1. Defense Systems for Your Body
IMMUNITY
Animals and plants are constantly under attack by pathogens.
Defense Systems for Your Body

2. Virus vs. Bacteria Colds and influenza are caused by viruses.
Viruses are which is a non-living particle that contains genetic material, and hijacks your cells to reproduce.
Viruses cannot be “killed” with antibiotics.

3. Virus vs. Bacteria
Bacteria are living organisms that have a metabolism, have DNA, and can reproduce on their own.
Bacteria can be killed with antibiotics because these substances target key processes in bacteria, such as production of the bacterial cell wall.

4. Body Defenses

5. Immune System Overview
The immune responses of animals can be divided into innate immunity and acquired immunity.

6. INNATE IMMUNITY BARRIER DEFENSE INTERNAL DEFENSE Skin Mucous Membranes
In innate immunity, recognition and response rely on shared traits of pathogens.
BARRIER DEFENSE
INTERNAL DEFENSE
Skin
Mucous Membranes
Secretions
Phagocytic cells
Antimicrobial proteins
Inflammatory Response
Natural killer cells

7. Barrier Defenses Skin tissues block the entry of many pathogens.
Mucus (from mucous membranes) traps pathogens.
Tears/Saliva wash away epithelial surfaces
Also contain enzymes (lysozyme) that can break down cell walls.
Sweat gland lower the pH of the human skin to 3 to 5 which destroys pathogens as well.

8. Internal Defenses Phagocytosis Macrophages Neutrophils
Some of these phagocytic cells move around the body, while others reside permanently in various organs and tissues.

9. Inflammatory Responses
Pain and swelling due to signaling molecules released during injury or infection.
Inflammatory Signaling Molecule = Histamine
Inflammation is signaled by mast cells, which release histamine.
Histamine causes fluids to collect around an injury to dilute toxins. This causes swelling.
The temperature of the tissues may rise, which can kill temperature-sensitive microbes.

10. Inflammatory Responses

11. Inflammatory Responses
Increased phagocytosis leads to the formation of pus, a fluid rich in white blood cells, dead microbes, and cell debris.

12. The Black Plague
Doctors would often wear masks laced with potpourri, flowers, spices, etc. to avoid the rotting smell of death.
Characteristics of bacterial infection: smell, change in pH in surrounding tissue, rotting flesh, change in texture of tissue

13. ACQUIRED IMMUNITY Specific Defense Major Players
Specific defenses are those that give us immunity to certain diseases.
In specific defenses, the immune system forms a chemical “memory” of the invading microbe. If the microbe is encountered again, the body reacts so quickly that few or no symptoms are felt.
The major players in the immune system include:
Macrophage
T cells (helper, cytotoxic, memory)
B cells (plasma, memory)
Antibodies
B and T cells are in a larger class of molecules called lymphocytes.

15. Some Vocabulary
Antibody: a protein produced by the human immune system to tag and destroy invasive microbes.
Antibiotic: various chemicals produced by certain soil microbes that are toxic to many bacteria. Some we use as medicines.
Antigen: any protein that our immune system uses to recognize “self” vs. “not self.”

16. Antibodies Antibodies are assembled out of protein chains.
There are many different chains that the immune system assembles in different ways to make different antibodies.

17. Antibodies as receptors
Antibodies can attach to B cells, and serve to recognize foreign antigens.

18. Antigens as effectors
Free antibodies can bind to antigens, which “tags” the antigen for the immune system to attack and destroy.

19. Antigen recognition
Cells of the immune system are “trained” to recognize “self” proteins vs. “not self” proteins.
If an antigen (“not self”) protein is encountered by a macrophage, it will bring the protein to a helper T-cell for identification.
If the helper T-cell recognizes the protein as “not self,” it will launch an immune response.

20. Helper T Cells
Helper T-cells have receptors for recognizing antigens. If they are presented with an antigen, they release cytokines to stimulate B-cell division.
The helper T-cell is the key cell to signal an immune response. If helper T-cells are disabled, as they are in people with AIDS, the immune system will not respond.

21. B Cells
B-cells in general produce antibodies. Those with antibodies that bind with the invader’s antigen are stimulated to reproduce rapidly.
B-cells differentiate into either plasma cells or memory B-cells. Plasma cells rapidly produce antibodies. Memory cells retain the “memory” of the invader and remain ready to divide rapidly if an invasion occurs again.

23. Helping the Immune System
Medical science has created to systems for augmenting the human immune system:
Antibiotics (NOT the same as antibodies)
Vaccines

24. How antibiotics work
Antibiotics help destroy bacteria (but not viruses).
Antibiotics work in one of several ways:
Slowing bacteria reproduction.
Interfering with bacterial cell wall formation.

25. How vaccines work
Modern vaccines are created from killed bacteria or viruses, or fragments of proteins from these microbes.
The proteins are recognized as antigens by our immune systems. This causes a mild immune response. Memory T-cells and B- cells remain ready to fight off the illness if it is encountered again.