ULBP molecules are expressed by PB cell subpopulations of healthy donors. (A) FACS analysis of PB cells from healthy donors after staining with mAbs for ULBP1 (shaded curve), ULBP2 (thin solid line), or ULBP3 (bold solid line) or with secondary FITC-labeled goat anti–mouse IgG alone (dotted line). PB cell subpopulations, indicated above each histogram, were distinguished with mAbs specific for lineage markers. Analyses of monocytes and granulocytes in 2 healthy donors with ULBP-positive (N1) and ULBP-negative (N2) phenotypes are shown. Also shown is the expression of ULBP1 by N2 monocytes stimulated with growth factors (GFs; FL, SCF, GM-CSF) or GFs with IFN-γ. (B) Real-time RT-PCR analysis of ULBP1 (U1), ULBP2 (U2), and ULBP3 (U3) mRNA levels in B cells, monocytes, and T cells purified from 2 to 4 donors, as indicated by the number of diamonds. Dotted line marks the upper limit of 40 amplification cycles. Threshold cycles indicates number of cycles at which the amount of PCR product passed the threshold of detection; C, control mRNA of HPRT; nd, not detectable.