Pseudotyped viruses.

Morbillivirus F and H expression constructs with truncated cytoplasmic tails (ΔF/ΔH [30 and 24 aa, respectively]) were cloned and used for pseudotype production and quantitative entry experiments as described previously (30). Briefly, HEK293T cells were plated for pseudotype production at a density of 7.5 × 10⁵ cells per well in 6-well dishes and were transfected the following day with 3.5 µg of each of the pcDNA3.1-ΔF/ΔH constructs, as well as with 1.5 µg of p8.91 (encoding HIV-1 gag-pol) and 1 µg of CSFLW (the luciferase reporter expressing the lentivirus backbone). Matched cognate combinations of F and H from PPRV and MeV strains were used in all assays. Supernatants containing pseudotyped viruses were harvested at 72 h posttransfection, clarified by centrifugation, and frozen at −80°C. Target cells were plated at a density of 2 × 10⁴ cells per well in 96-well dishes 1 day prior to transduction/infection for 72 h. Firefly luciferase activity in these cells was assayed using a luciferase assay system (Promega) according to the manufacturer’s instructions and a Promega GloMax multimode plate reader.