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IMMUNITY II DR SATHYA ANANDAM ACQUIRED IMMUNITY ACQUIRED IMMUNITY • Resistance that an individual acquires during life. • 2 types : Active acquired immunity Passive acquired immunity ACTIVE IMMUNITY • Resistance developed by an individual as a result of an antigenic stimulus. • Also called Adaptive immunity. • Involves active functioning of the host’s immune system leading to the synthesis of antibodies and / or the production of immunologically active cells. • Latent phase, Negative phase, Sec. response,Immunological memory. HUMORAL IMMUNITY(ANTIBODY-MEDIATED) • Involves production of antibodies against foreign antigens. • • Antibodies are produced by B cells. • Circulating antibodies combines specifically with antigens and lead to lysis of antigen molecules, or neutralise toxins, or phagocytosed B cells that are stimulated will actively secrete antibodies and are called plasma cells. CELL MEDIATED IMMUNITY • Involves specialized set of lymphocytes called T cells that recognize foreign antigens on the surface of cells, organisms, or tissues • T cells regulate proliferation and activity of other cells of the immune system: B cells, macrophages, neutrophils, etc. • Defense against: • Bacteria and viruses that are inside host cells and are inaccessible to antibodies. • Fungi, protozoa, and helminths • Cancer cells • Transplanted tissue MECHANISM OF ACQUIRING ACTIVE IMMUNITY. Contact with Antigen (1st time) IMMUNE SYSTEM Contact with SAME antigen 2nd time B cells (Plasma cells) T cell sensitization Active Antibody Cytokines Memory cells Large number of active antibodies. Antibody 60 Antibody 40 20 Lag Antigen Time Active Immunity Time Passive Immunity A. Naturally Acquired Active Immunity: • Obtained through clinical or subclinical infection. • Antigens or pathogens enter body naturally. • Body generates an immune response to antigens. • Immunity may be lifelong (chickenpox or mumps) or temporary (influenza or intestinal infections) or No immunity against common cold virus infection • Anti bacterial immunity lasts shorter period • Premunition: (Infection immunity) Immunity to reinfection lasts as long as original infection persists (Malaria, Syphilis). ARTIFICIALLY ACQUIRED ACTIVE IMMUNITY: • Antigens are introduced in vaccines (immunization). • Body generates an immune response to antigens. • Immunity can be lifelong (oral polio vaccine) or temporary (tetanus toxoid). VACCINES Live vaccines BCG for Tuberculosis Sabin vaccine for Poliomyelitis MMR vaccine for Measles, Mumps, Rubella 17D vaccine for Yellow fever Killed vaccines TAB vaccine for enteric fever Salk vaccine for poliomyelitis Toxoids Tetanus toxoid for tetanus Diphtheria toxoid for diphtheria • Subunit vaccines • Hepatitis B CHARACTERISTICS OF LIVE AND KILLED VACCINES Live vaccine: • Initiates infection without causing injury or disease • Immunity lasts for several years. Booster doses may be required • Given intradermally or orally. Oral vaccines produce local immunity or CMI Killed vaccine: • Less immunogenic. Booster doses always required • Immunity lasts for short period • Given parenteral. Produce AMI PASSIVE IMMUNITY • Resistance transmitted to a recipient in a readymade form. • Preformed antibodies are administered. • No antigenic stimulus. • Host’s immune system is not actively involved. • No latent period or negative phase • No secondary response • Acts immediately NATURALLY ACQUIRED PASSIVE IMMUNITY: • Antibodies pass from mother to fetus via placenta or breast feeding (colostrum). • No immune response to antigens. • Immunity is usually short-lived (weeks to months). Artificially Acquired Passive Immunity: • Preformed antibodies (antiserum) are introduced into body by injection. • Immunity is short lived • Host immune system does not respond to antigens. ARTIFICIAL PASSIVE IMMUNITY Antitetanus serum (ATS) for tetanus Convalescent sera contain high levels of antibodies. Used for immunisation of measles and rubella Pooled human gammaglobulin used for immunisation against Hepatitis A Snake antivenom injection from horses or rabbits. USES OF PASSIVE IMMUNISATION i. To provide immediate short term relief in nonimmunised individuals ii. For supression of active immunity which may be injurious iii. For treatment of serious infections Active Immunity Passive Immunity Produced actively by immune system Received passively by the host Induced by infection or contact with antigens Conferred by administration of readymade antibodies Long lasting Short lived Immunity effective after a lag period Immunity immediately effective Immunological memory present No immunological memory Not applicable in immunodeficient persons Applicable in immunodeficient persons Used for prophylaxis to increase body resistance Used to treat acute infections COMBINED IMMUNIZATION • Active and Passive immunisation given simultaneously • ATS + Toxoid : prevent tetanus (Road injury) • Immunoglobulin + HDCV: Post – exposure prophylaxis (rabies) ADOPTIVE IMMUNITY • Injection of immunologically competent lymphocytes • Transfer factor: An extract obtained from immuno- competent lymphocytes (Lepr. Leprosy, candidiasis, malignancy, multiple sclerosis) LOCAL IMMUNITY • It is the resistance produced at the local site preventing the entry and multiplication • Secretory immunoglobulin (IgA) plays important role preventing the entry at the primary site. • Natural infection or live viral vaccine gives local immunity • Sabin (oral) vaccine (polio) influenza nasal spray HERD IMMUNITY • Overall resistance in a community for a specified disease • Ratio of resistant to susceptible host is important in this immunity. • It is relevant in control of epidemic diseases (Diphtheria, poliomyetitis etc.) When herd immunity is low epidemics occur Eradication of disease is dependent on development of herd immunity HERD IMMUNITY • Factors influencing: • Vaccination. • Quarantine measures. • Effect of carriers. • Environment plays major role.