The Immune SystemThe Immune SystemYour Body’s Defense System

• Germ theory proposes that microorganisms cause diseases.– proposed by Louis Pasteur– led to rapid advances in understanding disease

Germ theory states that microscopic particles cause certain diseases. Germ theory states that microscopic particles cause certain diseases.

Disease-causing agents are called pathogens.

Koch’s postulates support the theory.

Koch’s postulates:Four conditions linking pathogen to disease

• Pathogen thought to cause disease must be present in every case the disease is found.

• Pathogen must be isolated and grown outside the body in a pure, uncontaminated, culture.

• Healthy organisms infected with pure culture must develop disease.

• Pathogen must be re-isolated and cultured from newly infected host organism and must be identical to original pathogen.

Antiseptic technique, sanitation principles, vaccines, and antibiotics significantly impacted human population growth

• Bacteria are single-celled organisms. – cause illness by

destroying cells – release toxic

chemicals

There are different types of pathogens. There are different types of pathogens.

Viruses are genetic material surrounded by a protein coat.

– force host cells to make more viruses

– very small

Fungi can be multicellular or single-celled.

– take nutrients from host cells–occur in warm and damp places

Protozoa are single-celled organisms.

– use host cells to complete their life cycles– take nutrients from host cell

Parasites are multicellular organisms.

– grow and feed on a host – possibly kill the host

• Different pathogen cause common infectious diseases.

Pathogens can enter the body in different ways.Pathogens can enter the body in different ways.• Pathogens can be transferred by direct or indirect

contact.• Indirect contact does not require touching an infected

individual. touching an infected surface

breathing in infected air Fomites

• Direct contact requires touching an infected individual. Includes: Kissing, sexual intercourse, hand

shaking

Vectors carry a pathogen and transmit it into healthy cells.

Deer tick

• The immune system is the body system that fights off infection and pathogens.

• Many other tissues and systems help the immune system.

• Skin is a physical barrier to infection.• Mucous membranes trap pathogens entering

the body.• The circulatory system transports immune

cells.

The immune systems consists of organs, cells, and molecules that fight infections.

Cells and proteins fight the body’s infections.Cells and proteins fight the body’s infections.

• White blood cells attack infections inside the body.

• Phagocytes engulf and destroy pathogens.

• T cells destroy infected cells.

• B cells produce antibodies.

Leukocyte Cells (White Blood Cells / WBCs)Leukocyte Cells (White Blood Cells / WBCs)

Three types of proteins fight off invading pathogens.

– Complement proteins weaken pathogen membranes.

– Antibodies make pathogens ineffective.

– Interferons prevent viruses from infecting healthy cells.

antibody

pathogens

Immunity prevents a person from getting sick from a pathogen.

Immunity prevents a person from getting sick from a pathogen.• In all immunity, pathogens are destroyed before

you get sick.• Passive immunity occurs without

an immune response.– Mother’s milk– Genetics

• Active immunity occurs after aspecific immune response– Vaccines– Natural exposure

The immune system has many responses to pathogens and

foreign cells.

The immune system has many responses to pathogens and

foreign cells.

Many body systems work to produce nonspecific responses. Many body systems work to produce nonspecific responses.

• Nonspecific responses are the same for every pathogen.

• In inflammation, blood vessels become leaky.–white blood cells move

toward infection anddamaged tissue

– characterized by swelling, redness, and pain

capillary wallextracellular space

white blood cell

In fever, body temperature increases.

– High fevers can cause seizure, brain damage, and even death.

– Low fevers stimulate white blood cells to mature.

Immune Response

Cells of the immune system produce specific responses.Cells of the immune system produce specific responses.

• Specific immune responses begin with the detection of antigens.–Antigens are surface

proteins on pathogens.–Each pathogen has a

different antigen.

virus

antigens

pathogen

antigens

T cell

receptors activated T cells

antigens

memory T cells

There are two specific immune responses.

– Cellular immunity uses T cells to destroy infected body cells.

There are two specific immune responses.

– Humoral immunity uses B cells to produce antibodies.

memory B cells

activated B cells

antibodies

B cell

T cell

pathogen

Both responses produce memory cells.

– specialized T and B cells– provide acquired (active) immunity

B cellT cell

The immune system rejects foreign tissues. The immune system rejects foreign tissues.

• Tissue rejection occurs in organ or tissue transplants.

• Tissue rejection is the result of an immune response.– immune system detects protein markers on the

donor tissue–makes antibodies against the donor’s tissue

Many methods are used to control pathogens.Many methods are used to control pathogens.

• Antibiotics and antiseptics cause pathogens to burst.

Living in a clean environment and building immunity help keep a person healthy.

Antiseptics and disinfectants kill pathogens outside of the body.

Do not target specific pathogen• Antiseptics – Bacteriostatic - reduce number of

pathogens and prevent reproduction.• Safe for use on human skin/tissue.• e.g. Isopropyl alcohol, Iodine

• Disinfectants – Bactericidal – kill most bacteria and destroy most viruses.• Used on surfaces• e.g. Bleach, Cidex

SterilizationSterilization

• Process by which all living organisms and viruses are destroyed.

• Autoclave – Pressurized steam heat–15 lbs/sq. in. @ 254◦F

for at least 15 minutes.–Explodes spore forming

bacteria

Antibiotics kill pathogens inside the body.Antibiotics kill pathogens inside the body.

– target one specific bacterium or fungus– not effective against viruses

• Antibiotic resistance can cause medicines to become ineffective.

–Some bacteria in a population have genes that make them immune to antibiotics.

–These bacteria spread the gene, making the antibiotics useless.

A bacterium carriesgenes for antibioticresistance on a plasmid.

A copy of the plasmid is transferredthrough conjugation.

Resistance is quicklyspread throughmany bacteria.

Vaccines artificially produce acquired immunity.Vaccines artificially produce acquired immunity.

• Vaccines also control pathogens and disease.–given to prevent illness– contain the antigen of a weakened pathogen–Controlled exposure

Vaccination provides immunity.

– stimulates a specific immune response

– allows immune system to respond quickly to infection

– causes memory cells to be produced

– has such a fast response, a person will not get sick

A memory B cell isstimulated when the real pathogen binds to it.

2

The B cell quickly activates and makes antibodies that fight the pathogens before you get sick.

3

Antigens in a vaccinetrigger an immune response, and memory B cells are made.

1memory B cells

An overactive immune system can make the body very unhealthy.

Allergies occur when the immune system responds to harmless antigens.• Allergies are caused by allergens.

– Allergens are antigens that cause an allergic reaction.

– Allergens cause inflammation responses.

– food, e.g. peanuts, milk, wheat, etc.– airborne, e.g. pollen, dust mite feces, mold, etc.– chemical, e.g. nickel, medicine, bee stings, etc.

Allergens can cause anaphylaxis.

–Anaphylaxis is an extreme inflammation response.

–Blood vessels and airways become too porous.

– If not treated immediately, anaphylaxis can cause death.

In autoimmune diseases, white blood cells attack the body’s healthy cells.

In autoimmune diseases, white blood cells attack the body’s healthy cells.

• Autoimmune diseases are failures of the immune system.– White blood cells cannot

recognize healthy cells.– White blood cells attack

healthy body cells.– Tissues fail because of

attack.

• There are over 60 autoimmune diseases.

– characterized by immature white blood cells

– causes weakened immune system

• Leukemia is cancer of the bone marrow.

When the immune system is weakened, the body cannot fight off disease.

HIV targets the immune system.HIV targets the immune system.

• The human immunodeficiency virus (HIV) is a retrovirus.

– attacks and weakens the immune system

– is transmitted by mixing infected blood with a bodily fluid

HIV infection leads to AIDS.

HIV

T celldeadT cell

antibody

activatedB cell

– HIV reproduces in and destroys T cells.– The body cannot replace T cells fast enough.– T cells cannot help in immune responses.

AIDS is acquired immune deficiency syndrome.

– several opportunistic infections– very low amount of T cells