Overview of the Immune System A historical perspective of immunology What is immunity Immunity is the state of protection against foreign pathogens or substances antigens Latin term immunis ID: 999236
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1. Kuby Immunology: Chapter 1Overview of the Immune System
2. A historical perspective of immunologyWhat is immunity?Immunity is the state of protection against foreign pathogens or substances (antigens)Latin term immunis, meaning “exempt,” is the source of the English word immunityObservations of immunity go back over 2000 yearsThucydides, an ancient historian, wrote in 430 bc of a plague in Athens where those who had recovered could safely nurse the currently ill
3. A historical perspective of immunologyCan we generate immunity without inducing disease? YES…through vaccinationVaccination prepares the immune system to eradicate an infectious agent before it causes diseaseWidespread vaccine use has saved many livesClassic examples: rabies vaccine and eradication of smallpox
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5. A historical perspective of immunologyA portion of immunity involves both humoral and cellular componentsHumoral immunity combats pathogens via antibodiesAntibodies are produced by B cellsAntibodies can be transferred between individuals to provide passive immunityCell-mediated immunity involves primarily T lymphocytesThese can eradicate pathogens, clear infected self-cells, or aid other cells in inducing immunity
6. A historical perspective of immunologyClonal selectionIndividual B and T cells each have an individual specificity for a single antigenThis is due to each cell having many copies of a receptor on their surface that only bind to one type of antigenWhen a B or T cell interacts with its specific antigen, it is selected and becomes activatedActivation results in a proliferation, producing a large number of clonesEach clone is reactive against the antigen that initially stimulated the original lymphocyte
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8. Important concepts for understanding the mammalian immune responsePathogens fall into four major categoriesImmune responses are quickly tailored to the type of organism involved
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10. Important concepts for understanding the mammalian immune responseImmune responses rely on recognition moleculesGerm-line encoded (pattern recognition receptors, PRRs)These bind to pathogen-associated molecular patterns (PAMPs)―generic molecules found on many different types of pathogens (e.g., peptidoglycan)Randomly generated (B and T cell receptors)These bind to very specific antigens, rather than generic molecules found on many pathogens
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12. Important concepts for understanding the mammalian immune responseHumoral and cell-mediated immunity relies on surface receptors (B and T cell receptors)These are randomly generated by DNA rearrangements in B and T cellsMany of these are nonviable and are deleted during development
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14. Important concepts for understanding the mammalian immune responseTolerance ensures that the immune system avoids destroying host tissueMany of the random rearrangements used to create B and T cell receptors could be anti-selfTolerance helps to keep these anti-self recognition molecules/cells from circulating in the bloodstream
15. Important concepts for understanding the mammalian immune responseIn response to pathogens, vertebrate immune systems use two interconnected systemsInnate immunityAdaptive immunity
16. Important concepts for understanding the mammalian immune responseInnate immune responsesFirst line of defenseFast, but nonspecificUses germ-line–encoded recognition moleculesAlso uses phagocytic cells
17. Important concepts for understanding the mammalian immune responseAdaptive immune responsesHumoral and cell-mediate responsesUsing B and T lymphocytes, respectivelySlower to develop5–6 days (or more)Use randomly generated antigen receptorsHighly specific to individual antigen molecules
18. Important concepts for understanding the mammalian immune responseInnate and adaptive immunity work cooperativelyActivation of innate immune responses produces signal molecules (often cytokines)These signal molecules stimulate and direct adaptive immune responses
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20. Important concepts for understanding the mammalian immune responseMemory is the hallmark of adaptive immunityPrimary response is initiated upon first exposure to an antigenMemory lymphocytes are left behind after antigen is clearedA second exposure to the same antigen re-stimulates memory lymphocytesReactivation yields faster, more significant, better responseMemory is NOT present in innate immunity
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22. The good, bad, and ugly of the immune systemDysfunctions of immunity―two broad categoriesOverly active or misdirected immune responsesAllergies/asthmaAutoimmune disease (e.g., multiple sclerosis, Crohn’s disease)ImmunodeficiencyPrimary (genetic) loss of immune functionSecondary (acquired) loss of immune functionOpportunistic infections (e.g., oral thrush) can occur in people with impaired immune responses
23. The good, bad, and ugly of the immune systemTransplanted tissuesA rare case where we want to AVOID an immune response (rejection)The body’s natural response to foreign tissue is to attack it and destroy itCancerA situation where the dangerous cells we want to target are our own self cellsGenerally tolerated and hard to generate immunity against
24. Active and Passive immunityThe form of immunity that is induced by exposure to a foreign antigen is called active immunity because the immunized individual plays an active role in responding to the antigen.Individuals and lymphocytes that have not encountered a particular antigen are said to be naïve.Individuals who have responded to a microbial antigen and are protected from subsequent exposures to that microbe are said to be immune.
25. Immunity can also be conferred on an individual by transferring serum or lymphocytes from a specifically immunized individual in experimental situations, a process known as adoptive transfer Therefore, this form of immunity is called passive immunity.The recipient of such a transfer becomes immune to the particular antigen without ever having been exposed to or having responded to that antigen.Passive immunization is a useful method for conferring resistance rapidly, without having to wait for an active immune response to develop.Active and Passive immunity
26. A physiologically important example of passive immunity is :Transfer of maternal antibodies through the placenta to the fetus, which enables newborns to combat infections before they develop the ability to produce antibodies themselves. Passive immunization against toxins by the administration of antibodies from immunized animals is a lifesaving treatment for potentially lethal infections, such as rabies, and snake bites.
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28. SummaryImmunity is a complex subject, broken down into many different layers and areasUnderstanding how immunity works allows us to:Exploit it to prevent infections (vaccination)Exploit it to treat illness (shutting down autoimmune disease or ramping up anti-cancer responses)Provide safer organ and tissue transplants