PDGFR-β expression and downstream activation in LGL leukemia. (A) PDGFR-β mRNA expression levels in CD3⁻/CD16⁺/CD56⁺ NK cells from either 7 patients with NK-LGL or 7 normal controls, and in CD8⁺ T cells from either 5 patients with T-LGL leukemia or 5 normal controls, were determined by real-time quantitative RT-PCR (expressed as the ratio of PDGFR-β mRNA copies/18S control mRNA copies, *P < .05). (B) Western blot assay for PDGFR-β and autophosphorylated PDGF-β-RTK expression in immunoprecipitation samples in PBMCs from a representative patient with T-LGL or NK-LGL leukemia as well as normal controls in presence or absence of rhPDGF-BB. (C) Western blot assay for PDGFR-β and autophosphorylated PDGF-β-RTK expression in immunoprecipitation samples in PBMCs from a representative patient with T-LGL or NK-LGL leukemia in the presence of pooled patient sera with or without anti–PDGF-BB neutralizing antibody. Rabbit IgG was used for isotype control. The gels in top panels indicate autophosphorylated PDGF-β-RTK expression in the same membranes used for PDGF-βR detection (bottom panel) reblotted using anti–p-Tyr antibody (PY99).