1. An Introduction to the IMMUNE SYSTEM
Disease and Pathogens
An Introduction to the IMMUNE SYSTEM

2. What causes disease?
Microbes: microscopic living organisms such as bacteria, protists, and many fungi, and viruses
Some microbes are pathogens, a term derived from Greek words meaning “to produce disease”
Pathogens reproduce and seek new hosts
Most microbial diseases, such as cholera, measles, plague, tetanus, and chicken pox, have been with humans for thousands of years
Viruses in the news include
HIV
Ebola virus
West Nile virus
Swine (H1N1) flu
Measles

3. Not all microbes are pathogens…BUT…
Some common bacteria have deadly strains
The intestinal bacterium Escherichia coli is usually harmless, indeed beneficial, because it produces vitamin K in our large intestines
However, one strain, called O157:H7, usually acquired by eating undercooked ground beef, causes food poisoning, sometimes with fatal consequences
Staphylococcus aureus bacteria (“staph”) occur frequently on the skin and in the nasal passages, but some strains cause fatal toxic shock syndrome or prolonged infections if they penetrate through the skin or mucous membranes
Methicillin Resistant Staphylococcus aureus (MRSA) and Mycobacterium tuberculosis (which causes TB) have become resistant to most antibiotics

4. How Does the Body Defend Against Pathogens?
We have three major lines of defense: nonspecific external barriers, nonspecific internal defenses, and specific internal defenses
Nonspecific external barriers prevent most disease-causing microbes from entering the body
The anatomical structures include skin and cilia
Secretions include tears, saliva, and mucus
Nonspecific internal defenses are collectively called the innate immune response and swing into action if external barriers are breached
Some white blood cells engulf foreign particles or destroy infected cells
Chemicals released by damaged body cells and proteins released by white blood cells trigger inflammation and fever
Specific internal defenses, the final line of defense, comprise the adaptive immune response, in which immune cells selectively destroy the specific invading toxin or microbe and then “remember” the invader, allowing a faster response if it reappears in the future

5. 5 Nonspecific External Barriers Innate Immune Response
skin, mucous membranes
If these barriers are penetrated, the body responds with
Innate Immune Response
phagocytic and natural killer cells, inflammation, fever
If the innate immune response is insufficient, the body responds with
Adaptive Immune Response
cell-mediated immunity, humoral immunity 5