E2.Defense - Body Defenses Pathogens • Pathogen: an agent...

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Unformatted text preview: Body Defenses Pathogens • Pathogen: an agent causing a disease Body Defenses Pathogens & Immunity • Microbe: microscopic organism (most are not pathogens) – Bacteria – Protists (eukaryotic, single-celled) – Multicellular (fungi, parasites) • Infectious particles (non-living) – Viruses: nucleic acids wrapped in protein capsid – Prions: rogue proteins Pathogens First line of Defense: Barriers • Stratified squamous epithelia – Skin; mucous membranes • Flushing action – Urine, tears, saliva, sweat, oil glands • Mucus traps – Respiratory, digestive, and vaginal tracts • Lysozyme (enzyme digests bacterial walls) – Tears, sweat, saliva • Acidic pH – Stomach, vaginal secretions • High body temperature • Competition from microflora (resident microbes) Second line of Defense: Non-specific Responses Inflammatory Response • Macrophages and Fixed Phagocytes – Phagocytosis of any “non-self” cell • Inflammation • Hallmark symptoms of inflammation: redness, heat, swelling and pain Heyer 1 Body Defenses Third line of Defense: Specific Responses (Immunity) The Lymphatic System • B-lymphocytes & antibody-mediated defense The Lymphatic System • Lymphatic circulation • Lymphoid tissues – Esp . vs . bacteria, chemical toxins, & free viruses • T-lymphocytes & cell-mediated defense – Esp . vs . eukaryotic pathogens: parasites, viral-infected cells, cancerous cells, & transplanted tissues The Lymphatic System The Lymphatic System • Lymphatic circulation • Lymphoid tissues Lymphatic vessel with valve B-Lymphocytes (B-cells) The Lymphatic System • Lymph node Heyer • • • • • Type of white blood cell produced from stem cells in Bone marrow Secrete antibodies (binding proteins) Each primary B-cell produces only one specific antibody Each antibody binds one specific substance (antigen) Clonal Selection : If B-cell encounters its antigen, it replicates quickly to produce a large population (clone) of B-cells making that antibody 2 Body Defenses Antibody-mediated immunity by B-cells B-cell clone • Most as plasma cells — secrete lots of specific antibody to bind up specific antigen – Once antigen is gone, plasma cells self-destruct • Some as memory cells — remain in body until antigen is again encountered – Then replicate to make more plasma & memory cells – The more often a specific antigen is encountered, the more memory cells. Thus faster, bigger response in future T-Lymphocytes (T-cells) • • • Type of white blood cell produced from stem cells in bone marrow, but migrate and finish differentiation in Thymus Produce specific binding protein that remains anchored to T-cell surface (receptor) Clonal Selection : If T-cell encounters its antigen, it replicates quickly to produce a large population (clone) of T-cells making that receptor Antibody-mediated immunity by B-cells Antibody: Y-shaped protein with twin binding sites • Bind to toxin molecule or infectious particle – Prevent it from reacting or entering cells • Bind to molecule on surface of pathogen organism – Clump them together – “Tag ” them for endocytosis – Initiate “complement fixation” • Plasma proteins insert into its cell membrane causing lysis Cell-mediated immunity by T-cells T-cell clone • Most as helper T-cells — secrete cytokines that attract/activate specific & nonspecific defense cells – Some cytokines are interferons: block viral replication in infected cells • Many as cytotoxic T-cells — punch holes and cause selfdestruct of pathogen or infected cell • Some as memory cells — remain in body until antigen is again encountered Cell-mediated immunity by T-cells Immunization: Passive Immunity Passive: inoculate with antibodies Cytotoxic T-cells • Activated by helper T-cell cytokines • T-cell receptor (TCR) binds to antigen on target cell • Vesicles containing perforins and granzymes exocytosed onto target cell • Perforins form pores in target cell membrane • Granzymes initiate self-destruct Heyer – Maternal antibodies via placenta or breast-feeding – Anti-venom – General gamma-globulin shot (plasma protein fraction containing antibodies) – Monoclonal antibodies • Quick defense, but short duration immunity – Once antibodies are gone, so is immunity 3 Body Defenses Immunization: Active Immunity Active: stimulate body to make antibodies and/or T-cells • Exposure or inoculation with – Pathogen – Weakened or killed pathogen – Purified antigen from pathogen • Slower initial response, but longlasting immunity – Booster shots increase specific memory cell population – Faster & stronger response to subsequent exposures Immune System Disorders • Autoimmune diseases – Antibodies and/or cytotoxic TCRs bind to host molecules as if foreign Æ healthy tissues self-destruct • Type I diabetes, multiple sclerosis, lupus, myasthenia gravis, rheumatoid arthritis – Very difficult to treat: if damaged organ recovers or replaced, attacked again HIV & AIDS • Human Immunodeficiency Virus (HIV) Immune System Disorders • Allergies – Hypersensitivity to certain antigens (allergens) Æ antibodies initiate an inflammation response • Localized: hot, swelling, red, pain/itch • Respiratory: swelling restricts airway • Systemic: dilation of many arteries Æ Ø blood pressureÆ anaphylactic shock – Delayed inflammation initiated by T-cells • Poison oak Immune System Disorders • Immunodeficiency diseases – Immune cells destroyed or inactivated Æ body vulnerable to broad-spectrum of secondary infections – Immunosuppression therapies – Bone marrow disease – Severe combined immunodeficiency disease (SCID) – Acquired immune deficiency syndrome (AIDS) HIV & AIDS • Stages of HIV infection: – Infects CD4 Helper T-cells – CD4 cells turned into virus factories; no longer function to activate immune responses • HIV infection eventually results in AIDS – Syndrome symptoms: • Extreme loss of weight • Cancerous blotches on the skin • Opportunistic infection with anything • Persistent fevers and night sweats • Chronically swollen lymph nodes • Extreme fatigue Heyer CDC (2008) >56,000 new HIV cases reported per year, ~15,000 AIDS deaths per year in USA. Pandemic: >2.1 million people died of AIDS over the past 25 years globally. 4 ...
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This note was uploaded on 09/02/2011 for the course BIOL 11 taught by Professor Heyer during the Fall '08 term at UCSD.

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