Chapter 43 The Body’s Defenses: The Immune System Innate Immunity Aquired Immunity Cell-Mediated Response Humoral Response Lymphatic tissues

Vertebrate Defense Mechanisms – The immune system = cellular and chemical mechanisms that protect the animal against attack by pathogens. – Animals defend themselves against intrusion by 1. potentially dangerous pathogens, including viruses, fungus and bacteria, encountered in the air, in food, and in water. 2. abnormal body cells that may develop into cancer. 1.White blood cells = leukocytes 2.Chemical messengers = cytokines

Types of White Blood Cells Nuetrophils – (60 to 70% of circulating WBC) Phagocytic, secrete antibacterial enzymes. Eosinophils – (2 to 4%) Detoxify foreign proteins and destroy parasites (ex. worms) via secretion of destructive enzymes Basophils – (0 to 1%) Release histamine which initiates inflammation. Monocytes – (3 to 8%) Become macrophage. Lymphocytes – (20 to 30%) T cells and B cells of specific immunity.

Plasma cells Differentiated B lymphocytes Secrete antibodies. Macrophages Differentiated monocytes. Phagocytic, process and present antigen, activate T cells Mast cells Similar to basophils, initiate inflammation.

The Body’s Defenses Nonspecific defense mechanisms (Innate) not selective in their response + fight off everything the same way Specific Defense Mechanisms (Aquired) Immune System + generates efficient and selective response

Nonspecific Defenses Against Infection (Innate Immunity) 1st Line of Defense physical and chemical barriers + skin and mucous membrane + acidic sweat and lysozymes

Nonspecific Defenses Against Infection 2nd Line of Defense Phagocytosis + ingestion of invading organisms by certain types of WBC - neutrophils and monocytes - eosinophils and natural killer (NK) cells Macrophages act as antigen presenting cells to activate specific immunity Neutrophils release chemicals causing widespread killing of bacteria antimicrobial proteins + complement system - serum proteins help to destroy (lyse) microbial cells + interferons - secreted by virus-infected cells + limit cell-to-cell spread of viral infection

inflammatory response + localized response to tissue damage (cut) or entry of microorganism - Histamine released by mast cell attract neutrophils and eosinophils - increased blood supply (redness/swelling/warmth) more RBC dilutes harmful substances, O 2 and nutrients - histamine and prostaglandins + aid in delivering clotting elements and phagocytic cells

Phagocyte Mobilization – Inflammatory mediators attract phagocytic cells. – Neutrophils within 1 hour; usually gone by day 3 or 4. – Macrophages within 8 to 12 hours; can last months. 1. Remove injurious agents, debris and dead cells from site. 2. Stimulate repair. 3. Activate specific immunity.

Acquired Immunity Immune System Response lymphocytes + B cells and T cells - come from stem cells in bone marrow + mature in different locations before moving on to lymphoid tissue (lymph nodes, spleen, blood, lymph) - respond to specific antigens + clonal selection - effector cells and memory cells + primary and secondary immune response self vs. non-self + autoimmune diseases - Type I diabetes, Multiple sclerosis

Three classes of lymphocytes involved in specific immunity T4 cells aka helper T cells: – needed for cell mediated and humoral immunity – develop in the thymus T8 cells aka cytotoxic T cells: – responsible for cell mediated immunity – develop in the thymus B cells aka plasma cells: – responsible for humoral immunity – differentiate into plasma cells, and produce – antibody – develop in bone marrow

Antigens Any substance capable of triggering an immune response activating lymphocytes. – Virus, bacterium, fungus, parasite, portion or product of one of these organisms, tissues or cells from another individual foreign macromolecules – proteins – strongest antigens – nucleic acids – some lipids – many large polysaccharides Generally small molecules (peptides, nucleotides) are not antigenic.

Epitope = Antigenic Determinant Macromolecules have several to several hundred different kinds of epitopes on their surface; cells can have 1000s. Some epitopes are more effective than others at stimulating an immune response.

Cell-Mediated Immune Response 43_18CytotoxicTCells_A.swf 43_18CytotoxicTCells_A.swf 1.Cells Macrophages & antigen presenting cells T4 > Helper T cells recognize class II MHC activate B & T cells, NKC, & MO T8 > Cytotoxic T cells recognize class I MHC kill viral infected, foreign & cancer cells 2. Secretions = Cytokines: Interleukins from macrophages and helper T cells differentiation and activation of T cells and B cells Perforin from cytotoxic T cells cell lysis

Cell Mediated Response 1) Pathogen is ingested and presented by macrophages in conjunctions with MHC II. Macrophages secrete interleukins. 2) T4 cell binds antigen on MHC II. Activation and clonal expansion require interleukins. Activated helper T cells secrete interleukins. Inerleukin 1 & 2

Cell Mediated cont’d 3) T8 cell activation: – T8 cells bind to antigen on MHC 1 on infected cell – Activation and clonal expansion require interleukin from helper T cells 4) Cell Lysis: – Activated cytotoxic T cells bind antigen on MHC 1 on infected cell – Secrete perforins to kill infected cell.

Humoral Immune Response 43_14RoleOfBCells_A.swf 43_14RoleOfBCells_A.swf Cells and secretions B cells display antigen with MHC II molecules Helper T cells MHC II-antigen receptors Plasma cells secrete antibodies (immunoglobulin) Interleukin from helper T cells (plus other cytokines) Antibodies inactivate the pathogen by binding to free antigens and marking them for destruction

Antibody Functions 1. Neutralization Precipitation & Agglutination Opsonization Complement fixation & Activation

Lymphatic Organs Thymus: Production & maturation of T lymphocytes Spleen: Phagocytosis of particlate matter & aged or damaged cells in blood Lymph Nodes: Expose lymph born antigens to B & T cells Tonsils: Lymph Nodes in head

Allergic Reactions & Anaphylatic Shock Allergy: Hypersensitivity certain environmental antigens = allergens IgE and mast cell activation Hayfever is a local reaction Anaphylactic shock is systemic