1. External and Internal Defenses
Immune System Chapter 35
External and Internal
Defenses

2. I. External Defenses (all non-specific)
A) Skin…waterproof layer dead cells
B) Linings of body tubes/cavities
1) sticky mucus w/ lysozyme enzymes
2) ciliated cells in resp. tract
3) stomach acid & bile salts
4) urine & vaginal low pH
C) Neutral/beneficial bacteria population

3. II. Internal Defense Types
A. innate immunity =
present at birth, always present, all animals, non-specific
B. aquired/adaptive immunity =
activated by microbes/antigens
a) Require self-recognition
(membrane proteins)
b) only present in Vertebrates

4. III. Vocabulary
A. Antigens =any foreign molecule recognized by immune system
1) bacteria membrane proteins
2) parts of virus protein coat
3) oligosaccharides on transplanted cells

5. B. Phagocytes = cell that does phagocytosis
1. endocytosis to take in and digest organic materials
2. in immune system take in microbes
(virus/bacteria) & digest them

6. C. MHC = major histocompatibility molecules
1. cell surface proteins display antigens
2. two types
a. Class I MHC display foreign peptides synthesized within the cell (cancer/virus)
found on most body cells
b. Class II MHC display peptides broken off of microbes during phagocytosis
found on phagocytic cells & B cells

7. D. Helper–T cells 1. Type of white blood cell
2. Receptors bind to (antigens) displayed by MHC molecules
3. secretes signal molecules called cytokines
4. cytokines activate acquired immune system
a. B cells
b. cytotoxic T cells

9. IV. Blood Cells – all start in bone marrow
A) Leukocytes = White Blood Cells
1) Lymphocytes
a) B cells mature in bone marrow
b) T cells mature in thymus gland
2) Phagocytes (eosinophils, neutrophils,
macrophages, dendritic cells)

10. B) Erythrocytes = Red Blood Cells
1) anucleate in mammals
2) hemoglobin carries O2 and some CO2
3) flexible biconcave oval
4) form in bone marrow

11. I. Innate Immunity

12. A) Phagocytic cells (2 examples)
1) macrophages – largest
2) dendritic cells – activate acquired immunity
a) digest pathogen into pieces
b) bind pathogen pieces to MHC receptors*
c) display pathogen on cell membrane
d) attract helper T cells*
e) helper T cells activate acquired imm. resp.

13. B) Natural Killer Cells
1. NK cells vertebrate innate defense.
2. Attack virus infected cells and cancer cells
3. NOT MHC molecule receptors…just detects changes in cell membrane
4. Produce signal molecules that cause apoptosis

14. C) Antimicrobial Proteins
1) interferon ά and β
secreted by virus-infected cells
help neighboring cells inhibit viral reproduction
2) complement system = 30 serum proteins
a. microbe presence activates complement proteins
b. cascade of chem rxns lead to
c. microbe lysis
d. plays a role in inflammation
(complement syst also activated by acquired response)

15. 1) Mast cells release histamine signal mol.
D) Inflammation:
1) Mast cells release histamine signal mol.
due to Allergen, antigen or injury
2)Histamine signals capillaries to
a) dilate which lets out more
i. clotting elements (block spread of microbes)
ii. anti-microbial proteins (complement system)
iii. Phagocytes
b) produce signal molecules to attract phagocytes (macrophages)
Macrophages secrete cytokines that promote blood flow

16. Signal Molecules Review
Histamines –released by mast cells
- trigger capillaries to dilate
Chemokines – released by capillaries
- attract phagocytes
Cytokines -released by macrophage/neutrophils
- increase blood flow
-released by helper T
- activate acquired immune resp.
signal B-cells and cytotoxic-T cells

18. E) Systemic Response Widespread response Increased WBC production
Fever – facilitates phagocytosis
Septic shock – bacterial infection causes high fever low bp may cause death

19. http://highered. mheducation

20. II aquired/adaptive immunity
A) Humoral Response =
B cells make antibodies
B) Cell Mediated Response =
Cytotoxic T cells defends against:
infected cells
Cancer cells
Transplanted cells

21. Antibodies Proteins secreted by differentiated B-cells (plasma cells)
Bind to specific antigen
Also called Immunoglobulins (Ig)

22. Humoral Response = B cells put antibodies in fluid (humor)
1. B cell receptor binds to an antigen on microbe, pollen or transplanted cell
2. B cell takes in antigen and presents it on MHC II surface protein to attract helper T cells
3. Helper T binds to MHC-antigen complex and begins secreting cytokines
4. cytokines induce mitosis in B cell to produce
a. plasma cells
b. memory B-cells

24. Plasma cells make antibodies specific to the antigen that their parent B-cell bound
1.bind & clump viruses/bacteria
2. precipitate antigens dissolved in fluid
3. activate complement proteins
Memory B-cells stay in blood stream ready to become activated in secondary immune response.

25. Secondary Immune Response

26. Cell Mediated Response =fights cancer, infected cells, transplant cells
1. Class I MHC molecule displays antigens
that are synthesized inside affected cell
2. Cytotoxic Tcells bind to MHC-antigen complex
3. Binding makes cytotoxic Tcell secrete:
a. perforin
(protein, makes holes in membrane)
b. enzymes to digest the cell
c. signals to cause apoptosis

27. More on Helper T Cells Helper T cells Activate by
1. binding C-II MHC-antigen complex
on dendritic cells, macrophages, or B-cells
2. Makes cytokines to stimulate
a. cytotoxic T cells to become active
b. B cells to begin clonal selection…..
mitosis to produce plasma & memory cells

28. Helper T clonal selection
Activated helper T does mitosis
1 clone divides to make many activated helper T cells
The other divides to make memory helper T cells

30. Lymphocyte receptor diversity
1 million diff. B cells….10 million diff. T cells
When leukocytes differentiate into lymphocytes
1. Recombinase enzymes link 1 V gene
segment to 1 J gene segment
2. all receptors on that cell the same

32. Autoimmune disease
New lymphocytes are tested to be sure their receptors won’t bind to bodies own cells.
Failure to remove self-reactive cells = autoimmune disease