Antibodies for various tests can be pro-duced in a number of different ways, and we will discuss the prototype of each in turn.
a. Polyclonal antibodies: Many mammals have been used to produce antibodies, ranging from the horse, sheep, and goat down to mice and guinea pigs. Often an animal species is selected for antibody production because it will produce less-cross-reactive antibodies to a given tis-sue. Larger mammals, such as goats and sheep, are used to obtain larger volumes of serum to be used therapeutically in humans. A recent fear has been that ani-mals such as sheep or cows may have eaten animal foddage contaminated with prion disease. Thus, polyclonal antibody production for therapeutic uses has often been limited to countries like Australia or New Zealand where there have been no recorded cases of prion disease in mammals.
b. Monoclonal antibodies: Over the past two decades, the revolutionary experi-ments of Kohler and Milstein have been a major advance in the production of antigen-specific antibodies. In brief, the key to this remarkable advance was the ability to obtain spleen cells from mice that had been immunized with a given antigen and fuse these cells to a non-secreting myeloma cell line, which then produces a single antibody clone when fused with a given B cell pres-ent in the spleen cells. Antibody clones are only produced when the mouse B cell fuses with the myeloma line. Non-fused B cells are eliminated by a spe-cial factor in the medium. The beauty of the hybridoma (fused) cell is that it produces only the antibody of a single mouse B cell and is therefore identical throughout its variable and constant regions, and the antibody reacts only with a single determinant on a given antigen. Finally, it is immortal and will produce the same specificity of antibody for generations. Large-scale culture of these antibodies can provide large quantities of antibody that are precise in their reactivity.
However, a word of caution is war-ranted. These hybridoma clones can some-times partially lose their antibody produc-tion so that they no longer secrete as much antibody as before and may even stop production altogether. Finally, they may also lose their specificity so that a given hybridoma line must be checked periodi-cally against the original antigen to deter-mine whether production or specificity remains the same as the original clone. They may be “humanized” by the introduction of human heavy and light chains so that they can be used as thera-peutic agents in many human diseases, ranging from rheumatoid arthritis to many forms of cancer.