1. How do immune cells of animals recognize foreign cells?
Fig 43.1 How do immune cells of animals recognize foreign cells?
For the Cell Biology Video Leukocyte Adhesion and Rolling, go to Animation and Video Files.
1.5 µm

2. Animal Immunity INNATE IMMUNITY Barrier defenses: Internal defenses:
Pathogens
(microorganisms
and viruses)
INNATE IMMUNITY
Barrier defenses:
Skin
Mucous membranes
Secretions •
Recognition of traits
shared by broad ranges
of pathogens, using a
small set of receptors
Non-specific
Internal defenses:
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells •
Rapid response
Figure 43.2 Overview of animal immunity
ACQUIRED IMMUNITY
Humoral response:
Antibodies defend against
infection in body fluids. •
Recognition of traits
specific to particular
pathogens, using a vast
array of receptors
Cell-mediated response:
Cytotoxic lymphocytes defend
against infection in body cells. •
Slower response

3. Phagocytosis Vacuole Lysosome Microbes PHAGOCYTIC CELL Containing
hydrolytic
enzymes
Figure 43.3 Phagocytosis

4. TLR signaling EXTRACELLULAR FLUID Lipopolysaccharide Helper protein
Flagellin
TLR4
WHITE
BLOOD
CELL
TLR5
VESICLE
TLR9
CpG DNA
Figure 43.6 TLR signaling
Inflammatory
responses
TLR3
ds RNA

5. Lymphatic System Interstitial fluid Adenoid Tonsil Blood capillary
nodes
Spleen
Tissue
cells
Lymphatic
vessel
Peyer’s patches
(small intestine)
Appendix
Figure 43.7 The human lymphatic system
Lymphatic
vessels
Lymph
node
Masses of
defensive cells

6. 3. 1. 2. Major events in a local Inflammatory Response Pathogen
Splinter
Chemical
signals
Macrophage
Fluid
Mast cell
Capillary
Phagocytosis
Figure 43.8 Major events in a local inflammatory response
For the Cell Biology Video Chemotaxis of a Neutrophil, go to Animation and Video Files.
Red blood cells
Phagocytic cell

7. Antigen receptors on lymphocytes
binding
site
Antigen-
binding site
Antigen-
binding
site V
Disulfide
bridge V V V
Variable
regions C V V C
Constant
regions C C C C
Light
chain
Transmembrane
region
Plasma
membrane
Heavy chains
 chain
 chain
Figure 43.9 Antigen receptors on lymphocytes
Disulfide bridge
B cell
Cytoplasm of B cell
Cytoplasm of T cell
T cell
B cell receptor
T cell receptor

8. Epitopes = antigen determinants
binding
sites
Epitopes
(antigenic
determinants)
Antigen-binding sites
Antibody A
Antigen V V
Antibody C V V C C C C
Figure Epitopes (antigenic determinants)
Antibody B

9. Antigen Presentation by an MHC molecule
Top view: binding surface
exposed to antigen receptors
Antigen
Class I MHC
molecule
Antigen
Figure Antigen presentation by an MHC molecule
Plasma
membrane of
infected cell

10. Interaction of T cells with Antigen-Presenting Cells
Infected cell
Microbe
Antigen-
presenting
cell 1
Antigen
associates
with MHC
molecule
Antigen
fragment
Antigen
fragment 1 1
Class I MHC
molecule
Class II MHC
molecule 2 2
T cell
receptor
T cell
receptor 2
T cell
recognizes
combination
Figure The interaction of T cells with antigen-presenting cells
(a)
Cytotoxic T cell
(b)
Helper T cell

11. Clonal Selection of B cells
Antigen molecules
B cells that
differ in
antigen
specificity
Antigen
receptor
Figure Clonal selection of B cells
Antibody
molecules
Clone of memory cells
Clone of plasma cells = effectors

12. Antibody concentration
Primary immune response
to antigen A produces
antibodies to A.
Secondary immune response to
antigen A produces antibodies to A.
Primary immune response to antigen
B produces antibodies to B.
104
103
Antibody concentration
(arbitrary units)
Antibodies
to A
102
Antibodies
to B
101
Figure The specificity of immunological memory
100 7 14 21 28 35 42 49 56
Exposure
to antigen A
Exposure to
antigens A and B
Time (days)

13. Acquired Immune Response
Humoral (antibody-mediated) immune response
Cell-mediated immune response
Key
Antigen (1st exposure) +
Stimulates
Gives rise to
Engulfed by
Antigen-
presenting cell + + +
B cell
Helper T cell
Cytotoxic T cell + +
Memory
Helper T cells + + +
Figure An overview of the acquired immune response
Antigen (2nd exposure) +
Memory
Cytotoxic T cells
Active
Cytotoxic T cells
Plasma cells
Memory B cells
Secreted
antibodies
Defend against extracellular pathogens by binding to antigens,
thereby neutralizing pathogens or making them better targets
for phagocytes and complement proteins.
Defend against intracellular pathogens
and cancer by binding to and lysing the
infected cells or cancer cells.

14. Acquired Immune Response Humoral (antibody-mediated) immune response
Key
Antigen (1st exposure) +
Stimulates
Gives rise to
Engulfed by
Antigen-
presenting cell + +
B cell
Helper T cell +
Memory
Helper T cells + +
Figure An overview of the acquired immune response
Antigen (2nd exposure)
Plasma cells
Memory
B cells +
Secreted
antibodies
Defend against extracellular pathogens

15. Acquired Immune Response Cell-mediated immune response
Antigen (1st exposure)
Key +
Stimulates
Gives rise to
Engulfed by
Antigen-
presenting cell + +
Helper T cell
Cytotoxic T cell +
Memory
Helper T cells
Figure An overview of the acquired immune response + +
Antigen (2nd exposure)
Active
Cytotoxic T cells +
Memory
Cytotoxic T cells
Defend against intracellular pathogens

16. The central role of helper T cells in humoral and cell-mediated immune responses
Antigen-
presenting
cell
Peptide antigen
Bacterium
Class II MHC molecule
CD4
TCR (T cell receptor)
Helper T cell
Cytokines
Positive Feedback … +
Humoral
immunity
= secretion of
antibodies by
plasma cells. +
Cell-mediated
immunity
= attack on
infected cells.
Figure The central role of helper T cells in humoral and cell-mediated immune responses + +
B cell
Cytotoxic T cell

17. 3. lysis 1. 2. The killing action of cytotoxic T cells
Released cytotoxic T cell
Cytotoxic T cell
Perforin
Granzymes
CD8
TCR
Dying target cell
Class I MHC
molecule
Pore
Figure The killing action of cytotoxic T cells
For the Discovery Video Fighting Cancer, go to Animation and Video Files.
Target
cell
Peptide
antigen

18. B cell activation in the humoral immune response
Antigen-presenting cell
Bacterium
Peptide
antigen
B cell
Class II MHC
molecule
Secreted
antibody
molecules +
Clone of plasma cells
TCR
CD4
Cytokines
Endoplasmic
reticulum of
plasma cell
Activated
helper T cell
Helper T cell
Clone of memory
B cells
Figure B cell activation in the humoral immune response
2 µm

19. The five antibody, or immunoglobulin (Ig), classes
Class of Immuno-
globulin (Antibody)
Distribution
Function
IgM
(pentamer)
First Ig class
produced after
initial exposure to
antigen; then its
concentration in
the blood declines
Promotes neutraliza-
tion and cross-
linking of antigens;
very effective in
complement system
activation
J chain
IgG
(monomer)
Most abundant Ig
class in blood;
also present in
tissue fluids
Promotes opsoniza-
tion, neutralization,
and cross-linking of
antigens; less effec-
tive in activation of
complement system
than IgM
Only Ig class that
crosses placenta,
thus conferring
passive immunity
on fetus
IgA
(dimer)
Present in
secretions such
as tears, saliva,
mucus, and
breast milk
Provides localized
defense of mucous
membranes by
cross-linking and
neutralization of
antigens
J chain
Presence in breast
milk confers
passive immunity
on nursing infant
Secretory
component
Figure The five antibody, or immunoglobulin (Ig), classes
IgE
(monomer)
Present in blood
at low concen-
trations
Triggers release from
mast cells and
basophils of hista-
mine and other
chemicals that cause
allergic reactions
IgD
(monomer)
Present primarily
on surface of
B cells that have
not been exposed
to antigens
Acts as antigen
receptor in the
antigen-stimulated
proliferation and
differentiation of
B cells (clonal
selection)
Trans-
membrane
region

20. Antibody-mediated mechanisms of antigen disposal
Activation of complement system
and pore formation
Viral neutralization
Opsonization
Bacterium
Complement proteins
Virus
Formation of
membrane
attack complex
Flow of water
and ions
Macrophage
Pore
Figure Antibody-mediated mechanisms of antigen disposal
Foreign
cell

21. Passive immunization of an infant occurs during breast-feeding
Figure Passive immunization of an infant occurs during breast-feeding
For the Discovery Video Vaccines, go to Animation and Video Files.

22. Mast cells, IgE, and the allergic response
Histamine
Allergen
Granule
Figure Mast cells, IgE, and the allergic response
Mast cell

23. X-ray of a hand deformed by rheumatoid arthritis
Figure X-ray of a hand deformed by rheumatoid arthritis

24. Helper T cell concentration
The progress of an untreated HIV infection
Latency
AIDS
Relative antibody
concentration
800
Relative HIV
concentration
600
Helper T cell concentration
in blood (cells/mm3)
Helper T cell
concentration
400
Figure The progress of an untreated HIV infection
200 1 2 3 4 5 6 7 8 9 10
Years after untreated infection

25. Review Stem cell Cell division and gene rearrangement Elimination of
self-reactive
B cells
Antigen
Clonal selection
Formation of activated cell populations
Antibody
Memory cells
Effector B cells
Microbe
Receptors bind to antigens

26. You should now be able to:
Distinguish between innate and acquired immunity.
Name and describe four types of phagocytic cells.
Describe the inflammation response.

27. Distinguish between the following pairs of terms: antigens and antibodies; antigen and epitope; B lymphocytes and T lymphocytes; antibodies and B cell receptors; primary and secondary immune responses; humoral and cell-mediated response; active and passive immunity.
Explain how B lymphocytes and T lymphocytes recognize specific antigens.
Explain why the antigen receptors of lymphocytes are tested for self-reactivity.

28. Describe clonal selection and distinguish between effector cells and memory cells.
Describe the cellular basis for immunological memory.
Explain how a single antigen can provoke a robust humoral response.
Compare the processes of neutralization and opsonization.

29. Describe the role of MHC in the rejection of tissue transplants.
Describe an allergic reaction, including the roles of IgE, mast cells, and histamine.
Describe some of the mechanisms that pathogens have evolved to thwart the immune response of their hosts.
List strategies that can reduce the risk of HIV transmission.