1. Dynamic Defense System
Ch 43 Notes

2. Pathogens Infectious Agents that cause disease
Viruses, bacteria, protists and fungi may be pathogens
Animals fight back using immune cells

3. Innate Immunity Found in all animals Active immediately upon infection
Includes: barriers (skin), internal defenses
Made of preset group of receptors that binds to a molecule absent from animal bodies but found in microbes

4. Acquired Immunity Found only in vertebrates
Activated after innate immune defense
Enhanced by previous exposure to pathogen
Very specific

6. Innate Immunity of Invertebrates
Exoskeleton – first line of defense
Chitin effective against most pathogens
Lysozyme – enzyme that digests microbial cell walls – blocks pathogens in digestive system
Phagocytosis – Ingestion and digestion of bacteria/foreign substances – fights pathogens that get through exoskeleton
Antimicrobial peptides – circulate through insect bodies to kill fungi and bacteria

7. I. Innate Immunity of Vertebrates
A. Barrier Defenses
1. Intact skin – barrier that can’t normally be penetrated by microbes
2. Mucous membranes – line digestive, respiratory and urogenital tract
a. Mucus – fluid secreted by mucous membranes – traps microbes and is removed from body by cilia (tiny hairs)
b. Acid – produced in stomach destroys microbes before they go into the digestive tract
Lysozyme – destroys bacteria in respiratory tract and eyes
Sweat and oil glands have low pH to kill bacteria

8. Cellular Innate Defenses
1. Phagocytic white blood cells
Use TLR receptors to recognize pathogens
TLR triggers internal defenses
Phagocyte traps microbe, engulfs it, makes a vacuole, fuses with lysozyme, kills microbe
Neutrophils
Most numerous WBC
Infected tissue sends signals which call out neutrophils
Neutrophils engulf and destroy

10. Cellular Innate Defenses
Monocytes
enter into damaged tissue and form macrophages
attach to microbe’s surface, “eat” it and destroy it using lysosomes – YUM!!
macrophages live permanently in lungs, liver, kidney, brain, lymph nodes and spleen
If microbe is in blood – trapped in spleen
If microbe is in interstitial fluid – trapped in lymph

12. Cellular Innate Defenses
c. Eosinophils
*defend against large parasites (eeww)

13. Antimicrobial Peptides and Proteins
Interferons – proteins that provide defense against viral infections
Cells infected with virus sends out interferons
Cause uninfected cells nearby to produces substances to fight off virus
Limits cell to cell spread

14. Antimicrobial Peptides and Proteins
Complement System- 30 proteins in blood plasma
Fight infections
Circulate in an inactive state
Get activated by microbes
Causes cascade of reactions leading to lysis of invading cells

15. Inflammatory Responses
Response to tissue damage (from injury) or to entry of microorganisms
Histamine – released by mast cells at site of tissue damage
Arterioles dilate (open) and venules constrict (shrink) so that the blood supply increases in the area (swelling and redness)
*aid in blood clotting and repair
*block spread of microbes

16. Inflammatory responses
During inflammation – signals sent out
Antimicrobial proteins go to site
More histamine is released
Phagocytes attracted
Neutrophils and macrophages are called in
Ends with accumulation of Pus – filled with WBC’s, dead microbes and cell debris – YUM!!

18. Natural Killer Cells
Help recognize and eliminate certain diseased cells in vertebrates
Cells have class I MHC molecules on their surface
When a virus infects or cell becomes cancerous, cells stop expressing the MHC protein
Natural Killer cells attach to these damaged cells and cause them to die preventing spread

19. Evasion by Pathogens Some pathogens can avoid being destroyed
Some bacteria have capsules that hide polysaccharides in the cell walls and don’t get recognized (like strep pneumoniae)
Some bacteria are resistant to breakdown after phagocytosis (like TB)

20. Acquired Immunity Pathogen specific response
Specific response to an invader (not general defense like innate defenses

21. Acquired Immunity Lymphocytes – WBC’s
2 Types – B lymphocytes (B cells) and T lymphocytes (T cells)
circulate through blood and lymph and are concentrated in lymph nodes and spleen
Contribute to Immunological Memory– recognize and respond to a specific foreign invader that has been encountered previously

22. Acquired Immunity
Antigen – foreign molecule that causes a response by lymphocyte
can be found on viruses, bacteria, fungi, protozoa, parasitic worms
also found on pollen (allergies) and transplanted tissue (like heart transplant)
B cells and T cells recognize antigens using Antigen Receptors

23. Acquired Immunity B Cells (form and mature in Bone marrow)
Produce antibodies that are specific to a particular antigen
*5 classes of antibodies (IgA, IgD, IgE, IgG, IgM)
*Structure of antibodies is basically the same except for a variable region that makes the antibody recognize specific antigens
*Antibody binds to intact antigen and inactivates it
*Macrophage comes and eats it

25. II. Specific Line of Defense – IMMUNE SYSTEM
T Cells (form in bone marrow and mature in Thymus gland)
Only bind to antigen fragments that are on the surface of host cells
recognize nonself cells
if nonself cell is identified, T cells divide rapidly and produce
Cytotoxic T cells (killer T cells) that puncture non-self cells and make them burst
Helper T cells – stimulate more B cells and killer T cells to form to help fight the invader faster

26. Acquired Immunity T Cell receptors Have alpha and beta chain
Also have constant region and variable region

27. Acquired Immunity MHC – Major Histocompatability Complex
Helps immune system tell the difference between self (you) and nonself (invader)
MHC is unique to all individuals (except identical twins or clones )
Class I
found on almost all cells of body
Bind peptide fragments of foreign antigens
If body cell is infected or cancerous, it makes foreign antigens and displays them
Cytotoxic T cells recognize these antigens and kill the infected cells

28. Acquired Immunity MHC II
Made by dendritic cells, macrophages and B cells
Bind to foreign materials that have been taken in by phagocytosis
Cytotoxic and Helper T cells recognize them

29. Amplifying Lymphocytes
Binding of an antigen receptor to its specific antigen initiates events that activate the lymphocyte
B Cells and T cells amplify the response
Effector cells – short lived – attack the antigen and the pathogens that are making it
Memory Cells – long lived – bear receptors specific for the antigen
Clonal Selection – proliferation (making lots) of clone cells in response to an antigen
-Presenting of an antigen to a receptor leads to lots of cell division = thousands of cells to fight pathogen

30. Clonal Selection
Primary Immune Response- takes days (when you get sick)
invader attacks a body cell
antigens from invader bind to a B cell with the correct receptor
B cell proliferates (makes lots of copies of itself) and makes two types of cells (effector and memory)

31. Clonal Selection
Secondary Immune Response – takes 2-7 days (usually don’t get sick)
Individual is attacked by same invader at a later time
T and B memory cells recognize the antigen much faster and produce a stronger response (2-7 days)

33. E. Categories of Immune Responses
Humoral Response
involves most body cells
responds to antigens or pathogens circulating in the blood or lymph fluid
B cells produce plasma cells
Plasma cells release antibodies that bind to invading antigen
B cells produce memory cells for future immunity
Used for Extracellular pathogens

36. Cell Mediated Response
uses mostly T cells and responds to any nonself cell triggering the following events:

37. Cell Mediated Response
Antigen presenting cell stimulates Cytotoxic T cell
Cytotoxic T cell becomes activated
Secretes proteins to cause cell rupture and cell death
Used for Intracellular pathogens and cancer
Also makes memory T cells for future infection

40. Role of Antibodies Bind to antigen
Interfere with pathogen in different ways
Bind to pathogen and block it’s ability to enter host
Bind to toxins released by pathogen and neutralize them
Made it easier for macrophage to recognize invader
Use a membrane attack complex to make a hole in the membrane of the foreign object – cause it to swell and burst