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Immune System Basics MHC 1 Antigens Immunity: The capacity to resist infectious pathogens. Pathogens: Disease-causing organisms Self vs. Non-self recognition Major Histocompatibility Complex (MHC 1) Antigen- a particle or piece of pathogen an immune system recognizes as foreign. 1st Defense: Non-specific Immune System Reacts immediately after infection- does not need to ID pathogen. 1. Barrier Defenses: Skin and Mucous membranes 2. Inflammatory Defenses: Histamine is released at the sign of damage Blood vessels leak fluid and WBC’s 3. Cellular and Molecular Defenses: 1. Macrophages: Use pocket transport (phagocytosis) to destroy foreign particles. 2. Natural Killer Cells (NK): Release hydrolytic enzymes onto target cells to rupture/destroy them. 3. Interferon 4. Complement Final Defense: Specific Immune System Recognizes pathogens and develops a sustained immune response. Comprised of two parts: 1. Cell- Mediated Response 2. Humoral Response White blood cells characters (lymphocytes): Helper T cells (Th) Killer T cells (Tc) B cells Macrophage Specific Immunity- The Battle Begins! Macrophages search body tissues for pathogens. Consume pathogens with phagocytosis, kill it with lysosomes, and save the antigens. Antigens placed into MHC 2 receptors and displayed on macrophage’s membrane. The macrophage is now considered an antigenpresenting cell (APC). http://www.youtube.com/watch?v=eVLO6j6Ho64 QuickTime™ and a decompressor are needed to see this picture. Specific Immunity Cont. Macrophage chemically signals Helper T to attach to it. Helper T attaches to the MHC 2 receptor (with foreign antigen stuck in it) with its CD4 receptor. Helper T cells have incredible variety of receptors that act like a “lock and key” in regards to the displayed antigen. If the Helper T’s “key” fits the displayed antigen’s “lock”, the Helper T is activated. Activation results in Helper T releasing cytokines (ex. Interleukin)- chemicals that cause lymphocytes to start mitosis. Fig. 43-17 Antigenpresenting cell Peptide antigen Bacterium Class II MHC molecule CD4 TCR (T cell receptor) Helper T cell Humoral immunity (secretion of antibodies by plasma cells) Cytokines + B cell + + + Cytotoxic T cell Cell-mediated immunity (attack on infected cells) Cell-Mediated Response Seek and Destroy Body cells can be infected by viruses that will hide inside the cell. As the virus reproduces inside cells, pieces of it fall off and are put into new MHC 1 receptors that the cell puts on its own membrane. Killer T cells can bind to an infected cell’s MHC 1 receptors with their CD8 receptors. If Killer T binds to MHC 1 receptors with antigen attached, it releases a chemical called perforin. Perforin ruptures the infected cells membrane and exposes the virus to other immune cells. http://www.youtube.com/watch?v=1tBOmG0QMb A&feature=related Fig. 43-11 Top view: binding surface exposed to antigen receptors Antigen Class I MHC molecule Antigen Plasma membrane of infected cell Fig. 43-18-3 Released cytotoxic T cell Cytotoxic T cell Perforin Granzymes CD8 TCR Class I MHC molecule Target cell Dying target cell Pore Peptide antigen Fig. 43-12 Infected cell Microbe Antigenpresenting cell 1 Antigen associates with MHC molecule Antigen fragment Antigen fragment 1 Class I MHC molecule 1 T cell receptor (a) 2 2 Cytotoxic T cell Class II MHC molecule T cell receptor 2 T cell recognizes combination (b) Helper T cell Humoral System Bring in the artillery! B cells have receptors called antibodies (100,000/cell). Different B cells have uniquely shaped antibodies that match specific antigens. If a B cell’s antibody is able to bind with a specific antigen (lock and key effect), the B cell receives a message from Helper T’s to become activated. Activated B cells divide into Plasma B and Memory B cells. http://www.youtube.com/watch?v=iDYL4x1Q6uU &feature=related Humoral System Cont. Plasma B cells produce and secrete 10,000 “keyed” antibodies per hour. Due to their shape, each can bind to several antigens at once. Antigen/Antibody binding has three effects. Neutralization Macrophage signaling Complement pore formation http://www.youtube.com/watch?v=lrYlZJiuf18&feature=fvw Fig. 43-21 Viral neutralization Opsonization Activation of complement system and pore formation Bacterium Complement proteins Virus Formation of membrane attack complex Flow of water and ions Macrophage Pore Foreign cell Memory B cells These cells do not actively produce antibodies Instead, they remain in the bloodstream and maintain their cell life cycle independently from Th commands. If the same pathogen/antigen complex presents itself in the future, these cells are already activated and ready to produce antibodies. There are also Memory versions of Th and Tc cells that serve a similar function.