The Immune System

Infectious Disease

• Pathogens are disease-causing “invaders”• Infectious diseases can be spread by contact with infected people,

animals, water, or food.• Four ways to transmit infectious diseases (with examples):

Direct contact: shaking hands or sharing drinks or bodily fluids with an infected person

Indirect contact: being near an infected person who sneezes without covering his or her mouth

Water and food: eating foods infected with certain bacteria, ex, Salmonella. Drinking water infected with E.coli bacteria can also result in serious illness.

Animal bites: being bitten by an animal carrying rabies

Immune System: First Line of Defence

• The skin and the linings of all internal body systems. Sweat and oil are acidic.

• Gastric juice is acidic, and can destroy pathogens.

Second Line of Defence: Innate Immune Response

• Quick and general• Usually fight bacteria and

some viruses.• First action is a flow of fluid,

cells, and dissolved substances to the infection site.

• Fever, inflammation and redness occurs.

• A type of white blood cells called phagocytes will increase in number.

• The phagocytes engulf and swallow the pathogens.

Acquired Immune Response• Highly specific attack on a pathogen, or antigen.• An antigen is any substance the body cannot recognize, it is a

non-living particle or substance• Your body uses WBC’s called B cells and T cells to respond.• The process can take up to a week.• B cells recognize antigens and produce specific particles, called

antibodies to fight them. • Antibodies attach and destroy antigens and pathogens carrying

antigens.

• T cells: helper T cells recognizes an antigen or pathogen and activates B cells.

• T cells: killer T cells work independently and destroy antigens or pathogens.

• All acquired immune responses help give you active immunity. Your body remembers which antibodies should be used to attack a pathogen that it has seen before.

• Memory B cells store the new antibodies

Factors Affecting the Immune System

Vaccinations• Vaccines: a special version of

an antigen that gives you immunity against a disease.

• Vaccines are like weakened forms of a disease, they stimulate your immune system to create antibodies against the disease.

• These antibodies are reactivated to fight the antigen if it enters your body.

• Some vaccines require booster shots.

• All grade 9 students receive booster shots for tetanus, diptheria, and pertussis.

Disorders of the Immune System• Allergies: an unusually high

sensitivity to some substance. • Something that causes an

allergic reaction is an allergen.• The allergen acts as an antigen

for you, and your immune system kicks in.

• The symptoms of an allergy are cause by a substance called histamine, that your body releases.

• A severe reaction to an allergen is called anaphylactic shock, and can result in breathing difficulty, swelling, and sometimes death.

Acquired Immunodeficiency Syndrome (AIDS)• AIDS is an infection of the immune

system.• AIDS is caused by the human

immunodeficiency virus (HIV).• HIV attacks the immune system itself, and

destroys it by infecting helper T cells.• The immune system becomes unable to

defend against pathogens or antigens.• A person infected with HIV can die from

other, less serious infections.• AIDS has resulted in the death of more

than 11 million people, and currently affects more than 40 million people.

• HIV is transmitted in two body fluids, semen and blood.

• People are infected by unsafe behaviour, such as having sex with a person who has HIV without using a condom, or sharing contaminated needles.

• HIV cannot be transmitted by casual contact such as shaking hands.