Detection of β-gal expression in TPA-stimulated HEL cells. LacZ was driven by cytomegalovirus (CMV) (A and B) or −245 bp hPF4 promoters (C and D). (A) X-gal staining (positive cells blue); (B) IGSS staining (positive cells brown); (C) IGSS staining; and (D) negative control, IGSS with no primary antibody (no brown signal). Original magnification × 500.