The following mAbs against the human molecules CD3 (SK7), CD19 (SJ25C1), IgG (G18-145) (BD-Pharmingen, San Diego, CA), CD27 (O323; eBioscience) and IgA (F(ab) 2 , DAKO), were directly labeled with either fluoroscein isothiocyanate (FITC), phycoerythrin (PE), phycoerythrin cyanine 5, (PE-Cy5), allophycocyanin (APC), phycoerythrin-indotricarbocyanine (PE-Cy7), phycoerythrin-cyanine 7 (PC7) or allophycocyanin-indotricarbocyanine (APC-Cy7). Recombinant TT C-fragment was purchased from Boehringer Mannheim (Mannhein, Germany) and conjugated to PE (Cyanotech Corporation, Kaila-kona, HI) as previously described [27] . Stained cells were sorted using a FACSAria (BD) and analyzed using a LSR-II (BD) and flow cytometry data were processed with FlowJo computer software (Treestar, Ashland, OR).