1. The Immune Stystem

2. The Immune System
The body must defend itself against potentially dangerous viruses, bacteria and other pathogens. It must also contend with abnormal cells and cell that may develop into cancer.
HIV
Cancer cells in
bone marrow

3. The Immune System
There are two types of defense that the body has to fight these threats.
Innate Immunity – a defense that is present from birth. Usually nonspecific responding to a broad range of microbes. Consists of external and internal barriers, phagocytic white blood cells called macrophages.
Acquired Immunity – also called adaptive immunity. Developes only after exposure to microbes, abnormal body cells, and toxins. Highly specific. White blood cells called lymphocytes are involved as well as proteins called antibodies.

4. Overview of defenses against bacteria viruses and other pathogens
INNATE IMMUNITY
Rapid Responses to a
broad range of microbes
ACQUIRED IMMUNITY
Slower responses to
specific microbes
External defenses
Internal defenses
Skin
Mucous membranes
Secretions
1st line of defense
Phagocytic Cells
Antimicrobial proteins
Inflammatory Response
Natural Killer Cells
2nd line of defense
Humoral Response
(antibodies)
Cell Mediated response (Cytotoxic lymphocytes)
3rd line of defense
Flu Virus

5. External Defenses:
These are the first line of defense from diseases

6. Skin is impenetrable to viruses or bacteria.
Tiny cuts may allow penetration of pathogens.

7. Mucous membranes
line the respiratory, digestive and genitouterary tracts block entry of pathogens. Cells of these membranes produce mucus which traps microbes.
Ex: The trachea has ciliated epithelial cells that
sweep mucus and any trapped debris upward away from the lungs.

8. Secretions Saliva, tears - wash away surfaces of epithelial cells.
Sebaceous (Oil) glands and sweat glands - give the skin a pH ranging from 3 -5 which is acidic enough to prevent the colonization of some microbes
Lysozyme – an enzyme contained in secretions from the skin that digests the cell walls of many bacteria (peptidoglycan)
Gastric Juices – acidic pH kills pathogens before they reach the intestines.
Exception: Hepatitis A virus can survive gastric acidity

9. Internal Defenses – 2nd Line
microbes that get past the external defenses must then contend with the internal mechanisms of innate defense.

10. Phagocytic Cells
phagocytosis is the ingestion of invading microorganisms by a certain type of wbc called phagocytes.
Phagocyte and
gonococci

11. Attach to their prey by way of surface receptors that bind to structures found on many microbes but not on regular body cells. An example of this structure is polysaccharides found on the surface of bacteria.
Engulfs the microbe(s) then forms a vacuole.
Vacuole fuses with a lysosome
Nitric oxide and other toxins poison the microbes
Enzymes breakdown the molecules that make up the microbe

12. 4 Types of White Blood Cells (leukocytes) that are phagocytic:
Neutrophils
Enter infected tissue and engulf microbes about 70% of wbc’s. Self destruct in a few days
Macrophages
“the big eater” large phagocytes that
engulf microbes and
dead tissue cells. Live longer than neutrophils

13. Eosinophils Dendritic Cells Attack large parasites
with enzymes (blood fluke)
Dendritic Cells
Ingest microbes like macrophages and stimulates acquired immunity

14. Antimicrobial proteins – proteins that become activated and secreted when there is an infection.
Examples include lactoferrin binds iron which is necessary for bacteria to grow and defensins which kill fungi
bacteria and viruses

15. Complement System - a group of proteins that lead to the lyses (bursting) of invading microbes.
Substances on the surface of microbes activate the complement system.

16. Interferons
Limit the spread of viruses by keeping them from replicating.

17. Inflammatory Response
Damage to tissue by physical injury or entry of pthogens leads to the release of chemical signals that trigger a response.
Histamine - a chemical stored in mast cells found in connective tissues. Histamine dilates capillaries and increases their permeability

18. Chemokines are small proteins that guide phagocytes to the site of injury
Macrophages release chemicals like prostoglandins that promote blood flow to the site of injury
Result is inflammation, redness, swelling.

19. Natural Killer Cells
NK cells patrol the body and attack viral infected cells and cancer cells
Once attached to an infected cell, it releases chemicals that cause the cell to undergo apoptosis (programmed cell death)
NK cells are not 100%
effective.