FIGURE 1.

Characterization of anti–human class II MHC VHH (VHH4). (A) Schematic representation of sortase reaction to site-specifically labeled VHHs followed by liquid chromatography–mass spectrometry analysis. Sortase recognizes LPXTG motif and replaces G residue with substrate containing a NH₂-G₃-R moiety, where R represents tag of interest. Liquid chromatography–mass spectrometry analysis on VHH4 and VHH4-Texas Red confirms efficient labeling for VHH4. (B) Sodium dodecyl sulfate polyacrylamide gel electrophoresis characterization of VHH4: lane 1, marker; lane 2, VHH4; lane 3, VHH4-Texas Red (left); and same sodium dodecyl sulfate polyacrylamide gel electrophoresis gel scanned for Texas Red fluorophore (right). (C) Freshly isolated human peripheral blood lymphocytes cells were stained with VHH4-Texas Red and B and T cell lineage-specific antibodies. Representative data of 1 of 3 donors.