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Transcript
Immunology The Body’s Defenses Chapter 33 I. How Microbes Cause Disease A. pathogen • B. antigens (ag) • C. D. any substance that triggers the immune system to respond infections can be superficial or systemic, or one then the other bacteria 1. 2. 3. 4. 5. E. adherence (with adhesions or fimbriae) colonization invasiveness toxins: damage to cells/tissues damage to host enzymes: increase virulence, degrade cells/tissues, cause/dissolve clots capsule: helps resist phagocytosis viruses • F. replication inside host cells (lytic and lysogenic cycles) fungi 1. 2. 3. G. usually cause superficial infections through enzymes (e.g., keratinase) allergic reactions toxins protists (protozoa) 1. 2. H. ingest host cells and fluids invade rbc’s algae • I. any disease-causing organism neurotoxins disease transmission can be direct or indirect II. Host Defense A. nonspecific defenses 1. very general (broad spectrum) work on any antigen 2. not as strong as specific defenses 3. first line a. anatomical barriers i. intact skin and secretions of skin ii. saliva and mucous b. coughing and sneezing reflexes c. normal flora i. bacteria normally living in body compete with pathogens ii. slow down growth of pathogen or spread of antigen 4. second line a. phagocytic leukocytes (wbc's) i. neutrophils: release some destructive chemicals ii. eosinophils: defense against larger parasites iii. monocytes: immature macrophages iv. macrophages: act as antigen-presenting cells (APC's) v. dendritic cells: act as antigen-presenting cells (APC's) Fig. 33.5 A macrophage engulfing multiple bacteria b. other nonspecific leukocytes (not phagocytic) i. basophils: release histamine and heparin ii. natural killer (NK) cells: destroy viral-infected and tumor cells c. antimicrobial substances i. ii. tears (lysozyme) transferrins • • iron-binding proteins in blood reduce available Fe for pathogen d. molecular defenses i. interferon • ii. by some antitoxins • iii. neutralize toxins complement system • • e. anti-viral protein produced infected cells 20+ proteins in blood many functions inflammation and fever i. ii. confine infection raise temp. above pathogen’s normal range Fig. 33.6 Action of the complement system against bacteria Fig. 33.3 A summary of nonspecific defenses B. specific defenses (third line of defense) 1. 2. 3. respond only to one antigen at a time (narrow spectrum) stronger than nonspecific defenses specific leukocytes (lymphocytes) a. b. 4. T-cells B-cells plasma cells antibodies (immunoglobulins; ab) • proteins that bind specifically (lock-and-key) to antigens (ag) 5. some antitoxins III. Specific Immunity A. kinds of immunity innate: genetics or 1st and 2nd line only acquired: some way other than genetics; involves specific defenses 1. 2. a. active: body makes it’s own ab’s i. naturally acquired active: by having a disease ii. artificially acquired active: through vaccine • weakened or dead form of antigen causes immune response b. B. passive: body obtains ab’s through external source i. naturally acquired passive: across placenta or in breast milk ii. artificially acquired passive: through immune serum antigens (ag) 1. usually parts of pathogens • foreign proteins or carbs of certain size C. cells and tissues involved in specific immunity 1. specific leukocytes (lymphocytes) B-cells produce ab i. become plasma cells secrete ab ii. memory cells protect if invaded by same pathogen again b. T-cells i. cytotoxic (Tc) • destroy viral-infected, tumor, or foreign cells ii. helper (Th) • activate Tc, B-cells, and other immune cells iii. suppressor (Ts) • turn immune system off after infection iv. memory (Tm) • become Tc or Th to protect against same antigen a. 2. circulatory and lymphatic systems a. b. c. transport immune substances to site of infection leukocytes concentrate and mature in lymph nodes immune surveillance • lymph nodes, Tc, macrophages, NK cells D. four general properties • recognition, specificity, heterogeneity, memory Fig. 33.14 Action of cytotoxic T-cells Cytotoxic T-cells attacking and destroying a cancer cell (target cell) IV. Dual Nature of Immune System A. humoral immunity (antibody-mediated) 1. a. b. 2. 3. a. b. 4. a. b. c. d. e. consists of: B-cells, plasma cells, memory cells Ab circulating in blood defends against extracellular pathogens and free ag properties and structure of Ab’s heavy vs. light chains constant vs. variable regions classes of Ab’s IgG IgM IgA IgE IgD Fig. 33.11 Structure of an antibody The five classes of antibodies 5. ab’s work by neutralizing an ag a. neutralization renders ag ineffective b. ways of accomplishing this: i. coat ag to prevent adherence ii. enhance phagocytosis • coat surface of ag o opsonization • clump many ag’s together o agglutination • precipitate soluble antigen iii. act as antitoxins iv. trigger inflammation and fever v. activate complement system The action and work of antibodies 6. T-cell influence • Th cells bring ag to B-cells activate B-cells ab produced B. cell-mediated immunity 1. consists of: a. direct action of T-cells (esp., Th and Tc) b. nonspecific leukocytes • phagocytic wbc’s, basophils, NK cells 2. defends against intracellular pathogens and cancer 3. process: a. some macrophages act as antigen-presenting cells (APC's) • bring ag to Th cells Th cells activated b. Th cells bring ag to B-cells and Tc cells B-cells and Tc cells activated c. major histocompatibility complex (MHC) • protein on all of an individual’s cells that identifies “self” tissue C. immune cells communicate with each other through various chemicals Fig. 33.7 A summary of specific defenses V. Sequence of Events Occurring During a Typical, First-Time Infection • pathogen (ag) invades and damages body nonspecific defense activate (2nd line) macrophage phagocytizes a pathogen macrophage displays ag on its surface macrophage presents (APC) ag to a Th cell Th cell brings ag to B-cells and activates other T-cells (esp., Tc cells) Bcells produce ab in response to ag some B-cells become plasma cells plasma cells release ab ab’s and various T-cells begin attacking ag some B-cells and T-cells (Th, Tc) become memory cells near end of infection Ts cells turn immune system off An overview of the immune response VI. Immunologic Memory A. B. immune system remembers what it has been exposed to previously 1. responds very quickly and efficiently to such ag’s a. memory B-cells become plasma cells release large amts. of ab b. memory T-cells (Tm) become Th and Tc cells quickly attack ag 2. most often, symptoms do not even occur primary vs. secondary response VII. Factors That May Modify the Immune Response A. B. C. D. E. F. G. compromised host genetics age nutrition effect of injury environment stress Fig. 33.9 Primary and secondary response