The term derives its name from its function as an antibody generator. therefore, it's a substance which generates an immune response. Chemically it's usually a protein, or nucleic acid, large polysaccharides or large lipoprotein complexes. They have large molecular weight, more than 10,000 daltons, with simple, repeating subunits. As a rule, they are foreign substances.
Antibodies or Immunoglobulins (lg)
the antibodies or immunolobulins show the following characteristics:
(i) These are produced in response to a " foreign substance" acting as an "antigen".
(ii) Chemically, these are glycoproteins -the globulins.
(iii) Structurally, they contain four polypeptide chains -two heavy chains and two light chains are held together by (-S-S) disulhide bonds, which in turn, are also joined to light chains by disulphide linkages.
The heavy chains are held together by (-S-S) disulphide bonds, which in turn, are also joined to light chains by disulphide linkages.
(iv) It can assume either a T-shape or Y-shape.
(v) There are five classes of immunoglobulin's -IgG (most abundant), IgM, IgD & IgE.
(vi) Antigen and Antibody bind to each other very specifically on a " lock & key" pattern.
(Note: This "Sticking together" of antigen to antibody is known as agglutination which stimulates phagocytosis by neutrophils)
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