CHAPTER 24 The Immune System

Pathogens Disease causing agents such as bacteria, viruses, fungi, protozoans, and other parasites. ( NOT all microorganisms are pathogens)

Transmission of disease Pathogens can be transmitted to a host from reservoirs in four main ways: by direct contact, by an object, through the air, or by an intermediate organism called a vector.

Immune System Bodies primary defense against pathogens Three cooperative lines of defense have evolved to counter these threats. – Two of these are nonspecific - that is, they do not distinguish one infectious agent from another.

1st line: Physical Barriers non-specific defense external barriers – skin & mucus membranes – excretions sweat stomach acid tears mucus saliva – “lick your wounds” Lining of trachea: ciliated cells & mucus secreting cells

2nd: Generalist, broad range patrols Patrolling white blood cells – attack invaders that get through the skin recognize invader by reading antigen – surface name tag – phagocyte cells macrophages “big eaters” Macrophage “eating” bacteria

Lymph system Production of white blood cells & traps “foreign” invaders 2nd “circulatory” system lymph node lymph vessels (intertwined amongst blood vessels)

The lymphatic system becomes a crucial battleground during infection a network of lymphatic vessels and organs – It returns tissue fluid to the circulatory system – It fights infections Lymph nodes are key sites for fighting infection – They are packed with lymphocytes and macrophages

Phagocytes Macrophages wander in the interstitial fluid – They “eat” any bacteria and virus-infected cells they encounter

Phagocytes yeast macrophage bacteria white blood cells that eat

Antimicrobial Proteins Interferons: acts in warning other cells of a viral invasion Complement: help attract phagocytes to foreign cells and help destroy foreign cells

Natural Killer cells A type of white blood cell that destroy the body's own infected cells, may attack cells that form tumors

The inflammatory response mobilizes nonspecific defense forces Tissue damage triggers the inflammatory response ( redness, swelling, warmth, pus) injured cells release chemical signals histamines – increases blood flow – brings more white blood cells to fight bacteria – brings more red blood cells & clotting factors to repair The inflammatory response can – disinfect tissues – limit further infection

Fever When a local response is not enough – full body response to infection – raises body temperature – higher temperature helps in defense slows growth of germs helps macrophages speeds up repair of tissues

SPECIFIC IMMUNITY~ 3 rd line of defense IMMUNE RESPONSE a recognition system that distinguishes “self” from “non-self” responds to foreign molecules called antigens Stimulates the body to make antibodies: specific defensive proteins which help to counter antigens in various ways

How are invaders recognized? Antigens – chemical name tags on the surface of every cell “self” vs. “invader” disease-causing bacteria disease-causing virus one of your own cells antigens say: “I belong here” antigens say: “I am an invader”

Immunity=protection afforded to an organism by previous exposure to an antigen 2 types: 1.Active: long term, conferred by actual encounter with infection ( naturally acquired ) or vaccination * (artificially acquired) * vaccine~ substance consisting of weakened, dead,,or parts of pathogen or antigen that when injected, stimulates the immune system

Immunity 2. Passive: short term, antibodies passed on, not stimulated by antigens, acquired naturally by placenta or breast milk or artificially acquired by a shot

Immune Response ~ 3 rd line of defense Governed by 2 different parts of the immune system 1. Humoral Immunity: results in the production of antibodies 2. Cell-mediated Immunity: defensive activities are carried out by specialized cells circulating around the body

Lymphocytes ~type of white blood cell that carry out the immune response Two kinds – B cells secrete antibodies that attack antigens (humoral immunity) – T cells attack cells infected with pathogens (cell-mediated immunity) B lymphocyte

The initial immune response results in a type of “memory ” primary immune response produces memory cells – These cells may confer lifelong immunity When memory cells are activated by subsequent exposure to an antigen, they mount a more rapid and massive secondary immune response

Humoral Immune Response Triggered by a specific antigen, a B cell differentiates into a plasma cell -The plasma cell secretes antibodies

Antibodies are the weapons of humoral immunity An antibody molecule has antigen-binding sites specific to the antigen Do not posses the power to destroy antigens directly, tag and mark them for destruction by a variety of mechanisms

B cells & antibodies B cells – white blood cells that attack invaders in blood – mature in Bone marrow Patrolling B cells – make antibodies against invader immediately Memory B cells – remembers invader – can make antibodies quickly the next time protects you from getting disease more than once

B cells immune response invader (foreign antigen) Y Y Y Y B cells Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y “reserves ” memory B cells Y Y Y Y Y Y Y Y Y Y Y Y Y B cells release antibodies patrol blood forever recognition 10 to 17 days Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y

What if the attacker gets past the B cells in the blood & infects some of your cells? You need trained assassins to kill off these infected cells! T Attack of the Killer T cells!

T cells T cells mature in Thymus Helper T cells – sound the alarm for rest of immune system Cytoxic or Killer T cells – destroy infected body cells Memory T cells – remembers invader & reacts against it again quickly Where’s that?

Cell-Mediated Immunity An antigen-presenting cell (APC) first displays a foreign antigen and one of the body’s own self proteins to a helper T cell The helper T cell’s receptors recognize the self- nonself complexes on the APC - The interaction activates the helper T cells – The helper T cell can then activate cytotoxic T cells with the same receptors – Helper T cells also stimulate the humoral responses Cytotoxic T cells( or Killer T cells) bind to infected body cells and destroy them

Attack of the Killer T cells Killer T cells destroy infected body cells – T cell binds to invaded cell – secretes perforating protein punctures cell membrane of infected cell cell bursts Perforin punctures cell membrane cell membrane Killer T cell cell membrane invaded cell vesicle

Cytotoxic T cells (Killer T) may help prevent cancer – The surface molecules of cancer cells are altered by the disease

Immune response invader invaders in bloodinvaders infect cells B cellsT cells macrophages helper T cells patrolling B cells memory B cells memory T cells killer T cells Y Y Y Y YY Y Y antibodies Y Y Y skin invaders in body Y Y Y Y YY Y Y antibodies Y Y Y

The immune system depends on our molecular fingerprints – “Self” is signaled by major histocompatibility complex (MHC), a group of proteins unique to the individual that is present on the surface of cells Can cause rejection of transplanted organs

DISORDERS OF THE IMMUNE SYSTEM Autoimmune diseases – The system turns against the body’s own molecules – Examples: Rheumatic fever, Type I Diabetes, Multiple Sclerosis, Rheumatoid arthritis, Lupus Rheumatoid arthritis

DISORDERS OF THE IMMUNE SYSTEM Immunodeficiency diseases – Immune components are lacking, and infections recur Ex: Acquired immune deficiency syndrome (AIDS) SCIDS HIV on a lymphocyte

AIDS – HIV (Human Immunodeficiency Virus) the virus that causes AIDS – HIV is transmitted mainly in blood and semen – HIV kills helper T- cells and leads to AIDS

DISORDERS OF THE IMMUNE SYSTEM Allergies are overreactions to certain environmental antigens called allergens : Ex. Animal dander, dust mites, pollen release of histamine causes symptoms Antihistamines can relieve symptoms. anaphylactic shock: life threatening reaction to injected or ingested allergens.