Monoclonal Antibodies
In a normal immune response, antibodies are produced by many different plasma cell populations and are thus said to be polyclonal. Although these antibodies all combine with a specific antigen, they are a heterogeneous mixture of proteins. Homogeneous antibodies can be generated through the use of cloned cell lines called hybridomas; these monoclonal antibodies represent an alternative source of passive immunization. Currently, however, these are mainly made by mouse hybridomas (and thus consist of mouse antibodies) and may sensitize other animal species.
Monoclonal antibodies are commonly used in diagnostic tests. Because they are homogeneous and specific, these antibodies can differentiate between closely related infectious agents in a manner impossible with conventional antibodies. For example, they can differentiate between the rabies viruses obtained from skunks, bats, or dogs.