Single-cell RT-PCR for G-CSFR expression in T cells after G-CSF treatment in vivo. T cells were freshly isolated by microbead technology (purity > 98%) and single cells were handpicked under microscopic control using a microcapillary system. The leukemia cell line U937 served as a positive control (P). The application of exon–intron spanning primers allowed the discrimination from genomic amplification (G) of the G-CSFR (top blot). Because of the coamplification of the T-cell receptor α (TCR-α) chain, the analyzed cells could be identified as T cells (bottom blot). Peripheral T cells served as a positive control. Efficiency of single-cell RT-PCR for G-CSFR and for TCR-α chain was higher than 90%. P indicates positive control; N, negative control; and G, genomic amplification.