Immune System Overview
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Transcript of Immune System Overview
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Immune System Overview
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Why an immune system?We are outnumbered! Viruses and bacteria
are everywhere!Humans offer limitless resources for
pathogens EnergyReproductive potential
Getting into the body isn’t easy!
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Meet the enemyBacteria
Free-livingNot all are bad!Pathogenic ones produce toxins that damage
human tissueViruses
Obligate parasitesHijack human cells; convert to virus-producers,
killing host cell in the process(And fungi, protozoa too…)
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A human fortressSkin is thick – hard to penetrateProduces substances that deter invasion:
Skin pH (not favorable)Mucus (sticky trap)Lysozymes (digest bacteria)
Specialized traps around vulnerable areas (Eyes, noes, mouth)Cilia sweep away invaders that are trappedStomach acid kills ingested invaders
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…but we do get sick!Enter through weak points:
FoodNoseBreak in skin/scrapes
Cells are damaged/destroyed Dying cells release distress chemicals
(histamine) Triggers inflammation (blood vessel dilation,
increased blood flow) Draws defensive cells to area (generalized white
blood cells)
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How do we tell “friend” from “foe”?All cells present antigens – surface
molecules that identify identity(antigen = antibody generator)
Immune system reacts to foreign antigens
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A complex system!Several “lines” of defense:1. Barriers (First line of defense)2. Generalized defenders (Second line of
defense)3. Specific defenders AND memory (Third line of
defense)
Consist of:Several types of cellsProteins
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The Complement SystemPart of second line of defenseFree-flowing proteins found in bloodQuickly reach site of invasionReact to antigensWhen activated, can
Trigger inflammationAttract “eater cells” (macrophages)Coat pathogen (make macrophages’ job easier)Kill intruder directly
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PhagocytesFind and “eat” bacteria, viruses, dead/injured
body cells by phagocytosis3 types:
Granulocytes (some)MacrophagesDendritic cells
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GranulocytesOften first to site of infectionNumerousShort lifespan“Pus” in infected wounds chiefly composed of
granulocytes
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Macrophage“Big eaters”Slower to respond to invader than
granulocyteLarger, longer-lived, more capable
Help alert rest of immune system to invaderStart as monocytes; become macrophages
when entering bloodstream
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Dendritic cells“Eater” cells Help with immune system activation – act as
antigen-presenting cellsFilter bodily fluids to clear foreign organisms
and particles
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3rd Line of Defense: Humoral/Fluids Cell-MediatedFocus: catch invader
before infection of cellsIncludes Antibodies to
deactivate/eliminate threat in bodily fluids
Deals with infection that has already entered cells
Focus: destruction of infected cells so it doesn’t spread!
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Lymphocytes – Part of both humoral and cell-mediatedT and B cellsOriginate in bone marrowMigrate to lymph nodes, spleen, thymus to
matureLymph vessels
transport, store lymphocytesFeeds cells into bodyFilter out dead cells/invading organisms
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ReceptorsEach lymphatic cell contains surface
receptors Recognize foreign antigens as cells pass by…Specialized for a particular antigen
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T cells – Cell-mediated immunityPrimary focus = infected cellsTwo types: helper and killerT = thymus (site of maturation)
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Helper T cellMain regulator of third line of defensePrimary task: activate other cells (B and
killer T cells)Usually activated by macrophages/dendritic
cells (during antigen presentation)
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Killer T cellDirectly attacks body cells infected by
pathogen, cancer cellsReceptors used to determine if each cell
encountered is self/non-self (compare to accepted receptors, MHC)
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B lymphocyte cell – Humoral immunitySearches for intact antigens matching
receptorIf a match is found…
Connects to antigenTriggering signal set off…
T helper proteins help fully activate B cellProduces 1000’s of clones: differentiate into
plasma cells or B memory cells
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Plasma CellProduces antibodiesResponds to same antigen matched by B cell
receptorSeek out intruders, help destroy themRelease tens of thousands/second
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AntibodiesY-shapedAttach to matching antigens
Enhance phagocytosis of macrophages (label for capture)
Neutralize toxinsIncapacitate viruses (coat surface proteins)Group pathogens by linking (agglutination)
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5 types of antibodies (Ig’s):IgG Most common; fight bacterial infections; pass from mom to
child in placenta (G = mom’s gift)
IgA In mucous membranes of digestive system, milk, tears, saliva (A = a lot of mucus)
IgM Natural defenses against general bacterial infections (M=most bacteria)
IgE Stimulate basophils and mast cells to defend against parasites fungi and worms (E=eeeww!)
IgD On membranes of B-lymphocytes; form plasma and memory cells (D=defend blood)
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Memory cellsProlonged lifespan“Remember” specific intrudersBoth B and T cells have memory cellsHelps trigger immune system to respond
more quickly if invader reappears
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InflammationOutcome of secondary immune responseIncreases blood flow to affected area
Blood vessels dilate to increase blood flowImmune cells go to affected areaImmune response takes place at the site it’s neededTissues = red and swollen because of the blood that
enters the area; increasing temperature = antimicrobial
Pain from pressure of swollen tissues on nerve endingsNormal functions return when the tissue is fully
recovered
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Immunization and VaccinationNatural Immunity
Natural: exposed to foreign antigens as part of everyday life Acquired immunity – body responds to foreign
antigens and develops immunity using B and T lymphocytes
Passive immunity Embryological development when antibodies
(Ig’s) from the mother’s blood stream are passed to the fetus
Post-natal – baby receives antibodies via milk
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Artificial ImmunityActive: Vaccinations
Therapeutic exposure to antigensStimulates the secondary response by
introducing pathogenic material (inactivated, attenuated, or partial) into the body
Vaccines are typically used for viruses! Antibiotics are only for bacteria
Passive: Antibody transferPatient receives (via injection) large amounts
of antibodies to fight disease Globulin injections can remove certain
microorganisms from the body