ABSTRACT
It is sometimes easy to forget that many of the tests routinely and frequently used in both obstetrics and gynecology have an immunological basis. The ubiquitous pregnancy test, for example, now so sensitive that the woman desperate to conceive can tell whether or not she is pregnant even before she misses her period, is basically an antibody and antigen interaction (Figure 6.1). Tests for immunity to rubella, or previous exposure to a whole host of other viruses, are all based on immunological principles. In this chapter, common tests that have an immunological basis are described. Central to most modern tests, especially the sensitivity and specificity, is the monoclonal antibody. Before the advent of monoclonal antibodies, antisera for diagnostic purposes were usually raised in animals by injection of the relevant antigen, i.e. the animals were immunized with the relevant antigen (for example β-human chorionic gonadotropin (hCG)). The animals responded by making polyclonal antibodies-the resultant sera contained mixtures of antibodies from different B cell clones. Although these antibodies varied in the precise nature of their variable regions, they all reacted only with epitopes on the relevant antigen (monospecific reactivity). Because the antisera contained a whole host of other proteins, before use for diagnostic purposes the polyclonal antibodies would be purified by eluting them on special columns under pH conditions that allowed initial binding of antibody to antigenic epitopes, and subsequent separation when the pH and other conditions were changed.
