MONOCLONAL ANTIBODY

The four-chain structure of an antibody, or immunoglobulin, molecule The basic antibody produced artificially by a genetic engineering technique. Production of monoclonal antibodies was one of the most important techniques of biotechnology to emerge during the last quarter of the 20th century. When activated by an antigen, a circulating B cell multiplies to form a clone of plasma cells, each secreting identical immunoglobulin molecules. It is such immunoglobulinsderived from the descendants of a single B cellthat are called monoclonal antibodies. The antibody response to a natural infection or an active immunization, however, is polyclonal. In other words, it involves many B cells, each of which recognizes a different antigenic determinant (epitope) of the immunizing antigen and secretes a different immunoglobulin. Thus the blood serum of an immunized person or animal normally contains a mixture of antibodies, all capable of combining with the same antigen but with different epitopes that appear on the surface of the antigen. Furthermore, even antibodies that bind to the same epitope often have different abilities to bind to that epitope. This makes isolating an appreciable quantity of a particular monoclonal antibody from the polyclonal mixture extremely difficult.