1. Immune System Chapter 18

2. 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!

3. 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!

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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

10. 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!!

11. 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

12. 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

13. 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.”

14. Cytotoxic T Cells & MHC

15. Acquired Immunity B) Helper T Cells
When activated by binding to MHC protein of an antigen presenting cell, Helper T-cells 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!

16. 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

17. 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”

18. 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

19. 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.

20. Passive vs. 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

21. 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.