Techniques for the Diagnosis of HIV Infection

Antibody assays are the most widely used methods for HIV testing because they are better suited than other methods for routine use in blood banks and screening programs. 

There is no good animal model for infection by HIV. The virus will infect several primates, but it does not produce active disease and it is not practical to use primates for propagation of the virus. The chimpanzee has been used in vaccine trials to determine whether neutralizing antibody is produced and whether the growth of the virus can be inhibited in vivo. More productive work has been done using the immunodeficiency viruses of the species (e.g., simian immunodeficiency virus in macaques, feline immunodeficiency virus in cats) to study pathogenesis and treatment of retroviral acquired immunodeficiencies. 

For primary isolation of HIV, patient peripheral blood mononuclear cells (PBMC) are collected, the usual inoculum being 106-107 cells. This is the most productive specimen, although virus has been cultured from plasma, semen, tears, saliva, breast milk, and brain tissue. The virus can be cultured from patient specimens at any time in the course of disease, during which the titer changes. Blood contains approximately 60 TCID50% (50% tissue culture infective dose) per milliliter when a person is asymptomatic, and about 7000TCID50/ml in later stages of HIV disease. 

Primary isolation of HIV is accomplished by cocultivation of patient PBMCs with uninfected donor PBMCs that have been stimulated with phytohemagglutinin (PHA) and treated with the T cell growth factor interleukin-2. Fresh PHA-stimulated donor PBMCs are added to the culture at weekly intervals growth of virus can be detected in 7-32 days depending on the titer of the virus in the inoculum. 

After several passages in cell culture, many strains of HIV can be maintained in transformed T-cell lines, most commonly Hg, HUT-78, and CEM. The monocyte line U-937 also permits growth of HIV and may be more sensitive than lymphocytes in some stages of infection. 

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