HIV infection: immunobiology and laboratory diagnosis

The immunobiology of human immunodeficiency virus (HIV) and the role of laboratory testing in the diagnosis and management of HIV infection are reviewed. HIV is one of a family of RNA viruses called retroviruses. HIV has three structural genes (one of which codes for reverse transcriptase) and six regulatory and maturation genes. Upon infection in humans, HIV commandeers the immune system by infecting and lysing T-helper lymphocytes. Since these cells are key to directing the body's immune defenses, the person becomes susceptible to a variety of opportunistic infections, neoplasias, and neurologic disorders. Laboratory tests for HIV are used for three purposes: screening of large populations (such blood donors), diagnosis of current or latent infection, and monitoring of disease progression. Diagnosis of HIV infection relies on HIV antibody detection, viral cultures, antigen detection, or polymerase chain reaction viral genome detection. Disease progression can be estimated using immunophenotyping with flow cytometry or using other immunologic markers. The immunologic variables associated with HIV infection disclose a growing spectrum of immune deficits. New tests for diagnosing and monitoring patients infected with HIV have been quickly incorporated into clinical practice.