Determination of functional viral titer (TU/ml) using the ZMC p24 Antigen ELISA

There are approximately 2000 molecules of p24 per physical particle(PP) of lentivirus:
(2 x 10 3 ) x (24 x 10 3 Da of p24 per PP), 48 x 10 6 /Avogadro = (48 x 10 6 ) / (6 x 10 23 ) = 8 x 10 -17 g of p24 per PP,
approximately 1 PP per 1 x 10 -16 g of p24, 1 x 10 4 PP per pg of p24

A reasonably well packaged, VSV-G pseudotyped lentiviral vector will have an infectivity index in the range of 1 TU per 1000 physical particles (PP) to 1 TU per 100 PP (or less). Thus, the range is approximately 10 to 100 TU/pg of p24. It is through this conversion that TU/ml is obtained.

This conversion is derived from Didier Trono to determine the relationship between
pg/ml p24 and viral titer or MOI and can also be found on the Sigma Aldrich FAQ site.