FIG. 3.

FcγR-mediated gene transfer by neutralized Ad-immune complexes. An Ad vector expressing the β-galactosidase transgene (Adβgal) was mixed with various concentrations of human serum (0.01% to 10%) containing anti-Ad neutralizing antibodies (titer, 2,560). After 5 min, the Adβgal-serum mixture was applied to monolayers of naive A549 cells or A549 cells previously infected with either AdNull or AdFcγR. β-Galactosidase activity was assayed after 24 h and normalized to cellular protein content (relative light units per milligram of protein). Data were normalized to Adβgal infection in the absence of serum for each target cell type (dashed line at y = 1.0). The IC₅₀ was determined as the concentration of serum that resulted in a 50% decrease in β-galactosidase gene expression (dotted line at y = 0.5). Comparable dose-response curves were obtained in the presence of neutralizing serum during infection of either naive or AdNull-infected A549 cells, In contrast, addition of neutralizing serum during infection of AdFcγR-infected A549 cells shifted the dose-response inhibition curve, resulting in a higher IC₅₀.