2 While some organisms can live symbiotically within animals, there are MANY that cause harm Humans have a three level defense system:
3 First Line of Defense Nonspecific defense Skin: Physical barrier covered with acidic secretions (pH 3-5)Mucus: Viscous fluid excreted by cells of mucous membranes traps microbes and other particlesCilia: Line the lungs and “sweep” invaders outGastric Juice: Kills most microbes in stomachAntimicrobial Proteins: Protective proteinsEx: Lysozyme digests cell walls of many bacteriaSymbiotic Bacteria: out compete other organisms that could cause harm (ex: some found in digestive tract)
4 Second Line of Defense Nonspecific defense Phagocytes WBCs (leukocytes)Use phagocytosis – process of “ingest and destroy”NeutrophilsMost common phagocyteShort life span60-70% of WBCsCells damaged by invading microbes release signals that attract neutrophilsNeutrophils enter the infected tissue, engulfing and destroying microbes there
5 MonocytesAnother type of phagocyteOnly 5% of WBCsMore effective than neutrophilsGrow into bigger phagocytic cells called macrophagesMacrophages: Effective, long-lived phagocytesNatural Killer Cells (NK Cells)Not phagocyticInstead they attack a cell’s membrane, causing it to lyse (burst open)Destroy virus-infected body cells and abnormal body cells
6 Antimicrobial Proteins “Complement” is a group of proteins that help defense reactionsHelp attract phagocytes to foreign cellsHelp destroy foreign cells by promoting lysisInterferonsSecreted by cells invaded by virusesStimulate neighboring cells to make proteins that will help them defend against the viruses
7 The Inflammatory Response Triggered by:Damage to tissue by a physical injuryEntry of microorganisms1) Injured tissue releases chemical signals like histamine which is secreted by basophilsBasophils: WBC’s found in connective tissue2) Histamine stimulates vasodilation in nearby capillaries, making them more permeable for clotting factors and other fluids. Clotting begins.
8 3) Factors released by various kinds of cells attract 3) Factors released by various kinds of cells attract phagocytic cells from the blood4) Phagocytic cells consume pathogens and cell debris. “Complement” proteins help the phagocytic cells, stimulate basophils to release histamine, and help lyse foreign cells. The tissue heals.
10 Third Line of Defense The Immune Response Different from the first two lines of defense in that it is SPECIFICAntigen: Any molecule that can be identified as foreignMHCMajor Histocompatibility ComplexGlycoproteins on the membranes of all body cellsMHCs are unique to the individual (except for iden. twins)Allows immune system to recognize difference between self and non-self cells
11 LymphocytesThe key cells of the immune systemGenerate efficient & selective immune responsesTwo main types: B cells & T cellsB cellsAlso called “B lymphocytes”Originate & mature in bone marrowRespond to antigensSurface of B cell membranes have antigen receptors called antibodies
12 Protein that is specific to a certain antigen AntibodiesProtein that is specific to a certain antigenAlso referred to as immunoglobulinsFive classes: IgA, IgD, IgE, IgG, IgMEach class has a different roleEach is a variant of a basic y-shaped proteinThe “variable” region of the antibody is what makes that particular antibody unique to a specific antigenAntibodies work by binding to antigens and inactivating themAfter inactivation:Macrophages use phagocytosisAntibodies stimulate “complement” proteins to lyse pathogens
14 Plasma Cells: Type of B Cell that secretes antibodies Memory Cells: So back to B Cells. When they have antigens bind to their antibodies, they produce two kinds of daughterB Cells:Plasma Cells: Type of B Cell that secretes antibodiesMemory Cells:Long-lived B Cells formed during the primary immune response.Circulate through the body, don’t release their antibodies yet.Ready to respond quickly to any future exposure to the same antigen.Activated memory cells mount the secondary immune response.Can result in immunity after a first exposure.
16 T CellsLymphocytes that come from bone marrowMature in the thymus glandMembranes have antigen receptorsNot antibodies, but recognition sites that are specific for molecules displayed by non-self cellsMHC markers on the membrane of cells distinguish between self & non-selfCancer cells & transplant cells are recognized as non-selfCells that have been infected by a virus show both self & non-self markers, but T Cells recognize this as non-self
17 When T Cells find non-self cells, they produce two kinds of cells: Cytotoxic T Cells (Killer T Cells): Bind to and lyse infected cells or cancer cells, killing themHelper T Cells: Stimulates production of B cells & cytotoxic T cells
18 Clonal Selection The antigen-driven cloning of lymphocytes When an antigen binds to a specific receptor it is selectively activating a small fraction of cells from the HUGE pool of lymphocytesThe small number of “selected” cells will grow into thousands that are specific for killing that antigen
20 Humoral Immune Response Responds to antigensB Cells make plasma cells & memory cellsPlasma cells release antibodiesMemory cells are for future useIf antigen does not stimulate production of B Cells:Macrophage takes in antigenT cells bind to macrophageHelper T cells give off interleukins that stimulate B cell production
21 Cell-mediated Immune Response Doesn’t involve antibodiesUses mostly T cellsResponds to non-self cellsT cells make cytotoxic T cells & helper T cellsHelper T cells bind to macrophagesThey bind to macrophages that have taken in antigens, because they present as “non-self”Helper T cells make interleukins which stimulate the growth of T cells & B cellsAnimation: The Immune Response
23 Other Immunity Vaccines Passive Immunity Stimulate production of memory cellsInactivated viruses/bacteria are used as vaccinesGives the immune system a “sneak preview” of an antigenNow if an individual is exposed in the future there will be a swift response before disease can set inPassive ImmunityGetting antibodies from someone who previously had a diseaseNewborns can have passive immunity from antibodies in mothers breast milk and antibodies that crossed placenta