1. CHAPTER 24 The Immune System
Modules – 24.17

2. 24.10 Antibodies are the weapons of humoral immunity
An antibody molecule
Figure 24.10A

3. 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

4. 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

5. 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

6. 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

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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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