2Immune System Overview Function: fight infection through the production of [specialized] cells that inactivate foreign substances or cellsIt is main defense against pathogensRecognizes, attacks, destroys, and “remembers” each type of pathogen that enters the body2 general categories:Nonspecific defenses (fortress walls of the body)Specific defenses (security guards of the body)
3Nonspecific Defenses First line of defense: skin Most important nonspecific defense!Very few pathogens can penetrate the skinMust have an opening – a cut, scratch, mouth, noseMucus, saliva, and tears have lysozyme – enzyme that breaks down bacteria’s cell wallOil and sweat glands produce acidic environmentMucus and cilia in nose and throat trap and push pathogens away from lungsAcid and enzymes destroy bacteria that make it to your stomach
4Nonspecific Defenses Second line of defense: inflammatory response Reaction to tissue damage caused by injury/infectionWhen pathogens are detected:White blood cells flood area through blood vessels near woundMany WBC are phagocytes – engulf and destroyReleases chemicals that increase core body temperature (fever)Many pathogens only survive in narrow temp. rangeIncreased temp also increases heart rate = more WBC
6Nonspecific Defense to Viruses Sometimes, virus-infected cells produce a group of proteins that help other cells resist infection: InterferonsNamed this because they “interfere” with growth of the virusSlows the progress of infection and gives specific defense system time to respond
7Specific Defenses Called “immune response” Triggered by antigens 2 types of lymphocytesB lymphocytes (B cells) – work in body fluidsHumoral immunityT lymphocytes (T cells) – work in living cellsCell-mediated immunity
8Humoral Immunity B cells detect pathogen and multiply rapidly Produces large numbers of plasma cells and memory B cellsPlasma cells release antibodies (proteins that recognize and bind to antigens – recall blood types!)Antibodies carried in the blood stream to attackMemory B cells remain capable of producing antibodies specific to that pathogen after exposure
10Antibody StructureAntibody is shaped like a “Y” and has two identical antigen binding sitesDifferences in amino acids affect shape of binding sitesShape of binding site is how antibody recognizes antigenHealthy adult can produce about 100 million different types of antibodies!
11Cell-Mediated Immunity Primary defense against own cells when cancerous or infectedAlso important for fighting fungi and protistsProcess: T cells divide and differentiate into…Killer T cells – destroy bacteria, fungi, protozoan or foreign tissue with the antigenHelper T cells – produce memory T cellsSuppressor T cells – shut down killer T cells after pathogenic cells brought under controlMemory T cells – cause response if same antigen enters again
12Yellow objects are killer T cells attaching cancer cell (SEM)
13Transplants Killer T cells make organ transplants difficult Recognize new organ as foreign and attack itCalled “rejection”To prevent rejection, donor should have cell markers nearly identical to recipient; andRecipient usually takes drugs for the rest of their life to suppress cell-mediated immune response.
14Acquired Immunity Remember Jenner’s smallpox?? Cowpox infection to create immunity to smallpoxCan be active or passive
15Active vs. Passive Immunity Type of immunity produced by reaction to a vaccineVaccination: injection of weakened or mild form of pathogenStimulate immune system to create plasma cellsPlasma cells are ready to make specific antibodiesAppears AFTER exposureCan be natural or deliberateAntibodies produced by other animals injected into the bloodstreamLasts for short time – body eventually destroys themCan be natural or deliberateNatural: from mother to fetus or in breastmilkDeliberate: vaccineTropical diseasesRabies