CHAPTER 43-THE IMMUNE SYSTEM Overview I. 2 defense systems A. Innate immunity 1. All animals 2. Born with 3. Barrier defenses a. Skin, mucous, cilia/ hair, pH 4. Internal a. Receptor proteins B. Acquired/Adaptive immunity 1. Only vertebrates 2. Adaptive/learned immunity 3. 2 nd defense  after innate

43.1- Innate Responses & Shared Traits of Pathogens I. Innate immunity of invertebrates A. Barrier defense 1. Exoskeleton 2. Lysozymes a. Digests microbial cell walls B. Internal defenses 1. Phagocytosis 2. Recognition proteins a. Unique marker molecules found only on microbes (ID tags) 1. Not found within animals b. Recognition proteins on immune response cells bind to marker molecules on microbes and destroy 3. Toll receptors a. Specific receptor proteins in invertebrates b. Through signal transduction(chpt. 11) the activated Toll receptor initiates the release of antimicrobial peptides disrupting microbial cell walls and membranes

II. Innate immunity of vertebrates A. Barrier defense B. Cellular innate defenses 1. Recognition a. Toll-like receptor (TLR) 1. Receptor protein on WBC (leukocytes) 2. Phagocytic leukocyte types a. Neutrophils 1. Blood stream 2. Attracted to infected tissues by signaling a. [ ] gradient 3. Short lived  destroy themselves in the process b. Macrophages 1. Mainly lymphatic system c. Eosinophil 1. Mainly beneath mucosal surfaces 2. Parasites d. Dendritic cells 1. Acquired immunity

C. Antimicrobial peptides & proteins 1. Interferons a. Virus defense b. Affected cells secrete interferons 1. Cause a defense response by surrounding uninfected cells to produce substances that prevent viral reproduction 2. Complement system a. Proteins in blood plasma b. Inactive 1. become active when encounter microbes c. When active causes lysis of microbes

D. Inflammatory response 1. Steps a. Injury b. Mast cells c. Macrophages d. Blood vessel dialtation & permeation e. Neutrophils

E. Natural killer cells 1. I MHC 43.2-Acquired immunity-Pathogen specific recognition I. Intro A. Lymphocytes 1. B & T cells B. Antigen 1. Recognized and elicits a response by lymphocytes 2. Recognized by antigen receptors on B & T cells a. Specific for a particular epitope 3. Epitope a. Portion of antigen that is recognized by antigen receptor II. Antigen recognition by B cells and Antibodies A. Structure

B. Function 1. Recognize and attach to free and attached epitopes 2. Once antigen is attached B cell divides forming cells that secrete antibodies a. Soluble form of receptor b. Function like the B cell however not membrane bound III. Antigen recognition by T cells A. Structure

B. Function 1. Recognize and attach only to antigen fragments that have been presented by a host cell protein a. Major Histocompatibility Complex (MHC) 1. Pathogen enters host cell 2. Host cell enzymes cleave antigen 3. MNC + Antigen fragment move to cell membrane and get presented 2. Infected cell killed by T cell

IV. B cell & T cell Development A. 4 major factors must happen in order for immunity to be acquired 1. Lymphocyte & receptor diversity a. Allows detection of never before seen pathogens 2. Self-tolerance a. Lack of reactivity against animals own cells and molecules 3. Cell proliferation a. Activation greatly increases the number of B & T cells specific for an antigen 4. Immunological memory 1. Stronger and more rapid response to an antigen encountered previously B. Generation of B & T cell diversity 1. Light chain gene a. Light chain anatomy encoded for by 3 gene segments 1. Variable segment (40) 2. Joining segment (5) 3. Constant segment (1)

b. DNA rearrangement 1. Occurs early in development 2. Recombinase a. Acts randomly joining 1/40 V with 1/5 J & 1/1 C

B. Origin of self-tolerance C. Proliferation of B & T cells 1. Clonal selection a. Effector cells 1. active immediately, short lived 2. B cells = plasma cells (antibodies) 3. T cells = helpter T cells & cytotoxic T cells b. Memory cells 1. Active immediately, long lived 2. Will give rise to effector in the future

D. Immunological memory 1. Primary immune response a. Peaks days after initial exposure 1. B & T cells give rise to effector cells 2. Secondary immune response a. Memory cells b. Peaks 2-7 days after exposure 1. Stronger, more prolonged response

43.3-Acquired immunity defends against infection of body cells & fluid I. Intro A. Humoral immune response (antibody-mediated response) B. Cell-mediated immune response II. Helper T cells: A response to nearly all antigens A. Helper T cell activated by antigen-presenting cells 1. Helper T cell goes through clonal division 2. Antigen-presenting cell & helper T cell interaction

III. Cytotoxic T cells: A response to infected cells A. Activated by cytokines from helper T cells & interactions with antigen-presenting cells 1. Eliminate infected body cells 2. Target cell & cytotoxic T cell interaction

IV. B cells: A response to extracellular pathogens A. Activated by cytokines from helper T cells & antigens B. Activation can occur w/out helper T cells

C. The role of antibodies in immunity 1. Neutralization 2. Opsonization 3. Complement & pore formation

V. Active & passive Immunization A. Active vs. Passive B. Immune rejection 43.4  Disruptions in immune system function can elicit or exacerbate disease I. Exaggerated, self-directed, & diminished immune responses A. Allergies 1. Exaggerated response 2. Anaphylactic shock B. Autoimmune disease C. Exertion, stress, and the immune system D. Immunodeficiency diseases 1. Inborn immunodeficiency 2. acquired immunodeficiency II. Acquired immune system evasion by pathogens A. Antigenic variation B. Latency C. Attack on the immune system: HIV III. Cancer & immunity