IMMUNIZATION

Immunization:

  • By massive immunization there is complete eradication of disease like smallpox.
  • Diseases like polio, diphtheria, pneumonia, and tetanus have been controlled in large extent.

IMMUNITY:

  • The overall ability of the host to fight the disease causing organism by immune system is called immunity.
  • There are two types of immunity:
    • Innate Immunity.
    • Acquired Immunity.

 

Innate (non-specific) immunity:

  • Called inborn immunity.
  • Always available to protect out body.
  • This is called the first line of defense.
  • Consists of various barriers that prevent entry of foreign agents into the body.
  • If enters they are quickly killed by some other components of this system.
  • Different types of barriers are as follows:

Physical barriers:

  • Skin is the main barrier which prevents entry of micro-organism.
  • Mucous coating of the epithelium lining of respiratory, gastrointestinal and urinogenital tracts helps in trapping microbes.

Physiological barriers:

  • Acidity of the stomach kills most ingested microbes.
  • Lysozyme in tears, saliva, and snot kills bacteria by digesting bacterial wall.
  • Pyrogen released by WBC raise body temperature to prevents growth of microbes in out body.
  • Interferon induces antiviral state in non-infected cells.

Phagocytic barrier:

  • Polymorpho-nuclear leukocytes (PMNL-neutrophils), macrophages, and natural killer cells in the blood and tissues kill pathogen by phagocytosis.

Inflammatory barrier:

  • When there is injury to the tissue there is release of histamine and prostaglandins by the mast cells.
  • Due to vasodilation there is leakage of vascular fluid containing serum proteins with antibacterial activity.
  • Further there is influx of Phagocytic cells into the affected area.

Acquired (specific) immunity:

  • It is also known as adaptive immunity.
  • This immunity developed after birth when encountered with pathogen.
  • It supplements the immunity provided by the innate immunity.

 

  • Acquired immunity has following unique features:
    • Specificity: distinguish specific foreign molecules.
    • Diversity: recognize vast variety of foreign molecules.
    • Discrimination between self and non-self: it is able to recognize and respond to molecules that are foreign or non-self. It will not respond to our own cell or molecules.
    • Memory: after responding to the foreign microbes and elimination, this immune system retains the memory of that encounter (primary immune response). The second encounter with the same microbe evokes a heightened immune response. (Secondary immune response)
  • Acquired immunity is carried out by two special types of lymphocytes:
    • B-lymphocytes.
    • T-lymphocytes.
  • The B-lymphocytes produce a group of proteins in response to pathogen into the blood to fight with them calledantibody.
  • T-lymphocytes do not produce antibody but help B-cells to produce them.

Structure of antibody:

  • Each antibody has four polypeptide chains.
  • Two small chains called light chains.
  • Two longer chains called heavy chains.
  • Antibody represented as H2L2.
  • Different classes of antibody produced in out body are IgA, IgM, IgD, IgE and IgG.

AMI vs. CMI:

  • Immune response by the B-cells by production of antibody is called Antibody mediated immune responseor humoral immune response.
  • Immune response by T-cells is by activation of cytotoxic killer cells which detects and destroys the foreign cells and also cancerous cells called cell mediated immune response.
  • Rejection of organs transplants are due to T-lymphocytes.
  • Tissue matching, blood group matching are essential for organ transplantation.
  • Even after tissue typing immune-suppressants is required before and after transplantation.

 

Active immunity:

  • When the host is exposed to antigens, which may be in the form of living or dead microbes or other proteins, antibodies are produced in the host body.
  • Active immunity is slow and takes time to give its full effective response.
  • Injecting microbes deliberately during immunization or infection of microbes naturally induce active immunity.

Passive immunity:

  • Ready made antibodies are directly given to protect the body against foreign agents.
  • Colostrums of mother contain abundant antibody (IgA) to protect the child.
  • Foetus receives some antibody (IgG) from mother during pregnancy.

Vaccination and Immunization:

  • The principle of immunization or vaccination is based on the property of ‘memory, of the immune system.
  • In vaccination, a preparation of antigenic protein of pathogen or inactivated/weakened pathogen (vaccine) is introduced into the body.
  • The antibodies produced in the body against vaccine, (antigen) would neutralize the pathogenic agents during actual infection.
  • The vaccines also generate memory B and T-cells that recognize the pathogen quickly on subsequent exposure.

Passive immunization:

  • Preformed antibody or antitoxin injection for specific antigen.
  • Injection of antivenin for snake bite to counter the snake venom

Vaccine production:

  • Recombinant DNA technology has allowed the production of antigenic polypeptide of pathogen in bacteria and yeast.
  • Vaccine produced by this approach allows large scale production of antigen for immunization. E.g. hepatitis-B produced from yeast.

Allergies:

  • The exaggerated response of the immune system to certain antigens present in the environment is called allergy.
  • The substance to which such immune response is produced is allergen.
  • IgE is produced during allergic reactions.
  • Common allergens are dust, pollen, animal dander etc.
  • Common symptoms are sneezing, watery eyes, running nose etc.
  • Allergy is due to release of histamine and serotonin from the mast cells.
  • Drugs like anti-histamine, adrenalin and steroid quickly reduce symptoms of allergy.

Auto immunity:

  • Memory based acquired immunity able to distinguish foreign molecules or cells (pathogen) from self-cells.
  • Sometimes due to genetic and other unknown reasons the body attacks self cells. This results in damage to the body cells and is called auto-immune disease. E.g. Rheumatoid arthritisMultiple sclerosis.

Immune system in our body:

  • The immune system consists of
    • Lymphoid organs
    • Lymphoid tissues
    • T and B-cells.
    • Antibodies.
  • Immune system recognizes the foreign antigens, responds to them and remembers them.
  • The immune system also plays important role in:
    • Allergic reaction
    • Auto immuno diseases and
    • Organ transplantation.
  • Primary lymphoid organs: bone marrow and thymus, production and maturation of lymphocytes take place.
  • Secondary lymphoid organs: spleen, tonsil, lymph node, Payer’s patches of small intestine and appendix, where proliferation and differentiation of lymphocyte take place.
  • Bone marrow is the main lymphoid organ where all blood cell including lymphocytes are produced.
  • Thymus is a bilobed organ located near the heart, beneath the breastbone.
  • B-lymphocytes are produced and matured in bone marrow.
  • T-lymphocytes are produced in bone marrow but matured in thymus.
  • The spleen
    • Large bean shaped organ mainly contain lymphocytes and phagocytes.
    • Acts as a filter of the blood by trapping blood-borne micro-organisms.
    • Spleen is also serves as the large reservoir of erythrocytes.

 

  • Lymph node:
    • Small solid structure located at different points along the lymphatic system.
    • Traps the micro-organisms or other foreign antigens.
    • Antigen trapped into the lymph node responsible for activation and differentiation of lymphocytes and cause immune response.
  • Mucosal associated lymphoid tissues (MALT):
    • Located within the lining of major tract (respiratory, digestive and urinogenital tracts)
    • It constitutes 50% of lymphoid tissues.

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