1. V. Biological Injury Continued
Viruses

2. Viruses
Virus: an extremely small structure consisting of only nucleic acid and protein
Cannot live on its own
Invade host cells, insert their own DNA into host’s DNA, and produce more viral DNA
Infect more cells by exocytosis or breaking the host’s cell membrane

3. Virus Structure ©http://www.armageddononline.org/image/virus2.JPG

4. Influenza Virus Diagram ©http://www. ifpma

5. West Nile Virus: a surface-shaded image of the West Nile virus particle produced by Purdue University biologists using cryoelectron microscopy. ©

6. Viruses Three major forms of viruses: DNA Viruses RNA Viruses
Retro Viruses

7. DNA Viruses The core genetic material is DNA
Make more viral DNA by entering a host cell and taking over its organelles
Do not mutate easily

8. DNA Viruses
Examples:
Small Pox
Herpes
Epstein-Barr
Hepatitis B
HPV

9. Epstein-Barr Virus Illustration ©http://www. spaceflight. esa

10. Small Pox Virus ©http://gtresearchnews.gatech.edu/images/smallpox1.gif

11. Herpes Virus ©http://images. google. com/imgres. imgurl=http://www

12. RNA Viruses The core genetic material is RNA Two Classifications:
Positive—Stranded (take over the host cell just as they are)
Negative—Stranded (must make a complimentary RNA strand before taking over the host cell)

13. Polio Virus ©http://www.learnodes.com/images07/09/poliovirus.jpg

14. 100 Polio Viruses ©http://www. aminol-uk

15. Yellow Fever Virus ©http://www. turnerlearning. com/tbs/plague/yellow

16. ©

17. Retroviruses Genes are carried in a single positive strand of RNA
Once inside the cell, the virus creates a double-strand viral RNA
The double-strand viral RNA inserts itself into the host cell’s DNA

18. This affects not only protein synthesis, but also cell reproduction
When the cell divides, the viral genes are passed on to the daughter cells
Example: HIV (human immunodeficiency virus)

19. HIV Virus Illustration ©http://www. vircolab

20. HIV particles and a white blood cell ©http://www. wellesley

21. ©

22. How do Viral Infections Occur. ©http://images. healthcentersonline

23. Immune Response Review
The cells of the immune system are called leukocytes (also known as white blood cells)
Two basic types of leukocytes:
Phagocytes: engulf and destroy foreign bodies (common defense for bacterial infections)
Neutrophils
Monocytes
Macrophage

24. Two types of lymphocytes:
Lymphocytes: cells that allow the body to remember and recognize previous invaders and help to destroy them (common defense for viral infections)
Two types of lymphocytes:
T lymphocytes (from the thymus)
B lymphocytes (from bone marrow)

25. Immune Response to Viruses
Viruses are small enough to enter cells
When you are healthy and do not have an active virus, some of the monocytes leave your capillaries and sit under the epithelial cells
Now called macrophages

26. Monocyte to Macrophage ©http://www. brookline-design

27. MACROPHAGES Engulf and digest debris that moves into the bloodstream
Wait for viruses to leave a cell and try to enter new cells

28. Macrophage
When this happens, macrophages release lymphokines—signaling molecules—to other white blood cells
Remember, lymphokines are interleukins– protein molecules that act as signals to beckon more wbc

29. Mouse Macrophage Attacking Two Particles ©http://content. answers

30. HELPER T CELLS Macrophages signal helper-T cells
Produced in bone marrow but move to and mature in the thymus gland (located at the base of the neck, aids in the production of lymphocytes (wbc))
Helper T cells are the commander in chief of the immune system

31. Helper T Cells
Identify viruses as foreign, rush to the spleen and lymph nodes to stimulate the production of other infection fighting cells
Signal other wbc to fight the pathogen:

32. Accomplish this by:
Secreting interleukin 2: stimulates killer T cells to respond (another type of wbc)
Secreting B-cell growth factor (interleukin 6—stimulates the growth and differentiation of B-cells—yet another wbc )

33. ©http://library. thinkquest©

34. Killer T Cells Summoned by the helper T cells
These find cells that have virus protein coats embedded in them (foreign antigens) and destroy the cell

35. Killer T Cells
Destroy the cell by secreting perforins and lymphotoxins
Sacrifice one cell for the good of many
Can be problematic in some types of cells
Ex. Liver cells—some do not mitose

36. Killer T Cell with Viral Particles ©http://images. google. com/imgres

37. Memory T Cells
Once a virus is under control, these cells remain in the lymph nodes for many years
Should the same pathogen (virus) enter the body, these cells produce clones of the T cells resulting in a rapid response

38. B-Lymphocytes Killer T cells stimulate B-lymphocyte production
B-lymphocytes produce antibodies
Antibodies are specialized proteins that lock onto specific antigens (lock and key mechanism)
Y shaped antibodies prohibit viruses from entering cells

40. Antibodies cannot usually destroy antigens (viruses) by themselves; that is the job of the killer T cells
Antibodies can neutralize some antigens

41. B Memory Cells
A certain population of B-lymphocytes become B memory cells
They move to the spleen or lymph nodes and produce a small amount of antibodies for years
If the antigen (virus) shows up again, the B memory cells multiply and produce more antibodies

43. Suppressor T Cells Fourth type of T cell
After the infection is controlled, these cell slow down or stop the activities of the other T cells and B cells