This document provides an overview of the human immune system and its defenses against disease. It discusses the external barriers of skin and mucus, internal responses like phagocytosis and inflammation, and the adaptive immune system involving B and T cells and antibody production. It covers active and passive immunity, immune responses, antigen recognition, and immune system disorders like autoimmunity, allergy, and AIDS. The immune system provides multilayered defenses that have largely evolved to protect the body from infectious diseases, toxins, and other foreign invaders.

1. CHAPTER 43
THE BODY’S
DEFENSES

2. The Nature of Disease
• Pathogenic Organisms
• Genetic Disorders
• Toxic Chemicals
• Other Environmental Factors
• Physical Damage to Organs
• Nutritional Disorders

3. Types of Pathogenic
Organisms
• Viruses
• Bacteria
• Protozoan
• Fungi
• Animal
• Parasites

4. Mechanisms of
Disease by Pathogens
• Utilization of host nutritional
resources
• Physical damage to host tissues
• Production of toxic substances
• Chromosomal and gene damage
• Body cells behave abnormally

5. Viruses
capsid
envelope
nucleic acid

6. Bacteria
cell wall
plasma
membrane
cytoplasm
circular DNA

7. Defense Mechanisms
1. External defense
2. Internal Defense
3. Immune Defense

8. 1st Line of Defense
• Skin acts as barrier to microbes and viruses
- sweat has a low pH
• Mucus traps foreign particles
• Tears
- Lysozyme has antimicrobial action
• Gastric stomach acid

9. Body Coverings: The Skin
sebaceous
glands
sweat gland
epidermis

10. Body Coverings:
Mucous Membranes
mucus
cilia
columnar
epithelium

11. 2nd Line of Defense
• Phagocytic cells (WBCs)
- N L M E B
- Natural Killer (NK) Cells: attack virus
infected cells
• Inflammatory Response
• Antimicrobial proteins
- Lysozyme
- Interferon
- Antibodies

12. Nonspecific Phagocytosis
Neutrophils
Monocytes
Eosinophils

13. Mechanism of Phagocytosis
Mechanism of Phagocytosis
Macrophage

14. Lymphatic System

15. Inflammatory Response
Histamine &
prostaglandins
released
Capillaries dilate
Clotting begins
Chemotactic
factors attract
phagocytic cells
Phagocytes
consume
pathogens &
cell debris

16. Characteristics of Immunity
• Recognition of self versus non-self
• Response is specific
• Retains a “memory” allowing an
accelerated second response
• Can respond to many different
materials
• Involves lymphocytes and
antibodies

17. Types of Immunity
• Active Immunity
- Naturally-Acquired Active Immunity
- Artificially-Acquired Active Immunity
• Passive Immunity
- Naturally-Acquired Passive Immunity
- Artificially-Acquired Passive Immunity

18. Types of
Acquired
Immunity

19. Active Immunity
• The production of antibodies against a
specific disease by the immune system.
• Naturally acquired through disease
• Artificially acquired through vaccination
– Vaccines include inactivated toxins, killed
microbes, parts of microbes, and viable but
weakened microbes.
• Active immunity is usually permanent

20. • A vaccinated person has a secondary
response based on memory cells when
encountering the specific pathogen.
– Routine immunization against infectious
diseases such as measles and whooping
cough, and has led to the eradication of
smallpox, a viral disease.
– Unfortunately, not all infectious agents are
easily managed by vaccination.
• HIV vaccine in the works

21. Passive Immunity
• Passive Immunity- Protection
against disease through antibodies
produced by another human being
or animal.
• Effective, but temporary
• Ex. Maternal antibodies
• Colostrum.

22. • Passive immunity can be transferred
artificially by injecting antibodies from an
animal that is already immune to a disease
into another animal.
– Rabies treatment: injection with antibodies
against rabies virus that are both passive
immunizations (the immediate fight) and active
immunizations (longer term defense).

23. Immune System Response to
Antigens
Humoral Immunity
• Involves antibodies (secreted from B
cells) dissolved in the blood plasma.
• Demonstrated as a immune response
using only the blood serum.
• Defense against bacteria, bacterial
toxins, & viruses.

24. Immune System Response to
Antigens
Cell-Mediated Immunity
• Involves the activities of specific
white blood cells (T cells).
• Defense against cancer cells, virus-infected
cells, fungi, animal parasites,
& foreign cells from transplants.

25. Lymphocyte Formation

26. B Cells
• Mature in bone marrow
• Involved in humoral immunity
• Once activated by antigen,
proliferate into two clones of cells:
plasma cells that secrete
antibodies and memory cells that
may be converted into plasma cells
at a later time

27. B Cells
antibodies

28. B Cells
B Cells

29. Activation of B Cells by
Antigen
antigen

30. Clonal Selection

31. Clonal Selection
plasma cells memory cells
antibodies

32. Humoral Immune Response
time (days)
antibody concentration
first
exposure to
antigen A

33. Humoral Immune Response
time (days)
antibody concentration
first exposure
to antigen A
primary response:
concentration of
anti-A antibody second exposure
to antigen A

34. Humoral Immune Response
time (days)
antibody concentration
secondary response:
concentration of anti-A
antibody
second exposure
to antigen A
first exposure
to antigen B

35. Humoral Immune Response
time (days)
antibody concentration
primary
response:
concentration of
anti-B antibody
first
exposure to
antigen B

36. • Antibodies constitute a group of globular
serum proteins called immunoglobins
(Igs).
– A typical antibody molecule has two identical
antigen-binding sites specific for the epitope
that provokes its production.

37. Antibody Molecule
antigen binding sites
antigen
light chains heavy chains

38. Mechanisms on Antibody
Action
• Precipitation of soluble antigens
• Agglutination of foreign cells
• Neutralization
• Enhanced phagocytosis
• Complement activation leading to cell lysis
• Stimulates inflammation

39. • The binding of antibodies to antigens to form
antigen-antibody complexes is the basis of
several antigen disposal mechanisms.

40. The classical complimentary pathway,
resulting in lysis of a target cell

41. Immunoglobin Classes
IgM
• 1st response to antigen
• Effective in agglutination
• Can’t cross placenta
IgG
• Most common form
• Crosses blood vessels
• Crosses placenta
(passive immunity to
fetus)
IgA
• Secreted from mucus
membranes
• Prevents attachment of
bacteria to epithelial surface
• In colostrum
IgD
• B cell activation
• Can’t cross placenta
IgE
• Histamine
reactions and
allergies

42. Overview of Immune System Responses

43. T Cells
• Mature in thymus
• Involved in cell-mediated immunity
• Activated when another cell
presents antigen to them
• Several types of T cells: cytoxic T
cells, helper T cells, suppressor T
cells, and memory T cells

44. T Cells
• There are two main types of T cells, and
each responds to one class of MHC
molecule.
– Cytotoxic T cells (TC) have antigen receptors
that bind to protein fragments displayed by the
body’s class I MHC molecules.
– Helper T cells (TH) have receptors that bind to
peptides displayed by the body’s class II MHC
molecules.

45. Cytotoxic T Cell
perforin
pores in target cell

46. Helper T Cells
T cell receptor
helper
T cell
bacterium
bacterial
antigens
macrophage interleukin 1

47. The central role of helper T cells

48. • The central role in Helper T cells in an
infected cell

50. –T-independent antigens
• T cells activated by binding to certain
antigens
• No memory cells generated
•Weaker response than t-dependent
–T-dependent antigens
• Most antigens require co-stimulation to
evoke a B-cell response
• Antibody production stimulated with help
from TH
• Most antigens are t-dependent

51. • T-dependent
antigens- can trigger a
humoral immune
response by B cells
only with the
participation of helper T
cells.

52. Tissue/Organ Transplants
• Major Histocomatibility Complex
(MHC)
- Bone marrow
- Organs

53. Abnormal immune function can
lead to disease
• Malfunctions of the immune system can
produce effects ranging from the minor
inconvenience of some allergies to the
serious and often fatal consequences of
certain autoimmune and immunodeficiency
diseases.

54. Abnormal Immune
Function
• Autoimmune Disease
• Allergy
• Immunodeficiency

55. Autoimmune Disease
• Rheumatoid arthritis
• Type I Diabetes
• MS
• Lupis
• Crohn’s disease
• Grave’s disease

56. ABO Blood Types
Phenotype Genotype
O i i
A I A I A or I A i
B I B I B or I B i
AB I A I B

57. ABO Blood Types
Type
A
Produces
anti-B
antibodies
b
b
b
b
b
b
b
b

58. ABO Blood Types
Type
B
Produces
anti-A
antibodies
a
a
a
a
a
a a
a
a
a

59. ABO Blood Types
Type
AB
Produces
neither
anti-A nor
anti-B
antibodies

60. ABO Blood Types
Type
O
Produces
both anti-A
and anti-B
antibodies
a
a
a
a
a
a
a
a
a
a
b
b
b
b
b
b
b
b

61. Rh Factor
and
Pregnancy
RH+ indicates protein
RH- indicates no protein
15% of population is RH-

62. Rh Factor
and
Pregnancy
Rh+ mother w/Rh- baby– no problem
Rh- mother w/Rh+ baby– problem
Rh- mother w/Rh- father– no problem
Rh- mother w/Rh- baby-- no problem
RhoGAM used @ 28 weeks

63. Allergy (Immune Hypersensitivity)
• Hypersensitive response to certain
environmental allergens
• Food, pollen, pet dander, asthma, bee
sting
• Anaphylactic shock
- epinephrine

64. • Mast cells, IgE,
and the allergic
response.

65. AIDS
Problems
Acquired Immunodeficiency
Syndrome
HIV (virus) attacks T-cells
Weakens or eliminates immune
system
Susceptible to many fatal diseases

66. • Transmission of HIV requires the transfer of
body fluids containing infected cells, such as
semen or blood, from person to person.
– Unprotected sex
– Nonsterile needles
– HIV transmission among heterosexuals is
rapidly increasing as a result of unprotected sex
with infected partners.
– HIV in Africa and Asia- primarily by heterosexual
sex

67. AIDS
• In 1983, a retrovirus, now called human
immunodeficiency virus (HIV), had been
identified as the causative agent of AIDS.

68. • With the AIDS mortality close to 100%, HIV
is the most lethal pathogen ever
encountered.
– Molecular studies reveal that the virus probably
evolved from another HIV-like virus in
chimpanzees in central Africa and appeared in
humans sometimes between 1915 and 1940.
• These first rare cases of infection and AIDS went
unrecognized.

69. AIDS

70. AIDS

71. • HIV Testing:
– The HIV antibody test has be used to screen
all blood supplies in the U.S. since 1985.
• May take weeks or months before anti-HIV
antibodies become detectable.
- Drug treatment available
- Best prevention is education and protected sex