Download The Immune System

Immune System
Chapter 18
What is its function?
PROTECTION FROM INVADERS!
 Three Lines of Defense:


Innate Immunity- born with it!
• 1. Barrier Defenses – BROAD
• 2. Internal Cellular Defenses - BROAD
• 3. Acquired Immunity –develops only after
exposure to a SPECIFIC pathogen!
1. Barrier Defenses / 1st line of
defense

The Skin and Mucous Membranes
Physical barriers; trap microbes
 Secrete substances (oil, sweat, etc.)
that makes the skin too acidic
(pH= 3-5) for microbes to live there.
 Also secrete lysozyme, an enzyme
that can destroy bacterial cell walls (in
saliva, mucous secretions, & tears.)
 INNATE=you’re born with it!

2. Internal Cellular Defenses

If an invader gets inside the body, the internal
defenses (2nd line of defense!) take over
 A) Phagocytes (“to eat”/”cell”)
• White blood cells that “eat”/engulf invaders
• NEUTROPHILS-most numerous phagocyte
• MONOCYTES BECOME MACROPHAGES
(can patrol lymphatic system/ spleen, lymph nodes
for pathogens)
• EOSINOPHILS- phagocytize parasitic invaders
• Invaders (bacteria/virus/etc) are then digested by
lysosomes.
2. Internal Cellular Defenses
 B)

Antimicrobial Proteins
Interferon = “Warning Protein” sent out by
virus infected cells.
• Other body cells then make other substances
to inhibit viral replication.

Complement System- 30 proteins w/
variety of functions. Many lyse invaders.
2. Internal Celluar Defenses

C) Inflammatory Response

Damage to tissue (from physical injury or the
entry of pathogens) leads to inflammation
• Histamine (signal molecule) is released by
basophyls & mast cells (leukocytes).
• This causes increased vasodilation & & increased
permeability of capillaries. (Clotting factors, platelets,
phagocytes, etc. diffuse into interstitial fluid to help
REPAIR) Redness, edema, & increased temperature occur.
2. Internal Cellular Defenses

D) Natural Killer (NK) Cells- Patrol
the body and attack virus-infected
cells and cancer cells
• Surface receptors (“nametags”) identify these
infected/damaged cells

All 4 of these internal defenses
(phagocytes, interferons, inflammatory
response, and natural killer cells)
occur INNATELY.
3. Acquired Immunity
Acquired immunity is the third line of
defense.
 Acquired immunity only comes after
EXPOSURE to a specific pathogen.
 Receptor proteins in cell membrane
provide pathogen-specific recognition.
 Acquired immunity occurs more slowly
than innate immunity.

3. Acquired Immunity

Acquired immunity is
performed by
lymphocytes


Made from stem
cells in the bone
marrow
B-cells:
• mature in the bone
marrow

T-cells:
• mature in the thymus
3. Acquired Immunity


Antigen = foreign molecule
that is recognized by
lymphocytes and causes
them to respond
 An antigen is usually a
surface marker
(“nametag”)
Lymphocytes
 Have antigen receptors
(100,000 on each cell!)
that recognize a
SPECIFIC antigen by
shape
 SPECIFIC!!
3. Acquired Immunity

B-lymphocytes are
responsible for the humoral
immune response



They are responsible for
pathogens OUTSIDE of
cells (in body fluids, etc.)
B-lymphocyte is
“activated” when specific
antigen binds to its
receptors.
Activated B-lymphocytes
reproduce using clonal
selection in order to
destroy the invader
3. Acquired Immunity

These B-lymphocytes
produce two types of cloned
cells:

Effector cells (Plasma
Cells)
• Make antibodies!
• Special proteins that bind
onto the ANTIGENS of the
“invaders,” which flags them
for destruction (usually by
macrophages)

Memory cells
• These cells live a long time,
and can respond quickly if
this same antigen is seen
again
3. Acquired Immunity

T-lymphocytes are responsible for the
cell-mediated immune response


Guard against invaders hiding out inside infected cells
A) Cytotoxic T cells
• They are the effectors (“hit men”) of the cell-mediated immune
response by lysing infected cells or “punching holes” in the
membrane
• They kill infected body cells (display foreign antigens on Major
Histocompatability Complex (MHC) or other cells that don’t belong
(like tumors)
• Class I MHCs = on almost all body cells except RBCs.
• Class II MHCs= made by dendritic cells, macrophages, & B cells.
• Some of these cells will become memory cells, so they can be
reactivated if the pathogen “strikes again.”
Cytotoxic T Cells & MHC
Acquired Immunity
B) Helper T Cells
• When activated by binding to MHC protein
of an antigen presenting cell, Helper Tcells secrete cytokines (like interleukin)
which stimulate & activate B cells &
Cytotoxic-T cells.
• “Master Switch of acquired immunity”
• HIV destroys Helper T cells, and shuts down
both humoral & cell-mediated immunity!
Primary v. Secondary
Immune Response
 Primary
Response
• Upon first exposure to an antigen, the
immune response is delayed for several
days while plasma cells are being formed
 Secondary
Response
• If antigen is seen again, the next response
is quicker and more potent because of
memory cells
The Immune System

Key Features of the Immune System

Specificity
• Recognizes SPECIFIC invaders – species of
bacteria, for example
• Due to ANTIGENS dispayed on the MHC
(Major Histocompatibility Complex)
• Diversity
• The immune system can respond to millions of
different invaders because it has so many
different lymphocytes “on reserve”
The Immune System

Key Features of the Immune System

Memory
• The immune system can “remember” antigens it’s seen
before and react more quickly the second, third, etc. time
it sees them
• Acquired immunity
• Because of memory cells (B & T cells)!

Self/Nonself Recognition
• The immune system can distinguish between the body’s
own molecules from foreign molecules
• Autoimmune disorders (example: lupus, MS,
rheumatoid arthritis) means that this part of the immune
system is not working – the immune system destroys the
body’s own tissues
Passive vs. Active Immunity

Passive Immunity



Transferring antibodies from one person to
another, without the B-lymphocytes having
to make them!
The person will already have the memory
cells and antibodies, so the next response
will be quicker!
Example:
• Pregnant mother passes antibodies to her fetus
through the placenta
• Antibodies in breast milk
• Immunoglobulins (antibodies) may be given to a
person who is exposed to a disease to prevent
them from getting the disease.
Passive vs. Active Immunity

Active Immunity


Immunity to a specific pathogen
that comes after having come in
contact with the pathogen.
Can come naturally
• Been sick with the pathogen
before
• Example: had measles before,
2nd time won’t take as long to
respond

Can come artificially
• Immunization (weakened or dead
form of the pathogen is used to
induce immune response.)
• Edward Jenner - smallpox
• Stimulates B-lymphocytes to
make antibodies AND memory
cells
Allergies
Allergies are hypersensitivies of the
immune system to an environmental
molecule because of its ANTIGENS
 Anaphylactic shock

Life-threatening allergic reactions to
ingested or injected allergens
 Peanuts, shellfish, bee stings, etc.
