Cellular expression of the luciferase reporter gene in the spleen. Sections of spleen from control-treated or PHZ-treated −4.0 TG mice were (A) stained with hematoxylin/eosin to assess cell lineage or (B) probed for luciferase expression with an antisense DIG-labeled luciferase RNA probe and counterstained with eosin. Lymphatic nodules are noted with a white arrow (A and B) and erythroid precursor cell clusters are noted with a black arrow (A and B, PHZ⁺). Hybridization to sense RNA probes gave no detectable signal (not shown).