ABSTRACT
Methods for measuring antigen-antibody reactions have been well established and include those that have direct biological relevance (Table 1). Other assays have been developed which provide specific qualitative and quantitative measurement of Ag or Ab for both research and diagnostic purposes. Since the immune system recognizes and remembers virtually all Ags that are introduced into an individual, assays which demonstrate the presence of Ab to an organism in the serum of a patient have become a standard way of determining that the patient has had contact with, was infected by, the organism (e.g., the presence of Ab to HIV in the serum of a patient usually means that the patient has been infected with HIV). Alternatively, Abs with defined specificity (e.g., to Ags associated with cancer cells) can be used to determine the presence of disease in a patient. Abs are also extremely important tools in molecular and cellular research as they permit the localization and characterization of Ags.
