Immunology Chapter Overview

Diseases and Immunity

• A pathogen is a disease-causing organism.
• Transmissible diseases are diseases where pathogens can be passed from one host to another.
• Pathogens are transmitted by direct contact (including blood and other body fluids) and indirectly (from contaminated surfaces, food, animals, and air).
• Body defenses include skin, hairs in the nose, mucus, stomach acid, and white blood cells.
• Factors important in controlling disease spread include clean water, hygienic food preparation, good personal hygiene, waste disposal, and sewage treatment.
• Active immunity involves antibody production in response to a pathogen or vaccination; each pathogen has unique antigens with specific shapes. Antibodies are proteins that bind to antigens, leading to pathogen destruction or marking for destruction by phagocytes. Active immunity is gained after a pathogen infection or vaccination, involving weakened pathogens or antigens to trigger an immune response and produce memory cells for long-term immunity.
• Passive immunity provides short-term defence against a pathogen through acquired antibodies from another individual (e.g., across the placenta, breast milk). Memory cells are not produced in passive immunity.
• Cholera is a disease caused by a bacterium transmitted in contaminated water. The bacteria produce a toxin causing chloride ion secretion into the small intestine and osmotic water movement. This leads to diarrhea, dehydration, and ion loss.
• Chemical barriers in the body help trap or destroy pathogens.
• Mucus traps bacteria entering the respiratory system.
• Stomach acid kills pathogens entering the digestive system.
• Skin, nose hairs, and mucus act as mechanical barriers blocking pathogen entry.
• Cellular barriers are components of the immune system which take part in combating pathogens and disease.
• Lymphocytes produce antibodies.
• Phagocytes engulf and digest pathogenic cells.

Phagocytosis

• Phagocytosis is the process by which phagocytes digest pathogens.
• A phagocyte extends itself to engulf a pathogen.
• Enzymes digest the pathogen inside the phagocyte.

Antigens and Antibodies

• All cells have proteins and other substances projecting from their cell membrane called antigens, which are specific to cell type.
• Lymphocytes can identify foreign antigens and create complementary antibodies to bind to and neutralize these antigens.
• Antibodies cause agglutination (clumping) of antigens, preventing their movement and signaling phagocytes for destruction

Active Immunity

• Lymphocytes create memory cells that remain in the blood post-infection, allowing rapid antibody production if the same pathogen is encountered again.
• Active immunity results from infection with a pathogen or vaccination.
• Antibody production and memory cell development is active immunity.

Passive Immunity

• Passive immunity is a short-term defense against a pathogen using antibodies acquired from another source.
• Antibodies are introduced from another source (e.g., mother to infant via breast milk).
• Passive immunity is fast-acting and provides short-term protection.

Vaccination

• Vaccinations use harmless or altered pathogens (or their antigens) to create an immune response without causing illness.
• Vaccination creates memory cells for long-lasting immunity.
• The level of protection in a population depends on the proportion of people vaccinated.

How Does Vaccination Work?

• Vaccines introduce weakened pathogens or antigens triggering an immune response.
• Antibodies target the pathogen via memory cells.
• Memory cells allow rapid antibody production upon subsequent encounters.

How Does Vaccination Control the Spread of Disease?

• High vaccination rates create herd immunity, limiting pathogen spread as there are fewer susceptibles.
• Lower vaccination rates and a prevalence of infectious diseases lead to higher infection rates and mortality.

Autoimmune Diseases

• Some diseases result from the immune system attacking healthy body cells (e.g., Type 1 diabetes).

Controlling the Spread of Disease

• Hygienic food preparation involves proper food handling procedures, including cooking and temperature control.
• Good personal hygiene includes handwashing with soap, using tissues to cover coughs and sneezes, and proper restroom hygiene.
• Waste disposal involves proper waste management and the avoidance of waste contamination of the environment or food sources to avoid disease.
• Sewage treatment involves methods to remove solid waste and pathogens from waste prior to disposal into the environment.
• Clean water supplies involve treating water with disinfectants or chemical treatment to remove disease-causing microbes.

How Does Vibrio Cholerae Cause Diarrhea

• Vibrio cholerae bacteria attach to and spread inside the small intestine.
• Bacteria produce a toxin releasing chloride ions into the intestine
• This lowers the water potential, drawing water from the intestinal wall into the gut.
• This results in watery diarrhea.

Important Terminology

• A pathogen is a disease-causing organism.
• Antibodies are proteins that bind to antigens.
• Antigens are substances on the surface of cells that trigger an immune response.
• Phagocytes are cells that engulf and destroy pathogens.
• Active immunity is immunity acquired after exposure to a pathogen or vaccination.
• Passive immunity is immunity acquired by exposure to antibodies from another source.
• Vaccination is the process of introducing a harmless form of a pathogen to induce immunity.