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Transcript
Immune system Functions of immune system Protect against infection by microbes. Isolate or remove nonmicrobial foreign substances. Destroy cancer cells that arise in the body. Body Defense System Non- specific Passive Active ~Mechanical ~ Phagocytosis barrier ~Chemical barrier ~Blood clots ~ Inflammation Specific Humoral Cell-mediated Immune Immune Response Response (HIR) (CMIR) Body Defense System Non-specific mechanism Specific mechanism Non- specific mechanism Non-specific mechanism ~ do not depend on previous exposure ~ do not selectively protect against foreign substance a) Passive mechanism b) Active mechanism Passive mechanism Mechanical skin & epithelium, ciliated epithelium & mucus Chemical barrier acid in gastric juice, tears, sebaceous secretion, nasal secretions & saliva, acidic secretion in vagina Blood clots blood clots prevent further blood loss & entry of pathogenic microorganisms Active mechanism Phagocytosis ~ invading microorganisms are engulfed by phagocytes Phagocytosis I Chemicals released by bacterium are detected by neutrophil Plasma proteins become attached to bacterium aid identification by neutrophil & adherence of bacterium to neutrophil Neutrophil moves towards bacterium Phagocytosis II Phagosome formed by pseudopodia Phagocytosis III Lysosome fuses with phagosome and releases hydrolytic enzymes Digestion of bacterial call and absorption of products into neutrophil Phagocytes amoeboid cells attracted to damaged area stimulus for migration chemical liberated by the ruptured blood cells & tissues found in liver, spleen & lymph nodes engulf toxic foreign particles localize infection Inflammation The body’s response to injury. It involves pain, heat, redness, swelling and loss of function of the affected part. Active mechanism - Inflammation Bacteria invade the body vasodilatation of affected region blood supply reddening, swelling, temp. , pain Biological significance of inflammation enables neutrophils migrate to the destroyed area & engulf invaders. localizes the invading pathogens plasma protein i.e. fibrinogen blood clot excess tissue fluid dilute & negate potential toxic irritants Specific defense mechanism It depends upon, prior exposure to the specific foreign substances, recognition of it upon subsequent exposure, and the reaction to it. Terminologies Antigen ~ foreign body to the host Antibody ~ blood protein in response to its corresponding antigen; ~circulates in blood to attack antigen & render it’s harmless. Specific defense mechanism Toxoid ~ non- toxic protein toxin, useful in vaccines Endotoxin ~ toxic substance produced by bacteria, stay in cell wall Antitoxin ~ antibody counteracting toxin produced by specific antigen Lymphocytes ~ a variety of white blood cells Types of lymphocytes T- lymphocytes (T- cells) ~ circulate permanently in the blood once produced, ~ colonize in lymph nodes ~ for cell- mediated immune response ~ do not synthesize antibody Lymphocytes B- lymphocytes (B-cells) ~ circulate between blood stream & lymphoid organs ~ less than T- cells ~ for humoral immune response ~ able to synthesize antibodies T & B cells B cells for humoral immune response (HIR) thymus independent with finger- like projection on surface synthesize antibodies when stimulated by antigens T cells for cell- mediated immune response (CMIR) thymus dependent smooth cell surface do not synthesize antibody Humoral immune response (HIR) by B cells also called antibody- mediated immunity Clonal selection B cell proliferation plasma cells & B memory differentiation cells Humoral Immune Response (HIR) Antibody Protein in nature Synthesized by plasma cells once stimulated by antigen Ig :2 identical heavy chains (H chain ) + 2 identical light chain (L chain) A family of proteins with variation in antigen- binding capacities Humoral immune response B cells for self proteins will be destroyed during fetal life. Antigen do not provide information to plasma cells but select those which can tailor make the specific antibodies. The unique DNA base sequence in lymphocytes determine the specificity of antibody. Action of antibodies Lysis of cell membrane Agglutination Stimulation of phagocytosis Neutralization of toxins Secondary response of HIR Memory cells activate body response to second infection of the antigen Enables prompt & vigorous response in second encounter short latent period higher production of antibodies high specificity larger population of memory cells Cell- mediated immune response (CMIR) by T cells do not possess antibodies thymosin promotes T cell maturation CMIR HIR vs CMIR HIR Time course Primary response: 4-5 days Secondary response: 12 days Venue B cell : lymphoid tissues e.g. lymph nodes, liver CMIR Time course 1 - 2 days Venue T cell: circulating around Importance of HIR Antibodies ~ act against bacteria, viruses & toxic matters. Memory cells~ prevent disease. Immunoglobulins ~ replacement therapy in humoral- antibody- immunodeficiency diseases. Serum from horse~ therapy of tetanus, snake bites, rabies etc. immunoglobulins ~ prevention of graft rejection Importance of CMIR Resist infection. Induces unwanted immune response, grafts or transplants. Destroys tumour. Fast in action to combat the invading pathogens. Failure/ deficiency of CMIR AIDS Specific vs non- specific defence system Specific foreign body: act on specific substances B & T memory cell develop secondary response immunity can be established Non- specific eliminate all foreign substances nonselectively no memory cell no secondary response fight against invading substances in a fast fashion Both fight against invading foreign bodies Immunity Passive Passive immunity in infants ~ antibodies from mother fetus Artificial passive immunity ~ injection with immunoglobulin short duration Active Naturally induced ~ natural encounter long duration Artificially induced ~ immunization long duration Characteristics of active immunity Antigens are recognized by Lymphocytes first before activating the cells. Specific antigen elicit the specific antibodies production. Memory cells can be established. Naturally acquired immunity A result of contact to diseases or vaccination. Achieved injecting small amount of antigen (vaccine) into the body of an individual. The small dose of antigen is safe. The individual does not contact the disease, but is stimulated to form abtibodies against the antigen. Booster injection is needed sometimes. Vaccination Small dose of antigen is injected to the individual. either killed or attenuated ~ not contact with disease ~ stimulated to manufacture antibodies Booster injection quicker production of antibody & long lasting immunity. Types of vaccine Toxoids e.g. tetanus ~ a preparation of the poisonous material that is produced by dangerous infective organisms. Killed organisms e.g. dead influenza viruses Attenuated organisms e.g. TB, measles, poliomyelitis ~ modified but living organisms Infective agents of a related disease e.g. smallpox Duration of protection Smallpox & polio vaccines long lasting, complete protection BCG fairly long lasting, but not complete protection TAB typhoid rather temporary & partial protection Vaccines for special group Sex group Young girls : German measles Age group Young children : Polio, smallpox, measles, cough Occupation Medical workers: Hepatitis B Sewage workers, field workers: Plague Traveller Pros & cons of vaccination Pros Establishes active immunity against specific diseases Cons Induces hypersensitivity in some people Unwanted immune responses Transfusion reaction Rejection of tissue transplantation Blood transfusion If a patient receives blood that is incompatible, a type of unwanted immune response occurs. Agglutinogens( act as antigens) exist on donor’s RBC membrane. Incompatible agglutinated donor’s cell Rejection of tissue transplantation Transplantation ~ replacement of diseased tissues or organs by healthy ones Foreign tissue acts as an antigen once inserted into recipient stimulates immune response in the recipient Rejection of transplanted tissue Graft CMIR of the host Proliferation of killer cells Enhanced phagocytosis REJECTION Vascularisation between grafts & the host Methods to avoid/ minimize graft rejection Tissue matching ~ graft between genetically identical individuals are not rejected. Immunosuppressive drugs ~ any drug inhibiting mitosis suppresses the response. More prone to cancer X- irradiation ~ X -irradiation inhibits blood cell production slow down rejection Drugs used to treat infectious diseases For example: Antibiotics Sulphonamides Antibiotics ~ Organic compounds produced by microorganisms. ~ Able to kill or inhibit the activities of other micro- organisms. Action Inhibit cell wall formation Destroy the selective permeability of cell membrane Interfere protein synthesis Inhibit nucleic acid metabolism Mechanisms of antibiotic resistance Inactivation of the antibiotics Absence of sensitive structures to antibiotics Presence of barrier to protect the cell Develop alternate metabolic pathway Avoid antibiotics resistance Avoid overuse & indiscriminate use Use correct dosage of proper antibiotics Use different antibiotics once micro-organism shows resistance Use combination of antibiotics Non- medical use of antibiotics Growth stimulation ~ poultry & livestock Food preservation ~ preserve fresh meat Controlling plant diseases Sulphonamides ~ A group of chemical disturbing the metabolism of folic acid in bacteria Normal: Para-aminobenzoic acid Folic acid Normal growth of bacteria Presence of Sulphonamides: Sulpha drug no folic acid produced Bacteria will die Problems of drug therapy Induce the development of drug resistant strains of micro-organism. Cause undesirable side effects. May not be used in some patients. Eliminate the normal micro-organism in patients’ guts.