The Immune System and Diseases

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

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

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

Defenses Against Infection 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

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.

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.

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.

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.

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.

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

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