Quantitative Assays for Virus Infectivity

The infectivity assay is used to titrate virus-containing clarified culture supernatant fluids to determine the 50%-tissue culture infective dose (TCID50) of HIV-1 per ml of original fluid. The ability to measure the amount of infectious virus present in virus-containing fluid is important and useful, particularly for determining the input multiplicity of infection for antiviral experiments [1]. It is a more sensitive and specific assay of virus infectivity than the determination of HIV-1 p24 antigen production or RT activity, as the latter values may also include the measurement of defective virions. This assay can be modified for use with different viral isolates and different cell types.