V. Biological Injury Continued Viruses

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

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

Influenza Virus Diagram ©http://www. ifpma

West Nile Virus: a surface-shaded image of the West Nile virus particle produced by Purdue University biologists using cryoelectron microscopy. ©http://www.newsroom.ucr.edu/images/releases/1033_1.jpg

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

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

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

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

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

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

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)

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

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

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

©http://www.cdc.gov/ncidod/dvbid/dengue/images/map-distribution-2005_500.jpg

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

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)

HIV Virus Illustration ©http://www. vircolab

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

©http://www.biology.duke.edu/cibl/exercises/virus_tracker_fig1.gif

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

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

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)

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

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

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

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

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

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

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:

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 )

©http://library. thinkquest ©http://library.thinkquest.org/03oct/00520/gallery/photos/HelperTcellandBcell.jpg

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

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

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

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

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

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

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

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