Infectious Disease & The Immune System

Disease Disease – any change, other than injury, that disrupts the normal functions of the body Some diseases are produced by agents (bacteria, viruses, etc.), some are environmental and some are inherited Pathogens – disease-causing agents; “sickness-makers”

Germ Theory of Disease Robert Koch ( ) – Germ Theory –A specific microorganism causes a specific disease

Koch’s Postulates 1. The specific agent must be associated with every case of the disease. 2. The agent must be isolated from a diseased host and grown in culture.

3. When the culture-grown agent is introduced into a healthy susceptible host, the agent must cause the same disease. 4. The same agent must again be isolated from the infected experimental host.

Agents of Disease Viruses (Common Cold, Influenza (flu)) Bacteria (Strep, Botulism, Anthrax) Protists (Plasmodium (causes Malaria, Amebic dysentery) Worms (Tapeworms, Hookworms) Fungi (Ringworm, Athlete’s Foot)

Emerging Infectious Diseases Emerging diseases are those that have recently appeared within a population, or whose incidence or geographic range is increasing rapidly.

Diseases can emerge or re- emerge due to: –appearance of a previously unknown agent. –evolution of a new infectious agent. –spread of an infectious agent to a new host.

–acquisition of resistance to anti-microbial drugs. –spread of an infectious agent to new locations. –deliberate introduction into a population.

How are Diseases Spread Physical Contact –Direct – Touching –Indirect – Sneezing or Coughing Contaminated Food & Water Infected Animals – vectors that carry diseases like mosquitoes

Fighting Infectious Diseases Antibiotics – compounds that kill bacteria –Only work on bacterial infections, no effect on viruses – –Fleming (1928) discovered penicillin (Penicillium mold on bacterial plate)

Vaccines are to prevent infections Jenner made smallpox vaccine (1796) from cowpox blisters on a milk maid (given to his son) Salk (1952) made polio vaccine by using formaldehyde to kill virus then injected himself

Over-the-Counter Drugs –Can treat the symptoms of the disease and make you feel better, but they do not treat the cause of the disease – you need your Immune System for that

The Immune System Body’s main defense against pathogens It recognizes, attacks, destroys and “remembers” each type of pathogen that enters the body Does this by producing specialized cells that inactivate pathogens – there is a specific cell produced for each pathogen

Two Categories of Defense 1. Nonspecific Defenses –Guard against the infections by keeping most things out of the body 2. Specific Defenses –Track down harmful pathogens that have broken through the body’s nonspecific defenses

Nonspecific Defenses First Line of defense: –Helps keep pathogens out of the body –Most important nonspecific defense is the skin –Mucus, sweat and tears also help in this process

Second line of defense: –Inflammatory response –White blood cells (phagocytes) near the wound engulf the pathogen –A fever may develop to slow down or stop the growth of pathogens

Specific Defenses If a pathogen can get past the body’s nonspecific defenses, then the immune system reacts with a series of specific defenses to attack the invader

A substance that triggers this response is known as an antigen (Viruses, bacteria and other pathogens serve as antigens that trigger the immune system response)

The cells of the immune system that recognize specific antigens are two types of lymphocytes: –B lymphocytes (B cells) –T lymphocytes (T cells)

B cells provide immunity against antigens and pathogens in the body fluids (humoral immunity) –B cells divide rapidly and produce lots of plasma cells and memory B cells –Plasma cells release antibodies (proteins that recognize and bind to antigens) B lymphocytes (B cells)

Once the body has been exposed to a pathogen, the body maintains the ability to produce those specific antibodies again at any time (memory B cells)

Picture of an Antibody Antibodies are shaped like a Y Shapes of the binding sites are different on each antibody in order to recognize a large variety of antigens

T lymphocytes (T cells) Cell- Mediated immunity: When the body’s own cells are infected with a virus or become cancerous, antibodies alone cannot destroy them This is where T cells are needed to help fight these kind of infections

T cells divide and differentiate into killer T cells, helper T cells, suppressor T cells, and memory T cells Killer T cells do just that to the pathogen!

Immunity 1. Natural Exposure to an antigen – –You have a disease and fight the infection off 2. Deliberate Exposure – –Vaccination – injection of a weakened or mild form of a pathogen; used today to prevent more than 20 serious human diseases

Immune System Disorders Allergies – overreaction to dust, pollen, mold, bee stings, etc. Asthma – chronic respiratory disease in which the air passages become narrower than normal

Autoimmune Diseases – when the immune system makes a mistake and attacks the body’s own cells; ex. Type I diabetes and Multiple Sclerosis (MS)

AIDS (Auto Immune Deficiency Syndrome) Results from a viral infection (HIV) that destroys the T cells of the immune system Leaves the body with no protection against other pathogens

HIV can be spread by sexual contact, sharing needles during drug use, contact with blood or blood products of an infected person & from infected mother to child No cure at this time, but there are many drugs that can prolong the life of someone with HIV/AIDS

Human Immunodeficiency Virus. HIV-1 virions can be seen on surface of lymphocytes.

Immune System Video Clip