Antibodies are proteins produced by the B lymphocytes of the immune system in response to foreign proteins, called antigens
- antibodies function as markers, binding to the antigen so that the antigen molecules can be recognized and destroyed by phagocytes
- part of the antigen that the antibody binds to is called the epitope
- a short amino acid sequence that the antibody is able to recognize
Monoclonal antibodies (mAb) are important reagents used in biomedical research, in diagnosis of diseases, and in treatment of such diseases as infections and cancer
- mAb are produced by cell lines or clones obtained from animals that have been immunized with the substance that is the subject of study
- two features of the antibody-epitope relationship are key to the use of monoclonal antibodies as a molecular tool
- specificity
- the antibody binds only to its particular epitope
- sufficiency
- the epitope can bind to the antibody on its own, i.e. the presence of the whole antigen molecule is not necessary
- every B cell in an organism synthesizes only one kind of antibody
- in an organism, there is an entire population of different types of B cells and their respective antibodies that were produced in response to the various antigens that the organism had been exposed to
- in order to be useful as a tool, molecular biologists neeed substantial amounts of a single antibody (and that antibody alone)
- require a method of culturing a population of B cells derived from a single ancestral B cell, so that this population of B cells would allow us to harvest a single kind of antibody
- this population of cells would be correctly described as monoclonal, and the antibodies produced by this population of B cells are called monoclonal antibodies (mAbs)
- contrasts with antibodies obtained from the blood of an immunized animal which are called polyclonal antibodies
- to produce the desired mAb, the cells must be grown in either of two ways:
- by injection into the abdominal cavity of a suitably prepared mouse or by tissue culturing cells in plastic flasks
- mouse method
- is generally familiar, well understood, and widely available in many laboratories; but the mice require careful watching to minimize the pain or distress that some cell lines induce by excessive accumulation of fluid (ascites) in the abdomen or by invasion of the viscera
- the tissue-culture method
- would be widely adopted if it were as familiar and well understood as the mouse method and if it produced the required amount of antibody with every cell line; but culture methods have been expensive and time-consuming and often failed to produce the required amount of antibody without considerable skilled manipulation. However, culture methods are now becoming less expensive, more familiar, and more widely available
- further processing of the mouse ascitic fluid and of the tissue culture supernatant might be required to obtain mAb with the required purity and concentration