For HIV-1, how can I equate the amount of p24 or RT activity to infectious units?

As a rule, it is not advisable to equate p24 or reverse transcriptase activity in terms of infectious equivalents for HIV, unless repeated infectivity assays of the same stock are performed and correlated with p24 or RT levels. Although the relative p24 or reverse transcriptase activity is positively correlated with virus infectivity in most cases, a true measure of virus infectivity (i.e., TCID50, plaque assay, LD50) as the basis for R & D is the most appropriate way to ensure reproducibility of results.