphatic organ
Figure 24.5A The development of B cells and T cells
Lymph nodes, spleen, and other lymphatic organs
Humoral immune response
Cell-mediated immune response 4

5. Development of Immune System Memory by CLONAL SELECTION
Legal Disclaimer:
Clonal selection occurs in a similar manner for
T cell-mediated immune memory
(the following events are fictional - any resemblance to
Historical characters is just coincidence - no B cells or
Pathogens were actually harmed in the making of this animation.
Student Misconceptions and Concerns
1. For students with limited science backgrounds, this section of the chapter can be particularly difficult; for some, it is the most challenging part of the textbook. Students must have a solid knowledge of the properties of different cells and their interactions, and understand that repeated exposure to antigens generates new interactions. The challenge is similar to explaining a new sport to someone unfamiliar to the game. (Imagine explaining the rules and strategies of football or poker to someone who had never heard of them.) Instructors might consider slowing their pace and using learning aids such as reference lists of cell types and their functions, or diagrams that remind students of these cellular interactions.
2. Having students read relevant material before it is addressed in lecture is one of the best ways to improve student comprehension. Before lecturing on a topic, identify specific textbook modules that should be read before you address them in class. Reading before lecture can lay a foundation that makes the lecture much more meaningful. However, it helps in other ways, too. As students listen in lecture, they know if definitions in lecture are included in the book, and students are already aware of which figures outline certain processes.
Teaching Tips
Our own learning experiences provide an analogy to the greater swiftness and intensity of a secondary immune response. When first presented with a problem, we may struggle to determine how best to respond. However, with that first experience behind us, we expect to respond more quickly and effectively when we meet that challenge again. Although in each circumstance we benefit from a certain type of memory (experiential in one case, chemical in the other) their mechanisms are quite different. Consider noting these similarities and differences in your class discussion of primary and secondary immune responses.
Animation: Role of B Cells
© 2012 Pearson Education, Inc. 5

6. Every B cell displays unique antigen receptor on surface
CLONAL SELECTION
Primary immune response
Antigen receptor on the cell surface
B cells with different antigen receptors 1
Every B cell displays unique antigen receptor on surface
Figure 24.7A_s1 Clonal selection of B cells: primary response (part 1, step 1) 6

7. Antigen only binds to B cell with complementary receptor
CLONAL SELECTION
Primary immune response 2
Antigen molecules
Antigen receptor on the cell surface
B cells with different antigen receptors 1
Antigen only binds to B cell with complementary receptor
Figure 24.7A_s2 Clonal selection of B cells: primary response (part 1, step 2) 7

8. The selected B cell now divides rapidly!!!
CLONAL SELECTION
Primary immune response 2
Antigen molecules
Antigen receptor on the cell surface
B cells with different antigen receptors 1 3
First exposure to the antigen
I WON THE
ANTIGEN
LOTTERY!!
Figure 24.7A_s3 Clonal selection of B cells: primary response (part 1, step 3)
The selected B cell now divides rapidly!!! 8

9. Plasma cells - secrete antibodies Memory cells
Figure 24.7A_s4
Primary immune response 2
Antigen molecules
Antigen receptor on the cell surface
B cells with different antigen receptors 1
We’ll hang out
And wait for the
next invasion
We’ll mark the
Pathogen for
Elimination!! 3
First exposure to the antigen
Antibody molecules
Figure 24.7A_s4 Clonal selection of B cells: primary response (part 1, step 4) 4 5
Plasma cells - secrete antibodies
Memory cells 9

10. Secondary immune response
Figure 24.7A_s5
Secondary immune response
Alright boys, the pathogen is
Back!! Looks like we’re in
Charge of the second offensive -
Get ready to divide!!
Antigen molecules
Second exposure to the same antigen
Figure 24.7A_s5 Clonal selection of B cells: secondary response (part 2, step 1)
Memory cells 10

11. Plasma cells Memory cells
Secondary immune response
Looks like we are off to fight
This pathogen again!
But now we can respond
Faster with a larger army - those
Bugs won’t know what hit them!
Antibody molecules
Plasma cells
Memory cells
divide
Figure 24.7A_s6 Clonal selection of B cells: secondary response (part 2, step 2)
Memory cells
Memory cells 11

12. 2nd response occurs quicker with greater magnitude!!
Second exposure to antigen X, first exposure to antigen Y
Secondary immune response to antigen X
First exposure to antigen X
Antibody concentration
Primary immune response to antigen X
Primary immune response to antigen Y
Figure 24.7B The two phases of the adaptive immune response
Antibodies to X
Antibodies to Y 7 14 21 28 35 42 49 56
Time (days) 12

13. But what IS an Antibody????? Protein made of 4 separate subunits
Protein made of 4 separate subunits
Sits on surface of B cells until B cell stimulated to release antibodies into body fluids
Student Misconceptions and Concerns
1. For students with limited science backgrounds, this section of the chapter can be particularly difficult; for some, it is the most challenging part of the textbook. Students must have a solid knowledge of the properties of different cells and their interactions, and understand that repeated exposure to antigens generates new interactions. The challenge is similar to explaining a new sport to someone unfamiliar to the game. (Imagine explaining the rules and strategies of football or poker to someone who had never heard of them.) Instructors might consider slowing their pace and using learning aids such as reference lists of cell types and their functions, or diagrams that remind students of these cellular interactions.
2. Having students read relevant material before it is addressed in lecture is one of the best ways to improve student comprehension. Before lecturing on a topic, identify specific textbook modules that should be read before you address them in class. Reading before lecture can lay a foundation that makes the lecture much more meaningful. However, it helps in other ways, too. As students listen in lecture, they know if definitions in lecture are included in the book, and students are already aware of which figures outline certain processes.
Teaching Tips
Challenge your class to explain the adaptive advantages of antibodies’ Y-shaped structure. Why aren’t antibodies just made up of a single heavy and a single light chain? (Biologists have theorized that the Y shape permits the bonding together of two antigens or antigen-presenting surfaces, allowing a chain reaction or form of clumping.)
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14. Light chain Heavy chain Figure 24.8A
Figure 24.8A A computer graphic of an antibody molecule 14

15. Antigen-binding sites
Figure 24.8B
Antigen
Antigen-binding sites V V V V C C
Light chain
Antigen-binding site VARIES between each unique antibody C C
Figure 24.8B Antibody structure and the binding of an antigen-binding site to its complementary antigen (enlargement)
Heavy chain
The CONSTANT region defines Ab class and effector action
V = variable
C = constant 15

16. Antibodies mark antigens for elimination
Binding of antibodies to antigens inactivates antigens by
Neutralization (blocks viral binding sites; coats bacteria)
Agglutination of microbes
Precipitation of dissolved antigens
Activation of the complement system
Complement molecule
Bacteria
Virus
Antigen molecules
Bacterium
Foreign cell
Hole
Enhances
Leads to
Figure 24.9 Effector mechanisms of the humoral immune response
Phagocytosis
Cell lysis
Macrophage
Animation: Antibodies 16

17. T cell mediated immune function
T-Cells Detect presence of foreign antigens on SURFACE of virally or bacterially infected body cells
2 types of T cells:
Helper T cells -- stimulate B-cell and T-cell mediated immune responses
Cytotoxic T cells
DESTROY infected cells as marked by Helper T cells
Student Misconceptions and Concerns
1. For students with limited science backgrounds, this section of the chapter can be particularly difficult; for some, it is the most challenging part of the textbook. Students must have a solid knowledge of the properties of different cells and their interactions, and understand that repeated exposure to antigens generates new interactions. The challenge is similar to explaining a new sport to someone unfamiliar to the game. (Imagine explaining the rules and strategies of football or poker to someone who had never heard of them.) Instructors might consider slowing their pace and using learning aids such as reference lists of cell types and their functions, or diagrams that remind students of these cellular interactions.
2. Having students read relevant material before it is addressed in lecture is one of the best ways to improve student comprehension. Before lecturing on a topic, identify specific textbook modules that should be read before you address them in class. Reading before lecture can lay a foundation that makes the lecture much more meaningful. However, it helps in other ways, too. As students listen in lecture, they know if definitions in lecture are included in the book, and students are already aware of which figures outline certain processes.
Teaching Tips
1. The authors note that the recognition by a helper T cell of a self protein and a foreign antigen in combination is like the two-key system used by banks to access safe-deposit boxes.
2. Your students might find the descriptions in Modules and to be particularly confusing, as the interactions of many cell types are described. Figures and help to simplify the details of these interactions.
Animation: Helper T Cells
Animation: Cytotoxic T Cells
Video: T Cell Receptors
© 2012 Pearson Education, Inc. 17

18. The humoral immune response:
Figure 24.UN01
The humoral immune response:
makes
which bind to
B cell
Antibodies
Antigens in body fluid
The cell-mediated immune response:
Infected body cell
Figure 24.UN01 Reviewing the Concepts, 24.5
T cell
Self-nonself complex 18

19. Infected body cells will display antigens of pathogen on cell surface
Humoral immune response (secretion of antibodies by plasma cells)
Phagocytic cell (yellow) engulfing a foreign cell
Self-nonself complex
B cell
Interleukin-2 stimulates cell division
T cell receptor
Microbe
Macrophage 3 5 6
Interleukin-2 activates B cells and other T cells 1 2
Helper T cell 4 7
Self protein
Cell-mediated immune response (attack on infected cells)
Binding site for the self protein
Antigen-presenting cell
Cytotoxic T cell
Antigen from the microbe (nonself molecule)
Figure The activation of a helper T cell and its roles in immunity
Binding site for the antigen
Helper T cells are trained to recognize foreign antigens and alert B cells and Cytotoxic T cells 19

20. How are B and T cells trained to recognize ‘self’ vs
How are B and T cells trained to recognize ‘self’ vs. ‘non-self’ antigens????
Each of us display a unique protein and carbohydrate ‘fingerprint’ on the surface of our cells
This fingerprint is referred to as the MHC protein complex
During development, B and T cells are exposed to MHC proteins
Any B or T cells that have antigen receptors that can bind to ‘self’ antigens are DESTROYED!!
This is called CLONAL DELETION.
Student Misconceptions and Concerns
1. For students with limited science backgrounds, this section of the chapter can be particularly difficult; for some, it is the most challenging part of the textbook. Students must have a solid knowledge of the properties of different cells and their interactions, and understand that repeated exposure to antigens generates new interactions. The challenge is similar to explaining a new sport to someone unfamiliar to the game. (Imagine explaining the rules and strategies of football or poker to someone who had never heard of them.) Instructors might consider slowing their pace and using learning aids such as reference lists of cell types and their functions, or diagrams that remind students of these cellular interactions.
2. Having students read relevant material before it is addressed in lecture is one of the best ways to improve student comprehension. Before lecturing on a topic, identify specific textbook modules that should be read before you address them in class. Reading before lecture can lay a foundation that makes the lecture much more meaningful. However, it helps in other ways, too. As students listen in lecture, they know if definitions in lecture are included in the book, and students are already aware of which figures outline certain processes.
Teaching Tips
Students may enter your course knowing that the best types of tissue transplants are from a closely matched donor. However, what does it mean to have a tissue “match”? Few students can explain the specific reasons behind the need for tissue matching, or how such matching is done. Challenge your students to explain why we try to ensure a match between the tissues of a donor and a recipient. By posing such general questions, instructors can raise interest in the specific details of the answers.
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