Chapter 43. Immune System phagocytic leukocyte lymphocytes attacking cancer cell lymph system 2008-2009

Why an immune system? Attack from outside Attack from inside animals must defend themselves against unwelcome invaders viruses  protists bacteria  fungi we are a tasty vitamin-packed meal cells are packages of macromolecules no cell wall traded mobility for susceptibility Attack from inside defend against abnormal body cells = cancers 2008-2009

Lines of defense 1st line: Barriers 2nd line: Non-specific patrol broad, innate, external defense “barbed wire” skin & mucus membranes 2nd line: Non-specific patrol broad, innate, internal defense “untrained soldiers” leukocytes (WBCs) 3rd line: Immune system specific, acquired immunity “elite trained units” lymphocytes & antibodies 2008-2009

1st: External defense non-specific defense external barrier epithelial cells & mucus membranes skin respiratory system digestive system genito-urinary tract Lining of trachea: ciliated cells & mucus secreting cells 2008-2009

1st: Chemical barriers on epithelium Skin & mucous membrane secretions sweat pH 3-5 tears washing action mucus traps microbes saliva anti-baterial = “lick your wounds” stomach acid pH 2-3 anti-microbial proteins lysozyme digests bacterial cell walls 2008-2009

2nd: Internal, broad range patrol innate defense rapid response cells & proteins attack invaders that penetrate body’s outer barriers leukocytes phagocytic white blood cells anti-microbial proteins inflammatory response natural killer cells leukocytes 2008-2009

Leukocytes: Phagocytic WBCs Neutrophils attracted by chemical signals released by damaged cells (interferon) enter infected tissue, engulf & ingest microbes amoeba-like lysosomes ~3 day life span Macrophages “big eater” bigger, long-lived phagocytes 2008-2009

Phagocytes macrophage yeast 2008-2009

Lymph system Production & transport of leukocytes Traps foreign invaders Lymph system lymph vessels (intertwined amongst blood vessels) 2008-2009 lymph node

Development of Red & White blood cells Red blood cells inflammatory response fight parasites develop into macrophages short-lived phagocytes 60-70% WBC 2008-2009

Inflammatory response Reaction to tissue damage Pin or splinter Blood clot swelling Bacteria Chemical alarm signals Phagocytes 2008-2009 Blood vessel

Inflammatory response Damage to tissue triggers local inflammatory response histamines & prostaglandins released capillaries dilate, more permeable lead to clot formation increased blood supply swelling, redness & heat of inflammation & infection delivers WBC, RBC, platelets, clotting factors 2008-2009

Fever When a local response is not enough systemic response to infection activated macrophages release interleukin-1 triggers hypothalamus in brain to readjust body thermostat to raise body temperature higher temperature helps defense inhibits bacterial growth stimulates phagocytosis speeds up repair of tissues causes liver & spleen to store iron reducing blood iron levels bacteria need large amounts of iron to grow Certain bacterial infections can induce an overwhelming systemic inflammatory response leading to a condition known as septic shock. Characterized by high fever and low blood pressure, septic shock is the most common cause of death in U.S. critical care units. Clearly, while local inflammation is an essential step toward healing, widespread inflammation can be devastating. 2008-2009

3rd: Acquired Immunity Specific defense Responds to… lymphocytes B lymphocytes (B cells) T lymphocytes (T cells) antibodies immunoglobulins Responds to… specific microorganisms specific toxins abnormal body cells antigens 2008-2009

Antigens Proteins that serve as cellular name tags foreign antigens cause response from WBCs proteins belonging: viruses, bacteria, protozoa, parasitic worms, fungi, toxins non-pathogens: pollen & transplanted tissue B cells & T cells respond to different antigens B cells recognize intact antigens invaders in blood & lymph T cells recognize antigen fragments invaders which have infected cells “self” “foreign” 2008-2009

Lymphocytes B cells T cells mature in bone marrow humoral response system “humors” = body fluids produce antibodies T cells mature in thymus cellular response system Learn to distinguish “self” from “non-self” antigens during maturation Tens of millions of different T cells are produced, each one specializing in the recognition of oen particar antigen. 2008-2009

B cells Humoral response = “in fluid” Specific response defense against attackers circulating freely in blood & lymph Specific response recognizes specific antigen produces antibodies against it tagging protein = immunogloblin millions of different B cells, each produces different antibodies, each recognizes a different antigen types of B cells plasma cells immediate production of antibodies short term release memory cells long term immunity 2008-2009

each B cell has ~100,000 antigen receptors Y Y Y Y Y Antibodies Y Y Y Proteins that bind to a specific antigen multi-chain proteins produced by B cells antibodies match molecular shape of antigens immune system has antibodies to respond to millions of antigens (invaders) tagging system “this is foreign!” Y Y Y Y Y Y Y variable binding region Y Y Y Y each B cell has ~100,000 antigen receptors 2008-2009

How antibodies work 2008-2009

invader (foreign antigen) 10 to 17 days for full response B cell immune response B cells + antibodies Y tested by B cells invader (foreign antigen) memory cells “reserves” Y Y recognition Y captured invaders Y clone 1000s of clone cells plasma cells release antibodies Y Y 2008-2009

1° vs 2° response to disease Memory B cells allow a rapid, amplified response with future exposure to pathogen 2008-2009

How can we have so many antibody proteins & so few genes? Variable region Antibody Constant region Light chain B cell Heavy chain Variable DNA combinations: • 1M different B cells • 10M different T cells Translation of mRNA Rearrangement of DNA Transcription of gene V mRNA 40 genes for Variable region DNA of differentiated B cell D J C C Chromosome of undifferentiated B cell 2008-2009

Vaccinations Active immunity immune system exposed to harmless version of pathogen Stimulates immune system to produce antibodies to invader rapid response if future exposure Most successful against viral diseases 2008-2009

Jonas Salk 1914 – 1995 Developed first vaccine against polio Poliomyelitis (polio) is caused by a virus that enters the body through the mouth. The virus multiplies in the intestine and invades the nervous system. It can cause total paralysis in a matter of hours. One in 200 infections leads to irreversible paralysis. Among those paralyzed, 5-10 percent die when their breathing muscles are immobilized. Polio mainly affects children under age 5. April 12, 1955 2008-2009

Polio epidemics 1916 The first major polio epidemic strikes in the United States; 27,000 people suffer paralysis and 6,000 die. Increasing numbers of outbreaks occur each year. 1921 Franklin D. Roosevelt is diagnosed with polio. 1928 Iron lungs are introduced to help patients with acute polio breathe. 1932 Franklin D. Roosevelt is elected President of the United States 1949 Dr. John Enders, Dr. Frederick Robbins and Dr. Thomas Weller develop a way to grow poliovirus in tissue culture, a breakthrough that aided in the creation of the polio vaccine. Their work earned the three scientists the Nobel Prize in physiology and medicine in 1954. 1952 The United States reports 57,628 polio cases -- the worst U.S. epidemic on record. 1979 The last U.S. case of polio caused by wild poliovirus is reported. 1988 Worldwide, polio continues to affect some 350,000 people in 125 countries. 1994 The Americas are certified polio-free. 2000 The Western Pacific region is certified polio-free. 2002 Europe is certified polio-free. 2008-2009

Passive immunity Maternal immunity Injection antibodies pass from mother to baby across placenta or in breast milk critical role of breastfeeding in infant health mother is creating antibodies against pathogens baby is being exposed to Injection injection of antibodies short-term immunity 2008-2009

T cells Immune response to infected cells Kinds of T cells defense against invaders inside infected cells viruses & bacteria within infected cells, fungi, protozoa & parasitic worms defense against “non-self” cells cancer & transplant cells Kinds of T cells helper T cells stimulate immune system killer T cells attack infected body cells 2008-2009

How are cells tagged with antigens Glycoproteins on surface of cells have unique “fingerprint” major histocompatibility proteins (MHC) human leukocyte antigens (HLA) MHC proteins constantly export bits of cellular protein to cell surface “snapshot” of what is going on inside cell T cell MHC proteins displaying self-antigens 2008-2009

How do T cells know a cell is infected Infected cells digest some pathogens & export pieces to MHC proteins on cell surface antigen presenting cells (APC) invading pathogen MHC proteins displaying foreign antigens T cell T cell antigen receptors 2008-2009

activate killer T cells stimulate B cells & antibodies T cell response killer T cell activate killer T cells infected cell helper T cell interleukin 2 helper T cell interleukin 1 or stimulate B cells & antibodies Y activated macrophage interleukin 2 helper T cell Y 2008-2009

Attack of the Killer T cells Destroys infected body cells binds to target cell secretes perforin protein punctures cell membrane of infected cell Vesicle Killer T cell Killer T cell binds to infected cell Perforin punctures cell membrane Cell membrane Cell membrane 2008-2009 Infected cell destroyed Target cell

pathogen invasion antigen exposure antigens on infected cells Immune response pathogen invasion antigen exposure free antigens in blood antigens on infected cells macrophages humoral response cellular response B cells helper T cells T cells plasma B cells memory B cells memory T cells cytotoxic T cells Y antibodies 2008-2009

HIV & AIDS Human Immunodeficiency Virus virus infects helper T cells helper T cells don’t activate rest of immune system: T cells & B cells also destroy T cells Acquired ImmunoDeficiency Syndrome infections by opportunistic diseases death usually from other infections pneumonia or cancer 2008-2009

Immune system malfunctions Auto-immune diseases immune system attacks own molecules & cells lupus antibodies against many molecules released by normal breakdown of cells rheumatoid arthritis antibodies causing damage to cartilage & bone diabetes beta-islet cells of pancreas attacked & destroyed multiple sclerosis T cells attack myelin sheath of brain & spinal cord nerves Allergies over-reaction to environmental antigens allergens = proteins on pollen, from dust mites, in animal saliva 2008-2009

Key attributes of immune system 4 attributes that characterize the immune system as a whole specificity antigen-antibody specificity diversity react to millions of antigens memory rapid 2° response ability to distinguish self vs. non-self maturation & training process to reduce auto-immune disease 2008-2009