Unit 31 Immune System

31.1 Pathogens and Human Illness

KEY CONCEPTGerms cause many diseases in humans.


Germ theory states that microscopic particles cause certain diseases.

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


• Disease-causing agents are called pathogens.

• Koch’s postulates support the theory.


There are different types of pathogens.

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

cells – release toxic chemicals


• 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 be transferred by direct or indirect contact.• Indirect contact does not require touching an infected

individual.

– touching an infected surface– breathing in infected air


• Vectors carry a pathogen and transmit it into healthy cells.

• Direct contact requires touching an infected individual. Includes: – kissing– sexual intercourse – hand shaking

tick

31.2 Immune System

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

31.2 Immune System

Many body systems protect you from pathogens.

• 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.

31.2 Immune System

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.

31.2 Immune System

• 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

31.2 Immune System

Immunity prevents a person from getting sick from a pathogen.

• In all immunity, pathogens are destroyed before you get sick.

• Passive immunity occurs withoutan immune response.– mother’s milk– genetics

• Active immunity occurs after aspecific immune response

31.3 Immune Responses

KEY CONCEPTThe immune system has many responses to pathogens and foreign cells.


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 movetoward 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.


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.

• 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

31.4 Immunity and Technology

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


Many methods are used to control pathogens.

• Antibiotics and antiseptics cause pathogens to burst.


• Antiseptics kill pathogens outside of the body.– do not target specific pathogens– examples include vinegar and soap

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


• 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

31.5 Overreactions of the Immune System

KEY CONCEPTAn overactive immune system can make the body very unhealthy.


Allergies occur when the immune system responds to harmless antigens.

• An allergy is an response to a harmless antigen.• Allergies are caused by allergens.

– Allergens are antigens that cause an allergic reaction.– Allergens cause inflammation responses.


• There are many different allergens. – 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.

• 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.

31.6 Diseases that Weaken the Immune System

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


Leukemia is characterized by abnormal white blood cells.

– characterized by immature white blood cells – causes weakened immune system

• Leukemia is cancer of the bone marrow.


• Leukemia leads to opportunistic infections.– occur because white blood cells cannot fight infections– if immune system were healthy, would fight these

infections


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