Immune System

Immune System

1. Immune Response

   • Defence Mechanisms
     • Non specific
       • Physical Barrier
         • Skin
       • The Process
         • Phagocytes engulf pathogens
           • Phagocytosis
             • Phagocyte Type of WBC
             • Phagocytes eg macrophage in liver
           • Phagocyte recognises foreign by binding to receptors
             • Chemical proporties of pathogens also act as attractants for phagocytes
               • Cytoplasm of phagocyte moves around the pathogen to engulf it forming a phagosome
                 • Pathogen contained in a phagocytic vacuole in the cytoplasm
                   • Lysosome containing lysozymes fuse with P.vacuole
                     • Hydrolytic enzymes start to hydrolyse pathogen cell walls
                       • Soluble products absorbed / removed from cell by exocytosis
                         • The foreign antigens presented on its cell surface membrane
                           • Turns into Antigen-presenting cell APC
           • Antigen-presenting phagocytes activate helper T cells
             • T lymphocyte cell specific receptors bind to Antigens on the APC
               • Attachment triggers T lymph cell to divide rapidly by mitosis to form its clone
                 • Cloned T cells do many things:
                   • Activate cytotoxic T cells
                     • Kill abnormal cells (phagocytes) infected by pathogen
                       • Binds to pathogen to start cell death
                         • Produces Hydrogen peroxide OR protein (perforin)
                           • This makes holes in cell-surface membrane
                             • Resulting in cell death
                   • T helper cells
                     • Stimulate B cells
                   • T-memory cells
                     • Remembers specific antigen of pathogen
             • T lymphocytes activate B lymphocytes
               • Another type of WBC
               • B-Plasma cells release more antibodies into blood
                 • Identical to B cell (clones)
                   • Secrete many specific antibodies
                     • Monoclonal antibodies
                 • Responsible for immediate defence
                   • Production of anitbodies and memory cells
                     • Primary Immune Response
                 • B-Memory Cells keep antibodies
                   • B-memory cell remembers
                     • specific antibody for 2nd response
               • B cells covered in antibodies
                 • Antibodies bind to their specific antigens or receptors on T cell
                   • Forms antigen-antibody complex
                   • This process and helper T cells activates B cells
                     • Activated B cells divide into plasma cells
               • B cells can also be a APC
                 • Antibody on B cell surface fits to complementary foreign antigen
                   • Antigen enters B cell by endocytosis and is presented
                     • T cell binds to presented antigen
                       • Activates B cell to divide
                         • Process called clonal selection
     • Specific
       • Cell-mediated response
         • T lymphocytes (T cells)
           • Type of WBC
             • Recognising "self"
               • Fetus
                 • Lymphocytes collide with self material exclusively
                   • Any lymphocytes that receptors fit with self material die or are suppressed
               • Adult
                 • Lymphocytes produced in bone marrow
                   • They initially only encounter self-antigens
                     • Any that show immune response to self-antigens undergo apoptosis (cell death)
                       • This eliminates any clones of these before they appear in the blood
       • Humoral response
         • B lymphocytes (B cells)
   • Cell Recognition
     • Antigens
       • Proteins
         • Variety and specific structures cause many combination
       • Membrane-bound protein, WBC can identify antigens determine self or foreign
     • Identifying the body's own cells and molecules
       • "self"
     • Identifiying foregin cells and molecules
       • "non-self"
   • Foreign antigens trigger an immune response

2. Antibodies

   • Protein with quaternary structure
     • Arms of antibodies bind to antigens of different pathogens
       • Clumps pathogens together (agglutination)
         • Effective as
           • Limits the spread of the pathogen
             • Spread of pathogen around the body
           • Clumps for effective phagocytosis