Immunoglobulins are proteins of animal origin endowed with known antibody activity and certain other proteins related by chemical nature and hence antigenic specificity. They are found in plasma, lymph, urine, spinal fluid, saliva, tears, bile, nasal intestinal secretions, lymph nodes, spleen and bone marrow. Five classes of immunoglobulins are known; they differ in their, physicochemical properties like electrophoresis mobility, sedimentation coefficient, diffusion coefficient, molecular weight and the amino acid content. The five types are IgM, IgA, IgG, IgE and IgD. Each immunoglobulin molecule has two light chains and two heavy chains and can react specifically with the determinant group of antigen. The light polypeptide chains are common to all classes of antibodies. These are of two types: K and L. A given immunoglobulin contains either two K chains or two L chains but not one of each type.