The Body’s Defenses - Central Bucks School District



OLD NOTES – FOR REFERENCE ONLY!Chapter 43 – The Body’s DefensesThe Body’s DefensesNonspecific response that does not discriminate one infectious agent from anotherSpecific responds in specific ways to particular microorganisms3 lines of defense: First line external (epithelial tissue; ex. skin and mucous membranes) - NONSPECIFICSecond line internal (phagocytic cells and antimicrobial proteins indiscriminately attack invaders) - NONSPECIFIC5257800137160Note: White Blood Cells (wbc’s) are called leukocytes00Note: White Blood Cells (wbc’s) are called leukocytesThird line internal (immune system) – SPECIFICFig. 43.1 pg. 901Nonspecific Defenses Against InfectionExternal nonspecific defenseSkin and mucous membrane is first line of defense; inhibits microbes from entering bodySkin has a pH of 3 to 5, which is acidic enough to kill some microbesSecretions (saliva, tears, mucous) contain antimicrobial proteinsContains enzyme lysozyme (digests cell walls of bacteria)Mucus traps microbes Internal nonspecific defense depends on phagocytosis (ingestion of invading organisms by white blood cells); uses phagocytes, NK cells, inflammation, and antimicrobial proteinsNeutrophils60-70% of all wbc’sDamaged cells release signals that attract neutrophils; they then attack and engulf the invadersSelf-destruct; lifespan = few daysMonocytes5% of wbc’sCirculate in blood then migrate into tissue where they form macrophages (“big eaters”); very largeSome migrate throughout the body and some stay in certain tissues; phagocyticEosinophils1.5% of wbc’sDefend against larger parasites (ex. Blood flukes)Position against invader and secrete destructive enzymesNatural Killer (NK) cellsDestroy virus-infected body cells (don’t attack the microorganism directly)Inflammatory ResponseDamage to tissue causes a inflammatory responseIncreased blood supply to areaCharacteristic redness and heatInitiated by chemical signals (both from microorganism itself OR released from the body)Ex. Histamine released from circulating wbc’s (basophils)When the basophils are injured, they release histamine which triggers dilation and increased permeability of nearby capillariesBlood clotting marks beginning of repair process (blocks spread of microbes)Phagocytes migrate to area of infection within the hourchemokines – chemicals that attract phagocytes to area of injuryAnother sign of infection is feverFig. 43.5 pg. 903Antimicrobial ProteinsNonspecific can attack microbes directly or impede reproductionComplement System a group of at least 20 blood proteins that cooperate with other defense mechanisms; may amplify the inflammatory response, enhance phagocytosis, or directly lyse pathogens; activated by the onset of the immune response or by surface antigens on the microorganisms or other foreign cells Interferons limit cell-to-cell spread of virusesSecreted by virus-infected cellsDiffuses to neighboring cells and induces them to make other chemicals that hinder viral reproductionHow Specific Immunity ArisesLymphocytes = key of immune system; provide specificity and diversity; originate from pluripotent stem cells in the bone marrow or liver of a developing fetus; two main types: B lymphocytes (B cells) – cells remain in bone marrow and become B cellsT lymphocytes (T cells) – cells migrate from the bone marrow to the thymus (gland above the heart) and develop into T cellsLymphocytes are concentrated in the spleen, lymph nodes, and lymphatic tissue; circulate throughout the blood and lymphAntigen = foreign molecule that elicits a response from a lymphocyteOne way it gets a response activates B cells to secrete antibodies (specific!)B cells and T cells recognize specific antigens by their antigen receptors (PM bound)Lymphocytes (when activated by a microorganism binding to it) form 2 clones (it divides and differentiates):Effector cells combat antigen; short livedMemory cells long lived; stay around in case of a secondary “attack”Fig. 43.6 pg. 905So even if only a few lymphocytes are activated, thousands of cells result specific for that antigen (because of the cloning)Primary Immune Response: first time a body is exposed to an antigen10-17 days to get maximum response (effector B and T cells made)Secondary Immune Response: second time a person is exposed to an antigenResponse is faster; antibodies produced more quickly; these antibodies usually have a higher affinity for the antigen then the original ones did this is called Immunological MemoryImmune tolerance of selfDuring development, lymphocytes are tested for tolerance of “self” proteins; those that don’t recognize “self” become nonfunctional or are destroyed by apoptosisThis leads to self-tolerance so your own immune system doesn’t attack your own cellsMHC – Major Histocompatability complex mark body as “self”-3810048895Self = MHC moleculeNonself = antigen fragment00Self = MHC moleculeNonself = antigen fragmentMHC is a family of genes that encodes the glycoproteins in cell membranesClass I MHC molecules found on almost every cell of the bodyClass II MHC molecules restricted to few types of cells (macrophages, B cells, activated T cells)MHC molecules vary from person to person (helps with allowing some survivors for an epidemic – some may be immune to microorganism)In humans, the MHC is also known as the HLA (human leukocyte antigens)Two main types of T cells (each responds to either MHC I or MHC II):Cytotoxic T cells (Tc) – bind to MHC I molecules; kill infected cellsHelper T cells (TH) – bind to MHC II moleculesFig. 43.9 pg. 907Antigen-Presenting Cells (APC’s) cells that ingest bacteria and viruses and then destroy them; Class II MHC molecules in these cells collect peptide remnants of this degradation and present them to helper T cellsImmune ResponsesTwo major types of responses to antigensHumoral immunity B cells activated; defend against free bacteria, toxins, and viruses present in body fluidsCell-mediated immunity T cells used; active against viruses and bacteria within infected body cells APC (cells that engulf foreign antigens) alert the immune system (via T-cells) that a foreign antigen is in the bodyAPC’s “show” T-cells the foreign antigensThe helper T-cells have a surface protein called CD4 that binds to part of the class II MHC protein-1905026035Class II MHC recognized by TH (helper T cells)Class I MHC recognized by TC (cytotoxic T cells)00Class II MHC recognized by TH (helper T cells)Class I MHC recognized by TC (cytotoxic T cells)Cytokines molecules secreted by activated TH cells that stimulate other lymphocytesFig. 43.10 pg. 909Cytotoxic T-cells (TC) attack intracellular pathogens and cancer cellsSurface protein (CD8) = recognition4781550240030Cell Mediated Immunity attack on infected cellsHumoral Immunity secretion of antibodies by plasma cells; extracellular pathogens00Cell Mediated Immunity attack on infected cellsHumoral Immunity secretion of antibodies by plasma cells; extracellular pathogenskills infected cells by releasing perforin (forms holes in target cells membrane; cell eventually lyses)Fig. 43.11 pg. 910Fig. 43.12 pg. 910Humoral ResponseB-cells make antibodies against extracellular pathogensFig. 43.13 pg. 911B-cell activation is initiated by cytokines secreted from TH cells that are activated by the same antigenB-cells activate into: Antibody secreting plasma cellsMemory B-cellsT-dependent responses: Need the help of TH cells to stimulate antibody productionMOST proteins are T-dependentT-independent responses: Don’t need TH cells; the response is weaker than T-dependent responses; creates NO memory cellsB-cells (class II MHC molecules) are antigen-presenting cellsB cell binds to antigen and takes in a few of the foreign molecules (endocytosis)B cell then presents the antigen to the TH cellAntibody Structure/FunctionEpitope accessible part of the antigen that the antibody interacts with; one antigen may have several epitopesAntibodies make up the group immunoglobulins (proteins)Antibodies usually have 2 identical antigen-binding sites specific for the epitope that provoked its productionStructureTwo identical heavy chains and two identical light chains linked together by disulfide bridges in a Y-shapeAt the tips of the Y, there are variable regions (V) because they vary from antibody to antibody. The rest of the antibody is made up of constant regions (C) because they vary little from antibody to antibodyFive different classes of antibodies; based on differences in the C regions of the heavy chainsAntibody mediated disposal of antigenAntibody binds to the antigen to form the antigen-antibody complex Neutralization binding blocks the activity of the antigenOpsonization bound antibodies enhance attachment of macrophages (yields phagocytosis)Agglutination clumping of bacteria or viruses; occurs b/c each antibody has at least two antigen binding sites; these large complexes are phagocytosed by macrophagesComplement Fixation activation of the complement system (serum proteins are activated); yields lysis of many types of viruses and pathogenic cellsInverts Immune SystemDistinguishing self from non-self is seen in animals as simple as spongesDispose of what is non-self by phagocytosisRely on non-specific mechanisms of defense (not antigen-specific mechanisms)However, SOME produce some antibodiesDo not show immunological memoryImmunity in Health and DiseaseActive Immunity depends on response of persons own immune system (ex. Getting over chicken pox)Can be acquired naturally or by immunization/vaccinationPassive Immunity antibodies are transferred from one person to another (ex. Antibodies of a pregnant woman cross the placenta into the fetus; breast milk)Lasts only as long as those antibodies last (weeks to months)The immune systems ability to distinguish self from non-self limits blood transfusion and tissue transplantationPlacenta plays an important role in fetus development because a woman’s body does not reject the fetus as a foreign substanceBlood TypingA blood makes antibodies to B-like epitopesB blood makes antibodies to A-like epitopesO blood makes antibodies to both A and B-like epitopesNo memory cells with blood cells, so each occurrence is like a primary responseRh factor (problem if mom is Rh neg and fetus is Rh pos if small amounts of blood cross the placenta)Tissue Grafts and Organ TransplantationMHC, which encodes the protein fingerprint unique to each individual, is responsible for stimulating the rejection of tissue grafts and organ transplantsAttempts made to match MHC between donor and recipient as closely as possibleCan give medicine to suppress the immune response, but that makes the recipient more susceptible to infectionAllergies are exaggerated responses to certain environmental antigensHistamines are released when these antigens bind; histamine causes dilation and increased permeability of the small blood vessels; this causes allergy symptoms (runny nose, watery eyes, etc.)Antihistamines decrease allergy symptoms by blocking receptors for histamineAnaphylactic shock life-threatening reaction to injected or ingested allergens (ex. bee stings, penicillin, peanuts, fish); triggers abrupt dilation of peripheral blood vessels causing a quick drop in blood pressure; death may occur in a few minutesAutoimmune DiseasesLoses tolerance of self and turns against your own cells (ex. lupus, arthritis, MS)Caused by some failure in immune regulationImmunodeficiency DiseasesEither the humoral or the cell-mediated immune systems fail (sometimes both!)Working on gene therapy’s to fixCancers (ex. Hodgkin’s disease), AIDS function as immunodeficiency diseasesAIDSImmunodeficiency disease caused by a virusSusceptible to opportunistic diseases (those that take advantage of weakened immune system)Caused by HIV; most lethal pathogen ever encounteredEvolution of drug-resistant strains of HIV is a problem, so they use a combination of drugs ................
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