LCMV pseudotyped FIV requires low pH endosomes for efficient transduction. A549 cells were pretreated with 8 μm monensin or 10 mM NH4Cl to prevent endosomal acidification followed by application of FIV vectors pseudotyped with LCMV WE54, VSV-G, or amphotropic envelope. Transduction efficiencies were measured by β-gal assay and normalized to cells that received no pretreatment. * indicates P value ≤ 0.05 compared against untreated control (n = 9). Standard errors are denoted.