Antigen & Antibodies

The surface of all cells are covered with molecules such as proteins and Polysaccharides that carry out normal cellular functions.

  • These molecules are called antigens

  • The immune system can detect antigens on the surface of pathogens.

    • Immune system identifies them as “non-self” or foreign

  • During an immune response antibodies are produced which specifically bind to the antigen.

    • Antigens on the surface of your body cells do not trigger immune response.

      • These antigens are identified as “self”

Structure

  • Antibodies are also referred as immunoglobulins.

    • These are differnet classes of antibodies

  • Antibodies are glycoproteins consisting four poplypeptide chains

    • two long heavy chains which are identical to each other

    • two shorter light chains which are also identical to each other

    • Chains are held to each other by disulfide bridges

  • There are two antigen binding sites

    • This means one antibody molecule binds to two antigens

      • This complex is called antigen-antibody complex.

  • The tertiary structure of the antigen binding site is complementary to the structure of the antigen.

    • Meaning the antibodies are highly specific for the antigen they bind to.

  • The hinge-region is flexible

    • Allowing the distance between the 2 antigen binding sites to vary

  • The constant region has the same structure for every antibody no matter which B lymphocyte produced it.

  • The ends of the antibody molecule are different.

    • These are called variable regions

    • They form the antigen binding sites.    

    • The shape is diiferent depending on which B lymphocyte produced it

Role of antibody

  • Antibodies are produced by B lymphocytes

  • Role of antibodies in immune system is referred to as humoral immunity.

  • Antibodies act as opsonins tagging foreign bodies for phagocytosis.

  • Antibodies can stick pathogens together which repent them from spreading around the body.

    • This is called agglutination

    • By sticking the pathogens such as viruses antibodies prevent them from invading host cells.

  • Antibodies can stick to bacterial toxins preventing the toxins from hamng body cells

    • These antibodies are called antitoxins