Health Information

Polymerase Chain Reaction and Screening for Human Immunodeficiency Virus

The use of the polymerase chain reaction (PCR) to amplify minute quantities of DNA has revolutionized the ability to detect and analyze DNA species. With PCR it is possible to synthesize sufficient DNA for analysis. Conventional methods for detection and identification of the human immunodeficiency virus (HIV), such as Southern blot-DNA hybridization and antigen analysis, are labor intensive and expensive and have low sensitivity. An infected individual, with no sign of AIDS (acquired immune deficiency syndrome), may test false negative for HIV by these procedures. Early detection of HIV infections in these individuals is crucial to initiate treatment and/or monitor the progression of their disease. In addition, a sensitive method is required to be certain that blood contributed by donors does not contain HIV. PCR amplication of potential HIV DNA sequences within DNA isolated from an individual’s white blood cells permits the identification of viral infections prior to appearance of antibodies, the so-called seronegative state. Current methods are too costly to apply this testing to large-scale screening of donor blood samples. PCR can also be used to increase the sensitivity to detect and characterize DNA sequences of any other human infectious pathogen.

The Nested Polymerase Chain Reaction to Detect Microchimerism

Donor leukocytes transferred to patients receiving blood transfusions have been shown to survive in the recipient’s peripheral blood. The significance, if any, of this microchimeric population of leukocytes remains to be resolved. One of the best ways to detect donor-derived cells in the recipient’s blood is to use PCR detection of polymorphisms in the HLA-DR region of the major histocompatibility complex (MHC). A nested PCR assay was at least 100-fold more sensitive than a standard PCR assay. However, because of the increased sensitivity, non-specific products may appear due to mispriming events that are generally associated with pseudogenes. As such it is essential to establish a baseline pattern with pretransfusion blood samples. Once potential false positivies could be excluded with these baseline patterns, the detection of donor leukocytes is greatly enhanced.