Interpretation of ELISA and Western Blot Assays for HIV Infection Status
Working in pairs, students use an enzyme-linked immunosorbent assay (ELISA) to screen sera for antibodies to human immunodeficiency virus (HIV). Sera that test "positive" in the ELISA are subsequently evaluated by Western blotting to determine whether the patient’s infection status is positive, negative, or indeterminate according to criteria set by the Centers for Disease Control and Prevention (CDC). Because surrogate antigens and antibodies are used in this exercise, there is no risk of infection for students or teaching personnel. The students are provided with Western blot strips to which simulated antigens have already been applied, thus eliminating safety concerns associated with gel electrophoresis, such as exposure to acrylamide and the possibility of electrical shock. The banding patterns on the strips are generated using a multi-channel manifold device rather than an electrophoretic cell so that results are highly uniform, reproducible, and simple to interpret.