Chapter 43:
The Body’s Defenses
How does your body protect
you from invaders?
Immune System Review
Microorganism/Microbe
Pathogen
Antibiotic
Antibody
Antigen
Key Concepts
3 Lines of Defense
Innate vs. Acquired immunity
Phagocytes, Lymphocytes, Antibodies, etc…
Humoral vs. Cell-Mediated immunity
Distinguishing self from non-self
Tissue transplantation
Immune Diseases/Disorders
Using HIV to treat Cancer??
http://abcnews.go.com/WNT/video/doctors-hivtreat-cancer-17929437
What do you think?
How does your body INITIALLY defend itself
from invasion? (1st line – specific or non?)
What happens if the invader gets past the 1st
line? (2nd line – specific or nonspecific?)
What about more serious infections? (3rd line)
1st line Defense!!
Skin, mucus, cilia, saliva, acids, tears,
oils, bacteria, coughing, sneezing,
vomiting
Antimicrobial proteins & Lysozymes
Innate vs. Acquired Immunity
Innate Immunity:
– Present before exposure; since birth
– Includes natural bodily defenses, mother’s
milk, or casual exposure
– Broad-range capabilities, non-specific
– External defenses:
• skin, mucus membranes, tears
– Internal Phagocytic cells
• A.K.A.: “macrophages”; engulf invaders
Innate vs. Acquired Immunity
Acquired Immunity:
– Develops only after exposure
– Highly microbe-specific… how?
– Employ lymphocytes & antibodies
• Involves both Humoral & Cell-Mediated
responses
Innate Immunity:
Your first line of defense
Phagocytic White Blood Cells
Recognize & bind to carbohydrate
markers on foreign cell membranes
– Triggers receptor-mediated endocytosis
– Engulf & digest pathogens via
Phagocytosis
Types of
White Blood Cells
Neutrophils: 60-70% of
WBCs; engulf and
destroy microbes at
infected tissue; short lived
Monocytes: 5% of
WBCs; develop into….
Macrophages: “big
eaters” enzymatically
destroy microbes; can be
found in spleen, lymph
nodes, and other organs
Eosinophils: 1.5% of
WBCs; destroy large
parasites extracellularly
Natural killer (NK) cells:
trigger apoptosis in virusinfected cells & cancer
cells
Leukocyte vs. Lymphocyte
Leukocyte =
– White blood cells (WBC’s)
Lymphocyte =
– Specific type of WBC that mature and
migrate through the lymphatic system and
target specific antigens via antibodies,
receptors and toxin release
The Inflammatory Response
“Inflammation” = pain, swelling, fever,
redness, itching, and pus
Causes of Inflammation
Injuries
Exposure to microbes/pathogens
Exposure to foreign objects or
chemicals (insect bites, stings,
medications, etc)
Exposure to allergens (pollen, pet
dander, foods, etc)
Rare: sunlight, temperature, self!
The Inflammatory Response
3 Steps:
1. Tissue damage = release of chemical signals~
– Mast cells release chemicals known as Histamine &
Prostaglandins that trigger inflammation
2. Dilation increases permeability of capillaries~
– Increased blood flow; leukocytes leak out to infected area
– Delivery of clotting factors & antimicrobial proteins
3. Phagocytosis of pathogens~
– WBC’s engulf microbes or damaged tissue
– Fever: leukocyte-released chemicals increase body
temperature
Acquired Immunity:
Lymphocytes are the Key Defenders
Specific Immunity
Antigen:
– a foreign molecule that elicits a
response from a lymphocyte
Lymphocyctes:
– WBC’s that originate from stem cells in
bone marrow
– B Cells (mature in bone marrow)
– T Cells (mature in thymus)
Antibodies:
– antigen-binding immunoglobulin,
produced by B cells
Antigen receptors:
– membrane receptors on B and T cells
Ch. 43 Research:
Humoral vs. Cell-mediated Responses
B cells vs. T cells
Memory cells
Clonal selection
Autoimmune disease
T cells vs. B cells
B cells:
– Mature in Bone Marrow
– Target in-tact Antigens
– Part of Humoral Response
T cells:
– Mature in Thymus
– Target antigen fragments bound to
MHC molecules on Infected Cells
– Part of Cell Mediated Response
Humoral vs. Cell-Mediated
Humoral immunity
B cell activation
Production of antibodies
Defend against intact antigens free in
the lymph and blood plasma
– (bacteria, toxins, and viruses)
Humoral response: B cells
Stimulated by an antigen-presenting
macrophage (WBC w/ a germ on it)
Activates Helper T cells
T cells secrete cytokine chemicals that
activate B cells
B cells differentiate into memory B cells
and antibody-producing plasma cells
Cytokines
Cytokine:
– Proteins secreted by phagocytic cells
(macrophages, etc.) and T-helper cells
– Activate Lymphocytes (B & T cells)
Humoral Response:
1.
2.
3.
4.
B cells activate.
Plasma cells secrete antibodies.
Antibodies attach to antigens.
Antigens agglutinate (stick
together) & get disposed.
5. Macrophages phagocytose or lyse
the cell.
Cell-Mediated
Cell-mediated immunity
T cells are activated.
T cells bind to and/or lyse infected
cells.
Defend against cells infected with
bacteria, viruses, fungi, protozoa,
parasites, even cancer!
Cell-mediated Response
1) Cell surface molecules expose
antigens (foreign proteins).
2) Cytotoxic T cell releases perforin, a
protein that forms pores in the target
cell membrane.
– causes cell lysis and exposes pathogens to
circulating antibodies for disposal
Humoral Response
In Tact Antigens
B Cell Activation
Secrete antibodies
that defend
against pathogens
& toxins in
extracellular fluid
Cell Mediated Response
Antigens on
Infected Cells
T Cell Activation
Defend against
infected cells,
cancer and
transplanted
tissues
Clonal Selection
Clonal selection:
– antigen-driven cloning of lymphocytes
Effector cells:
– short-lived cells that combat the antigen initially
Memory cells:
– long-lived cells that bear receptors for the antigen
and activate upon subsequent exposure.
Active vs. Passive Immunity
Active: natural exposure to antigens
causes one’s own lymphocytes to
activate and produce antibodies
– May also be acquired by Immunizations
Passive: direct transfer of antibodies
through placenta or mother’s milk
HIV
Human Immunodeficiency Virus
Causes AIDS (Acquired Immune
Deficiency Virus)
HIV (a retrovirus) attacks helper T cells
by binding with their cell receptor (CD4)
This impacts both the Humoral and
Cell Mediated responses

Clonal Selection Hypothesis
Each lymphocyte bears one specific type of
receptor.
Receptor/antigen binding is required for cell
activation.
Activated lymphocytes divide and give rise to
cells with identical receptors to the parent.
– This is how your immune system “remembers” a
pathogen later!
Clonal Selection
Hypothesis
First, those lymphocytes
bearing receptors compatible
to “self” tissues are destroyed
(3)
Second, those bearing
receptors that match foreign
antigens are activated then
cloned (5/6)
Self/Nonself Recognition
Self-tolerance:
– Capacity to distinguish self from non-self
molecules
Autoimmune diseases:
– Failure of self-tolerance mechanisms
– Multiple sclerosis, lupus, rheumatoid arthritis,
insulin-dependent diabetes mellitus, Crohn’s
disease
Abnormal immune function
Allergies:
– hypersensitive responses to environmental antigens (allergens)
– causes dilation and blood vessel permeability
– Histamines are released from Mast cells
Autoimmune disease:
–
–
–
–
multiple sclerosis
Lupus
rheumatoid arthritis
insulin-dependent diabetes mellitus
Immunodeficiency disease:
– SCIDS (bubble-boy)
– A.I.D.S. (HIV)
Cancer & the Immune System
Tumor cells are targeted by both
Cytotoxic T cells and Natural Killer (NK)
cells
– How might some tumors escape
detection??
Treg research: Article Review
What are “Regulatory T Cells” (Tregs)?
What is their role in immunity?
How might they be linked with cancer?
– Article: “Regulatory T cells and tumour
immunity – observations in mice and men”
by Gallimore and Godkin, 2007
Major Histocompatibility Complex
Aka: “MHC”
Cell surface proteins that display
fragments of antigens or processed
proteins on the cell surface
Epitope:
– region of antigen surface
recognized by antibodies
Induction of Immune Responses
Primary immune response:
– lymphocyte proliferation and differentiation the 1st
time the body is exposed to an antigen
Plasma cells:
– antibody-producing B-cells
Secondary immune response:
– immune response if the individual is exposed to
the same antigen at a later time~ Immunological
memory
Types of Immunoglobins
IgM:
– 1st to circulate; indicates infection; too large to cross
placenta
IgG:
– most abundant; crosses walls of blood vessels and placenta;
protects against bacteria, viruses, & toxins; activates
complement
IgA:
– produced by cells in mucous membranes; prevent
attachment of viruses/bacteria to epithelial surfaces; also
found in saliva, tears, and perspiration
IgE:
– very large; small quantity; releases histamines-allergic
reaction
Antibody-Mediated Antigen Disposal
Neutralization (opsonization):
– antibody binds to and blocks antigen activity
Agglutination:
– antigen clumping
Precipitation:
– cross-linking of soluble antigens
Complement fixation:
– lyses viruses and pathogenic cells & activates cell
surface proteins to break down the cell
Immunity in Health & Disease
Active immunity:
– natural: conferred immunity by recovering from disease
– artificial: immunization and vaccination; produces a
primary response
Passive immunity:
– transfer of immunity from one individual to another
– natural: mother to fetus; breast milk
– artificial: rabies antibodies
ABO & Rh blood groups (antigen presence)