Immune System.docx

Immune System Dealing with pathogens and recognizing antigens What affects immune response? Age, Prior response, sex, habitat, physical response Defences: Saliva – antibacterial enzymes Tears – antibacterial enzymes Skin – prevent entry Mucus – linings trap microbes and dirt Stomach acid – low pH ki...

Immune System Dealing with pathogens and recognizing antigens What affects immune response? Age, Prior response, sex, habitat, physical response Defences: Saliva – antibacterial enzymes Tears – antibacterial enzymes Skin – prevent entry Mucus – linings trap microbes and dirt Stomach acid – low pH kills bacteria Gut bacteria – “good” gut bacteria outcompete bad Primary lymphoid organs – bone marrow, thymus Secondary lymphoid organs – lymph nodes, the spleen (produces lymphocytes, acts as blood reservoir, destroys detective RBC), tonsils and various mucous membrane layers in the body. Lymphatic system Lymph – clear fluid, open circulatory system towards the heart Filtered interstitial fluid Circulated semi-passively dependant on contraction of lymph vessels Transports WBC’s Lymph passes through lymph nodes (containing lymphocytes) where microbes and waste are filtered out Non-specific defence (exterior) “innate immunity” First line of defence Skin Mucous membranes Secretions Non-specific defence (interior) Second line of defence Phagocytic white blood cells Antimicrobial proteins Inflammatory response Neutrophil: Most abundant WBC (70%) Fight early stage of bacteria Engulf and destroy pathogens Multilobed Macrophage: Important for long-lasting infections Inactive monocytes – large tissue Pseudopodia, migration and phagocytosis Largest phagocytes, long lived Clean up dead WBCs, foreign material, cancer cells and tissue debris E.g. lung alveolar; brain microglial cells; histiocytes in connective tissues, peritoneal, red pulp of spleen Natural Killer Cells (white blood cells): Not as differentiated Involved in killing virus-infected cells, transplanted bone marrow cells and malignant tumour cells Attack cells with surface membrane change (loss of MHC I molecule) Pore insertion (perforin) Cell lysis Specific defence Third line of defence Lymphocytes Antibodies Develops shortly after birth and during first months- acquired immunity First phase (activation) & Effector phase (memory & elimination) Defence responses specific and targeted against particular pathogen Becomes more efficient with repeated attacks- memory Lymphocytes and antibodies B cells (antibody mediated immunity) T cells (cell-mediated immunity) Lymphocytes Cytotoxic-T-cells = kill virus infected and damaged cells Helper-T-cells = help cytotoxic-T-cells and B-Cells in immune response B-cells = produces antibodies Adaptive immunity: Antibody-dependent defences Antigens: All molecules and structures that can trigger a specific immune reaction Antigen receptors: Coded for by a small number of genes Genetic recombination allows millions of different receptors to be coded for Occurs in bone marrow where unspecialised cells differentiate into B lymphocytes or T lymphocytes Occurs before exposure to antigen Around 100,000 receptors per cell, specific to one antigen Response Mechanism: B cell binds to antigen via membrane antibodies Activated lymphocyte (assisted by B-cells) Transforms into plasma cell (larger) Secretion of antibodies into circulation *B-cells transform into memory cells after step 2 then lie dormant waiting for re-infection Antibody Classes: IgG (72%): Most common in blood and lymph Directly attack microbes & toxins of bacteria & increase phagocytosis Involved in fighting antigen the second time it appears Crosses placenta to protect fetus & neonate from infection IgA (8%): Two basic units Works against bacterial toxins & directly attack some microbes Most common Ab in secretions (e.g. saliva, bile, colostrum) IgM (15%): Largest antibodies circulating in blood and lymph First Ab to show up after a microbe infects & activates complement IgD (1%): Act as surface receptors on B cells together with IgM. Found primarily in blood and lymph IgE (4%): Ab binds to mast cells to facilitate inflammatory response to antigen & cause allergic reactions Acquired Immunity B-cells encountered antigens and produce antibodies Acquired immunity can be obtained artificial or natural Self vs Non-self-discrimination Have our own ‘fingerprint’ of protein & carbohydrate on surface of cells ‘MHC protein complex’ During development B & T cells exposed to MHC proteins Lymphocytes develop self-tolerance for self-antigens Failure or loss of self-tolerance= autoimmunity (i.e. production of anti-self-antibodies) eg. autoantibodies against beta cells of pancreas = Insulin dependent diabetes mellitus