To further examine the cause of this signaling pathway deregulation, we measured mRNA and protein expression levels by real-time PCR and Western blots, respectively, of four negative regulators of the IL-2R signaling pathway including src homology 2 (SH2)-containing phosphatase (SHP1), cytokine-inducible (CIS) SH2-containing protein, suppressor of cytokine signaling-1 (SOCS1) and protein inhibitor of activated signal transducer and activator of transcription 3 (STAT3) (PIAS3) in six HTLV-1 negative and seven HTLV-1 positive T-cell leukemia lines.