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Biology 201 Fundamentals of Biology II Rob Mustard Adjunct Faculty PALOMAR COLLEGE Leukocytes & Immune Response Blood cells are one of the “fluid” Connective Tissues Red blood cells (erythrocytes) Mammalian RBCs lack nuclei and mitochondria ~7 m diameter White blood cells (leukocytes) Giemsa stain to differentiate WBCs 6-7 million erythrocytes / ml3 7,000 leukocytes / ml3 PALOMAR COLLEGE Immune Response Modes Innate Immunity Rapid (and general) response to a broad range of microbial invasion Acquired (Adaptive) Immunity Secondary (and highly-specific) response to previously-encountered pathogens Vertebrates have both forms of immuneresponse mechanisms PALOMAR COLLEGE Innate Immunity External defenses include: Skin: impenetrable to most viruses & bacteria Mucous: viscous fluid that traps microbes Cellular secretions: sebaceous (oil) & sweat glands reduce skin’s pH to 3-5; lysozyme digests Gram + cell walls Internal defenses begin after bacteria invade, typically through a break in skin or other epidermal layer PALOMAR COLLEGE Inflammatory Response Tissue damage from physical injury leads to cascade of chemical signals Histamine, stored in mast cells in connective tissue Nearby capillaries become dilated and leaky, allowing passage of macrophages and increased blood flow Increased local blood supply leads to redness, heat and swelling (inflammation) Macrophages move out into damaged tissues, in interstitial spaces between cells Nonspecific Inflammatory Response PALOMAR COLLEGE Leukocytes Involved in Innate Immunity: Phagocytes Neutrophils 60-70% of all leukocytes, live only a few days Big: 12-15 m (2x erythrocytes) Nucleus has 2-5 lobes (polymorphic) Neutrophils are granular Monocytes 5% of all leukocytes Biggest: 20 m Lighter, “frothy” horseshoeshaped nucleus Monocytes are agranular PALOMAR COLLEGE Leukocytes Involved in Innate Immunity: Phagocytes Eosinophils Rare in blood smears (2-4%) Big: 12-15 m (same size as Neutrophils) Nucleus has 2 lobes Dendritic Cells Patrol Eosinophils are granular interstitial spaces of skin & mucosal membranes Phagocytize invaders, process & present antigen material (APCs) Activate acquired immune system PALOMAR COLLEGE Leukocytes Involved in Innate Immunity: Hypersensitivity Basophils Rarest of the leukocytes (<0.5%) 10-12 m diameter Respond to allergic reactions (e.g., bee & wasp stings, pollen) Very granular; nucleus often obscured Live for about 2 weeks Basophils are very granular PALOMAR COLLEGE Leukocytes Involved in Innate Immunity: Cytotoxicity Natural Killer Cells A specialized lymphocyte Attack virus-infected cells Attack cancer cells (tumors) NK cells recognize infected/defective cells via surface features Bind to target cells, release chemicals (perforins) that lead to apoptosis An NK cell (N) attached to a "target" cell "T". The NK cell will kill the now helpless target cell quickly, by the injection of deadly perforin. PALOMAR COLLEGE Leukocytes Involved in Acquired Immunity Lymphocytes Very common in blood; 20-40% of WBCs Slightly larger than RBCs (~10 m) Dark-staining, circular nucleus Agranular; cytoplasm is transparent PALOMAR COLLEGE Lymphocyte Specialization Vertebrate lymphocytes take on specialized roles Circulate through blood & lymph, concentrated in spleen & lymph nodes B & T cells bear ~100K antigen receptors (all the same) Antigenbinding sites IgM Receptors Variable regions Light chain C C B cell Heavy chains Constant regions chain PALOMAR COLLEGE V V C C b chain T cell Acquired Immunity Responses Humoral Response Dendritic cell (APC) engulfs pathogen, presents antibody via cell-surface protein (MHC class II) Helper T cell binds to presented antigen APC releases cytokines to stimulate production of more “activated” T cells Activated B cells secrete antibodies, which immobilize pathogens, marking them for destruction by macrophages Cellular Immune Response A cell other than a leukocyte takes up and kills a microbe, presents antigen on surface (MHC class I) Cytotoxic (activated) T cell binds to presented antigen, releases perforins, lyses infected cell PALOMAR COLLEGE Questions?? PALOMAR COLLEGE