Flow cytometric analysis of transgene expression in peripheral blood leukocytes. (A) A vav-lacZ transgenic progeny mouse (10 weeks old) and (B through F) HS21/45 vav-hCD4 mice. (B) Primary vav-hCD4 animal with intermediate expression; (C and D) mosaic primary vav-hCD4 mice; and (E and F) their respective transgenic progeny. Dotted lines with shading underneath show nontransgenic controls run in parallel. The expression oflacZ was assessed by a flow cytometric assay for β-galactosidase activity11 and of hCD4 with an antibody (see Materials and Methods). The 2 peaks in (E), which may reflect the different hCD4 levels in different cell lineages (see Table 1), were not as notable in other mice of that strain.