Characterization of in vivo S typhimurium-mediated DNA gene transfer to APCs in orally vaccinated mice. Expression of GFP, naturally emitting green fluorescence, was determined by flow cytometry in total spleen cells from mice receiving the S typhimurium SL7207 strain carrying either the expression vector pASV2 (A, D, and F) or pEGFP-C2 (B, C, E, G, and H), which contain the GFP coding gene under the control of either a constitutive prokaryotic or eukaryotic promoter, respectively. Spleen cell subsets expressing GFP were identified by two-color fluorocytometric analysis after staining with biotinylated anti-CD11c, anti-F4/80, anti-B220, and anti-Thy1.2 followed by PE-Streptavidin. (C) and (D) display GFP expression by cells gated as positive for CD11c marker; (E) and (F) display GFP expression by cells gated as positive for F4/80 marker; (G) and (H) display GFP expression by cells gated as positive for B220 and Thy1.2, respectively. Control samples stained with appropriated biotin-conjugated isotype-matched negative control MoAbs followed by PE-Streptavidin were included for gate setting.