Bovine serum albumin antigenic sites

Figure 7. Structure and location of the six regions of bovine serum albumin (BSA) and of human serum albumin (HSA) that we have shown to carry antigenic sites. It Is not Implied that the antigenic sites comprise the entire size of the regions shown, but rather that they fall within these regions. Reproduced with permission from Refs. 9, 10, and 11.

Antigens not only induce an immune response, but will also react with antibodies existing in a living organism. These two properties are different. Small molecules like pesticides are not able to induce the production of antibodies. They can only react with antibodies already present. They are called haptens. To generate antibodies specific to a hapten, haptens must be covalently bonded to a protein (e.g. BSA Bovine Serum Albumin) or polysaccharide. Therefore, the hapten must have reactive sites. On the other hand, this modification in the structure must not influence the specificity of the antibodies that will be produced. 

Apply a specific antigen (Ag) solution to a microtitre plate capable of adsorbing antigens by nonspecific hydrophobic interaction. Add a non-interfering protein such as bovine serum albumin (BSA) to occupy any remaining attachment site on the plate. 

The immune system does not recognize relatively small molecules, so we must use a trick to prepare antibodies with binding sites that are specific for a particular drug. As shown in Figure 1 IF-Id, we attach the drug covalently to an antigenic carrier molecule such as bovine serum albumin (BSA), a protein that is obtained from the blood of cattle. 

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