Open-CD3 outlasts TCR engagement by APCs. A, OT-I Rag−/− β2m−/− preselection DP thymocytes were cocultured for 30 min at 37°C with T2-Kb APCs that had been preloaded with either pFARL (null peptide), pOVA (antigenic peptide), or no peptide plus soluble anti-CD3ε mAb 2C11. Then, cocultures were lysed and subjected to the CD3-PD assay. CD3-PD samples were visualized for their content of 2C11, MHC-I H chain, and CD3ζ by WB. Open-CD3 inductions achieved by antigenic and 2C11 stimulation were calculated relative to the amounts of open-CD3 found in basal conditions (pFARL). B, T1 hybridoma cells were cocultured for 30 min with P-815 APCs that had been preloaded with either no peptide (Ø), pSYIP (antigenic peptide), or no peptide plus soluble anti-CD3ε mAb 2C11. Then, cocultures were lysed and subjected to the CD3-PD assay or H2-Kd immunoprecipitation with the mAb SF1-1.1. CD3-PD samples were visualized for their content of 2C11, MHC-I H chain, and CD3ζ by WB. Open-CD3 inductions achieved by antigenic and 2C11 stimulation were calculated relative to the amounts of open-CD3 found in basal conditions (Ø).