Antibodies produced from various sources can be used after purification as needed. Typical antibody purification methods are listed in the following.

  Ammonium sulfate precipitation is the most common method for protein purification. In solution, proteins combine with water molecules and are bonded with hydrogen. If the highly-charged ions like ammonium and sulfate be added, they would be compete with proteins for the binding site in water molecules. As a result, the solubility of the protein would be lowered to make protein molecules precipitated.
  Highly-purified ammonium sulfate is used for antibody purification and the concentration of the salt varies with species. The disadvantages of this method are low purity of the product. Thus other methods have to be performed in parallel to get highly-purified product.

  One of the structural components of cell wall of Staphylococcus aureus, protein A has a characteristic of specific binding to the Fc region of immunoglobulin G, which make it used in antibody production. However, it does not have the same affinity for all species or classes. For instance, it binds to human IgG1, IgG2 and IgG4 very firmly, but does not bind to IgG3 and it binds weakly to mice IgG1.
  Protein G, a cell wall protein of group G streptococci, can recognize the Fc region of IgG like protein A, but has different affinity. Their affinities for various immunoglobulins are shown in the following table.

  This is a very useful method to purify antigen-specific antibodies. After the mixture's passing through pure antigen beads covalently bonded to solid supporting block, wash out unbounded antibodies, and elute antigen-specific antibodies.

  The major advantage of this method is that it is possible to purify the specific antibodies concerned even from the very complex mixtures. However, large amount of antigen is required and loss of activity can occur in the elution process.

  Since various methods of antibody purification have their own strengths and weaknesses, we can adopt a couple of methods in parallel according to our purpose, the origin and type of antibodies. The advantages and disadvantages of each method are summarized in the following table.