1. Chapter 43
The Immune System

2. Overview: Reconnaissance, Recognition, and Response
Barriers help an animal to defend itself from the many dangerous pathogens it may encounter
The immune system recognizes foreign bodies and responds with the production of immune cells and proteins
Two major kinds of defense have evolved:
innate immunity
acquired immunity

3. Fig. 43-1
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

4. Innate immunity is present before any exposure to pathogens and is effective from the time of birth
It involves nonspecific responses to pathogens
Innate immunity consists of
external barriers
internal cellular
chemical defenses

5. Acquired immunity, or adaptive immunity:
develops after exposure to agents such as microbes, toxins, or other foreign substances
It involves a very specific response to pathogens

6. Pathogens (microorganisms and viruses)
Fig. 43-2
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
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

7. In innate immunity, recognition and response rely on shared traits of pathogens
Both invertebrates and vertebrates depend on
Innate immunity to fight infection
Vertebrates also develop:
acquired immune defenses

8. Innate Immunity of Invertebrates
In insects:
An exoskeleton made of chitin forms the first barrier to pathogens
The digestive system is protected by:
low pH
lysozyme (an enzyme digests microbial cell walls)
Hemocytes:
circulate within hemolymph
carry out phagocytosis (ingestion & digestion of foreign substances including bacteria)
Secrete antimicrobial peptides (disrupting the plasma membranes of bacteria)

9. Microbes PHAGOCYTIC CELL Vacuole Lysosome containing enzymes Fig. 43-3
Figure 43.3 Phagocytosis

10. Fig. 43-4
Figure 43.4 An inducible innate immune response

11. The immune system recognizes bacteria and fungi by:
Structures on their cell walls
An immune response varies with:
The class of pathogen encountered

12. Innate Immunity of Vertebrates
The immune system of mammals:
is the best understood of the vertebrates
Innate defenses include:
Barrier defenses
Phagocytosis
Antimicrobial peptides
Additional defenses are unique to vertebrates:
The inflammatory response, and
Natural killer cells

13. Barrier Defenses
Barrier defenses include:
The skin & mucous membranes
Mucus traps & allows removal of microbes
Many body fluids including:
saliva, mucus, & tears are hostile to microbes
The low pH of(prevents growth of microbes) :
The skin
The digestive system

14. Cellular Innate Defenses
White blood cells (leukocytes):
Engulf pathogens in the body
Groups of pathogens are recognized by:
TLR, Toll-like receptors

15. Fuses with a lysosome & destroy the microbe
A white blood cell:
Engulfs a microbe,
Fuses with a lysosome & destroy the microbe
There are different types of phagocytic cells:
Neutrophils:
engulf and destroy microbes
Macrophages:
are part of the lymphatic system; found throughout the body
Eosinophils:
discharge destructive enzymes
Dendritic cells:
stimulate development of acquired immunity

16. Interstitial fluid Adenoid Tonsil Blood capillary Lymph nodes Spleen
Fig. 43-7
Interstitial fluid
Adenoid
Tonsil
Blood
capillary
Lymph
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

17. Antimicrobial Peptides and Proteins
Function in innate defense by:
Attacking microbes directly or impeding their reproduction
Interferon:
Proteins provide innate defense
Work against viruses
Help activate macrophages
Complement system;
Made up of about 30 proteins
causes lysis of invading cells
Helps trigger inflammation

18. Inflammatory Responses
Following an injury:
mast cells release histamine
Histamine promotes vasodilation
This is part of the inflammatory response
Changes cause ncrease local blood supply
More phagocytes & antimicrobial proteins to enter tissues
Pus accumulates at the site of inflammation
Pus:
A fluid rich in white blood cells, dead microbes, and cell debris

19. Pathogen Splinter Chemical signals Macrophage Mast cell Capillary
Fig
Pathogen
Splinter
Chemical
signals
Macrophage
Mast cell
Capillary
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

20. Pathogen Splinter Chemical signals Macrophage Fluid Mast cell
Fig
Pathogen
Splinter
Chemical
signals
Macrophage
Fluid
Mast cell
Capillary
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

21. Pathogen Splinter Chemical signals Macrophage Fluid Mast cell
Fig
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

22. Inflammation can be either local or systemic
Fever:
A systemic inflammatory response
Triggered by pyrogens released by:
Macrophages
Pathogen toxins
Septic shock:
A life-threatening condition
Caused by an overwhelming inflammatory response

23. Natural Killer Cells
All cells in the body (except red blood cells) have:
A class 1 MHC (major histocompatibility) protein on their surface
Cancerous or infected cells no longer express this protein;
Natural killer (NK) cells attack these damaged cells

24. Innate Immune System Evasion by Pathogens
Some pathogens avoid destruction by:
Modifying their surface to prevent recognition
Or by:
Resisting breakdown following phagocytosis
One such disease:
Tuberculosis (TB)
It kills more than a million people a year

25. In acquired immunity, lymphocyte receptors provide pathogen-specific recognition
Lymphocytes:
White blood cells
Recognize and respond to antigens (foreign molecules)
Two types:
T cells:
Mature in the thymus above the heart
B cells:
Mature in bone marrow

26. Lymphocytes contribute to:
contribute to immunological memory (an enhanced response to a previously encountered foreign molecule)
Cytokines:
Substances secreted by macrophages and dendritic cells to:
Recruit and activate lymphocytes

27. B
Break Slide
Tue, July 50, 2013

28. Acquired Immunity: An Overview
B cells and T cells:
Have receptor proteins
Such receptors can bind to foreign molecules
Each individual lymphocyte is specialized to:
Recognize a specific type of molecule

29. Antigen Recognition by Lymphocytes
An antigen:
Is any foreign molecule to which a lymphocyte responds
A single B cell or T cell has:
About 100,000 identical antigen receptors

30. Figure 43.9 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
(a) B cell receptor
(b) T cell receptor

31. Antigen- binding site Antigen- binding site V Disulfide bridge V V V
Fig. 43-9a
Antigen-
binding
site
Antigen-
binding site V
Disulfide
bridge V V V
Variable
regions C C
Constant
regions C C
Light
chain
Transmembrane
region
Figure 43.9 Antigen receptors on lymphocytes
Plasma
membrane
Heavy chains
B cell
Cytoplasm of B cell
(a) B cell receptor

32. Antigen- binding site Variable regions V V Constant regions C C
Fig. 43-9b
Antigen-
binding
site
Variable
regions V V
Constant
regions C C
Transmembrane
region
Figure 43.9 Antigen receptors on lymphocytes
Plasma
membrane
 chain
 chain
Disulfide bridge
Cytoplasm of T cell
T cell
(b) T cell receptor

33. Epitope:
An antigenic determinant
All antigen receptors on a single lymphocyte recognize it (same epitope)
Plasma cells:
Produced by B cells:
ecrete proteins called antibodies or immunoglobulins

34. Antigen-binding sites
Fig
Antigen-
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

35. Active and Passive Immunization
Active immunity:
Develops naturally in response to infection
Also develops following immunization or vaccination
In immunization:
A nonpathogenic form of a microbe or part of a microbe is used to
Elicits an immune response to an immunological memory

36. Passive immunity:
Provides immediate, short-term protection
It is conferred naturally when:
IgG crosses the placenta from mother to fetus, or when
IgA passes from mother to infant in breast milk
It can be conferred artificially by:
Injecting antibodies into a nonimmuned person

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

38. Immune Rejection
Cells transferred from one person to another:
Can be attacked by immune defenses
This complicates:
Blood transfusions, or
The transplant of tissues or organs

39. Antigens on red blood cells determine whether a person has blood type:
Blood Groups
Antigens on red blood cells determine whether a person has blood type:
A (A antigen)
B (B antigen)
AB (both A and B antigens), or
O (neither antigen)
Antibodies to nonself blood types:
Exist in the body
Transfusion with incompatible blood: :
Leads to destruction of the transfused cells
Recipient-donor combinations:
Can be fatal or safe

40. Tissue and Organ Transplants
MHC molecules:
Are different among genetically nonidentical individuals
Differences in MHC molecules stimulate:
Rejection of tissue grafts and organ transplants

41. Chances of successful transplantation increase:
If donor and recipient MHC tissue types are well matched
Immunosuppressive drugs facilitate transplantation
Lymphocytes in bone marrow transplants:
May cause the donor tissue to reject the recipient

42. Disruption in immune system function can elicit or exacerbate disease
Some pathogens have evolved to diminish the effectiveness of host immune responses
If the delicate balance of the immune system is disrupted, effects range from minor to often fatal

43. Allergies
Allergies are:
Exaggerated (hypersensitive) responses to antigens called allergens
In localized allergies such as hay fever:
Follow 1st exposure to an allergen
Allergen attaches to receptors on mast cells
Mast cells produced histamine
Triggers the production of IgE antibodies

44. IgE Histamine Allergen Granule Mast cell Fig. 43-23
Figure Mast cells, IgE, and the allergic response
Mast cell

45. The next time the allergen enters the body:
It binds to mast cell–associated IgE molecules
Mast cells release:
Histamine & other mediators
That cause vascular changes leading to typical allergy symptoms
An acute allergic response can lead to:
Anaphylactic shock (a life-threatening reaction) that can occur within seconds of allergen exposure