The Immune System Your 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.

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.

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  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. 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)

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. 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 a specific immune response –Vaccines –Natural exposure

The 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 move toward infection and damaged tissue –characterized by swelling, redness, and pain capillary wall extracellular 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. 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 cell T 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

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

Sterilization Process by which all living organisms and viruses are destroyed. Autoclave – Pressurized steam heat –15 lbs/sq. 254◦F for at least 15 minutes. –Explodes spore forming bacteria

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 carries genes for antibiotic resistance on a plasmid. A copy of the plasmid is transferred through conjugation. Resistance is quickly spread through many bacteria.

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 is stimulated 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 vaccine trigger an immune response, and memory B cells are made. 1 memory 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. 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. 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 cell dead T cell antibody activated B 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