The Immune System and Diseases

1. The Immune System and Diseases

2. Infectious diseases • can be caused by viruses, bacteria, fungi, “protists”, and parasites. • Except for parasites, most of these disease-causing microorganisms are called pathogens. • Bacteria Characteristics: break down the tissues of an infected organism for food, or release toxins that interfere with normal activity in the host • Diseases Caused: streptococcus infections, diphtheria, botulism, anthrax Mycobacterium causes tuberculosis

3. Viruses • Characteristics: nonliving, replicate by inserting their genetic material into a host cell and taking over many of the host cell’s functions • Diseases Caused: common cold, influenza, chickenpox, warts • Influenza Virus, Strain taken from a Beijing 1993 epidemic

4. Any disease that can be transmitted from animals to humans is called a zoonosis (plural: zoonoses). Mad cow disease, severe acute respiratory syndrome (SARS), West Nile virus, Lyme disease, Ebola, and bird flu are all zoonoses. • Transmission can occur in various ways. • Sometimes an animal carries, or transfers, zoonotic diseases from an animal host to a human host. These carriers, called vectors, transport the pathogen but usually do not get sick themselves. • infection may occur when a person is bitten by an infected animal, consumes the meat of an infected animal, or comes in close contact with an infected animal’s wastes or secretions

5. Defenses AgainstInfection • Nonspecific Defenses • skin, tears and other secretions, the inflammatory response, interferons, and fever • First Line of Defense • Skin - Very few pathogens can penetrate the layers of dead cells that form the skin’s surface • Pathogens could easily enter your body through your mouth, nose, and eyes • saliva, mucus, and tears contain lysozyme, an enzyme that breaks down bacterial cell walls. Mucus in your nose and throat traps pathogens. Then, cilia push the mucous-trapped pathogens away from your lungs. • Stomach secretions destroy many pathogens that are swallowed

6. Second Line of Defense • inflammation -areas become red and painful, or inflamed. • Pathogens stimulate cells called mast cells to release chemicals known as histamines. Histamines increase the flow of blood and fluids to the affected area. This causes the area to swell. • White blood called phagocytes move from blood vessels into infected tissues and engulf and destroy bacteria. • All this activity around a wound may cause a local rise in temperature.

7. When viruses infect body cells, certain host cells produce Interferons- proteins that “interfere” with the synthesis of viral proteins. • The immune system also releases chemicals producing a fever. • Increased body temperature • slow down or stop the growth of some pathogens. • speeds up several parts of the immune response.

8. Specific Defenses • The immune system’s specific defenses distinguish between “self” and “other,” and they inactivate or kill any foreign substance or cell that enters the body.

9. A healthy immune system recognizes all cells and proteins that belong in the body, and treats these cells and proteins as “self.” • Foreign invaders – are specifically recognized, responded to, and remembered by the immune response.

10. Specific immune defenses are triggered by molecules called antigens. • Antigen -any foreign substance that can stimulate an immune response. • located on the outer surfaces of bacteria, viruses, and parasites. • Cause the production of proteins called antibodies • Antibodies -tag antigens for destruction by immune cells. • may be attached to particular immune cells • may be free-floating in plasma. • The shape of each type of antibody allows it to bind to one specific antigen.

11. The main working cells of the immune response are B lymphocytes (B cells) and T lymphocytes (T cells). • B cells • produced in, and mature in, red bone marrow. • B cells, with their embedded antibodies, discover antigens in body fluids. • T cells • produced in the bone marrow but mature in the thymus • must be presented with an antigen by infected body cells or immune cells that have encountered antigens. • Both- When mature, travel to lymph nodes and the spleen, where they will encounter antigens

12. Two styles of immune response- • humoral immunity and cell-mediated immunity. • humoral immunity • depends on the action of antibodies that circulate in the blood and lymph. • cell-mediated immunity • depends on the action of macrophages and several types of T cells