Stimulation: Biotin-anti-CD3 (553060), Biotin-anti-CD4 (553728), and Biotin-anti-CD28 (553296) were from BD Biosciences. Immunoprecipitation: anti-Flag (F1804) Sigma Aldrich; anti-SHP-1 (SC287), anti-SHP-2 (SC280) Santa Cruz. Western blotting: anti-pTyr (05321), anti-GST (06332), anti-ERK (06182), anti-SHP-1 (06117) EMD Millipore; anti-pTyr564-SHP-1 (8849), anti-pTyr416-Src (2101) Cell signaling Technology; anti-pTyr319-ZAP-70 (612574), anti-GRB2 (610111) BD Biosciences; anti-LCK (SC433), anti-ZAP-70 (SC574), anti-pERK (SC7383), anti-HA tag (SC805) Santa Cruz; anti-PTPN7 (ab118978) Abcam; anti-Myc tag (M0473) MBL International; anti-SHP-1 (MS1190) Thermo Fisher; anti-pTyr536-SHP-1(SP1571) ECM Biosciences; anti-actin (A5441) Sigma Aldrich; anti-pPLC-γ1 (44-696G) Biosource;, anti-Oxidized PTP active site mAb (MAB2844) R&D Systems. Rabbit polyclonal antisera to THEMIS7 (link) and THEMIS213 (link) have been described. Streptavidin-HRP conjugate was purchased from Sigma Aldrich. Streptavidin was purchased from Southern Biotechnology.