Till date, there are 5 types of antibodies in the human body, which are well studied. They are distinguished on the basis of presence of peptide chains (light chain & heavy chain). Types are :
(1) IgA : It contains alpha heavy chain. It is present in colostrum, and has an important role in passive immunisation of infants, exists as dimer. Also secreted through tears & saliva. Plasma level is around 13%.
(2) IgD : It is formed of delta heavy chain. It serves as B cell receptors.
(3) IgE : Formed of epsilon heavy chain. It is present in scarce in the plasma, it is the antibody of allergy, generally binds to basophils and mast cells.
(4) IgG : Formed of gamma heavy chain. It is abundant in the plasma (80%), and also the smallest in size. Due to its smaller size, it can pass through placental barrier and provides passive immunisation to the foetus. Generally binds with phagocytes. Neutralises toxins and carries opsonization. Responsible for erythroblastosis foetalis in Rh - mother.
(5) IgM : Formed of mu heavy chain. Largest of all, serves as B cell receptors. It is the main antibody for primary response. Present in plasma around 6%.