2.3. SIV p27 ELISA and TCID50 Titre in TZM-bl Cells

Virus quantification in the culture supernatants was done by enzyme-linked immunosorbent assay (ELISA) for SIV p27 antigen using a commercial kit (Advanced Bioscience Laboratories, ABL, Rockville, MD, USA) following the manufacturer’s instructions. Supernatants with >10 ng/mL SIV p27 were pooled to make a single virus stock. The infectivity of the virus stock was assessed and the TCID₅₀ was determined in TZM-bl cells. To do this, the virus stock was inoculated at 1:5 serial dilutions in quadruplicate wells of 96-well plates containing in TZM-bl cells in the presence of 20 µg/mL of DEAE-dextran hydrochloride (Sigma-Aldrich, St. Louis, MO, USA). Virus titre was determined 48 h post-infection by measuring the level of luciferase activity expressed in infected cells. The TCID₅₀ was calculated as the dilution point at which 50% of the cultures were infected.