Lecture 9 Immunity PDF

Biology Lecture 9 : Immunity Pathogens :  Pathogens : Usually microorganisms cause diseases in hosts.  Host : Organism that invaded and often harmed by a pathogen.  Pathogens include bacteria, protists, fungi and other infectious organisms , found in food and water, on surfaces, and in the air. I...

Biology Lecture 9 : Immunity Pathogens :  Pathogens : Usually microorganisms cause diseases in hosts.  Host : Organism that invaded and often harmed by a pathogen.  Pathogens include bacteria, protists, fungi and other infectious organisms , found in food and water, on surfaces, and in the air. Immune system :  The immune factors identify the nature of the pathogen, strengthen the corresponding cells and molecules to combat it and clear host cell damage.  Also they Remember pathogens to which it has been exposed to create a more efficient response upon re-exposure , memory can last several decades !! Immune system : Classified into innate or adaptive.  The innate immune response : Always present , Defend against all pathogens rather than focusing on specific ones.  The adaptive immune response : Stores information about past infections Immune system : Innate Immunity :  Non-specific toward a particular kind of pathogen,  Not caused by an infection or vaccination  Depends on physical and chemical barriers , (the first line of defense).  The second line of defense includes chemical signals that produce inflammation and fever responses , mobilizing protective cells and other chemical defenses. External and Chemical Barriers : 1. Protein keratin in skin resists physical entry into cells. 2. Other body surfaces, particularly those associated with body openings, are protected by the mucous membranes , the sticky mucus provides a physical trap for pathogens, preventing their movement deeper into the body. 3. The openings of the body, such as the nose and ears, are protected by hairs that catch pathogens, External and Chemical Barriers : 4. The mucous membranes of the upper respiratory tract have cilia move pathogens trapped in the mucus coat up to the mouth. 5. The acidic surface of the skin prevents bacterial growth. 6. Saliva, mucus, and the tears of the eye contain an enzyme that breaks down bacterial cell walls. External and Chemical Barriers : 7. The acidic stomach secretions kills many pathogens entering the digestive system. 8. The surface of the body and the lower digestive system have beneficial microorganisms (bacteria, archaea, and fungi) that coexist without harming the body , combating disease-causing organisms and outcompeting them for nutritional resources. Internal Defenses :  Include the inflammatory response, phagocytosis, natural killer cells, and the complement system.  WBC is nucleated, able to move using amoeboid locomotion , leave the blood to go to infected tissues.  A monocyte is a type of WBC that circulates in the blood and lymph and develops into a macrophage after it moves into infected tissue. Internal Defenses :  Macrophage is a large cell engulfs foreign particles &pathogens.  Mast cells reside in connective tissues especially mucosal tissues , release chemicals in response to physical injury ,play a role in the allergic response  When a pathogen is recognized as foreign, chemicals called cytokines are released , is a chemical messenger that regulates cell differentiation (form and function), proliferation (production), and gene expression to produce a variety of immune responses.  Cytokines released from WBC after pathogen recognition, also released by the infected cells. Inflammation :  The cytokines encourage inflammation.  Inflammation is a response to physical trauma, chemical irritation, and infection by pathogens (viruses, bacteria, or fungi).  The chemical signals that trigger an inflammatory response enter the extracellular fluid and cause capillaries to dilate (expand) and capillary walls to become more permeable.  The serum and other compounds leaking from capillaries cause swelling of the area ( in turn causes pain !! ). WBC :  Various kinds of WBC are attracted to the area of inflammation , depending on the nature of the injury or infecting pathogen  Neutrophil is an early arriving engulfs and digests pathogen ,followed by macrophages  Cytokines increase the core body temperature, causing a fever.  The elevated temperatures of a fever inhibit the growth of pathogens and speed up cellular repair processes.  Only dangerously high fever should be suppressed !! WBC : Natural Killer Cells (NK) : The only lymphocytes of the innate immune system , can kill cells infected with viruses or cancerous cells. NK cells identify intracellular infections, especially from viruses, by the altered expression of major histocompatibility class (MHC) I molecules on the surface of infected cells , unhealthy cells display an altered MHC class I complement on their cell surfaces. It induces programmed cell death, or apoptosis. Phagocytic cells then come and digest the cell debris Complement System :  Approximately 20 types of proteins.  Activated by infection or the activity of the cells of the adaptive immune system and functions to destroy extracellular pathogens.  Liver cells and macrophages synthesize inactive forms of complement proteins continuously.  Certain complement proteins can combine to open pores in microbial cell membranes and cause lysis of the cells. Immune system : Adaptive Immunity :  Specific to substances and organisms that do not belong in the body.  Takes longer time to respond  Has a memory system that allows it to respond with greater intensity even after year Immune system : Adaptive Immunity :  The adaptive, or acquired, immune response takes days or weeks to become established , more specific to an invading pathogen.  Occurs after exposure to an antigen either from a pathogen or a vaccination.  Activated when the innate immune response is insufficient to control an infection.  Require information from the innate immune system. Immune system : Adaptive Immunity :  Two types  Cell-mediated immune response : Controlled by activated T cells which target infected cell,  Humoral or antibody- immune response Controlled by activated B cells and antibodies.  Involves a memory give the host long-term protection from reinfection with the same type of pathogen on re exposure Immune system : B and T Cells :  Types of lymphocytes  B cells mature in the bone marrow  T cells mature at thymus ,  Becoming immuno-competent ,then migrate to the spleen and lymph nodes remain until called during an infection Humoral (or Antibody)-Mediated Immune Response  B cells participate in a chemical response to antigens present in the body by producing specific antibodies  Each B cell has only one kind of antigen receptor, which makes every B cell different.  Immunoglobulin is a protein produced by plasma cells after stimulation by an antigen.  Occur in the blood, in gastric and mucus secretions, and in breast milk. Immune system : Antibody  Circulate in the blood stream and lymphatic system  Can bind to viruses or bacteria and interfere with the chemical interactions required for them to infect or bind to other cells.  The antigen-antibody complex stimulates the complement system  Phagocytic cells, are attracted by the antigen-antibody complexes, and phagocytosis is enhanced when the complexes are present.  Antibodies stimulate inflammation Active and passive response Active immunity : The production of antibodies by plasma cells in response to an antigen ( response to infection or vaccination). Passive immunity : Giving antibodies from an outside source : antibodies circulating in a pregnant woman's body move across the placenta into the developing fetus ,or by injecting antibodies into an individual Gives immediate protection to body Cell-Mediated Immunity  T lymphocytes are unable to recognize pathogens without assistance.  Dendritic cells and macrophages first engulf and digest pathogens into hundreds or thousands of antigens.  Then, an antigen-presenting cell (APC) detects, engulfs, and informs the adaptive immune response about an infection.  Antigen fragments will then be transported to the surface of the APC, where they will serve as an indicator to other immune cells.  Dendritic cells are located in the skin, the linings of the nose, lungs , stomach ,intestine  Macrophages also function as APCs.