Characterization of Asia 1 sdAb from Camels Bactrianus (C. bactrianus) and Conjugation with Quantum Dots for Imaging FMDV in BHK-21 Cells

Foot-and-mouth disease (FMD), caused by FMD virus (FMDV), is a highly contagious viral disease affecting cloven-hoofed animals. Camelids have a unique immunoglobulin profile, with the smallest functional heavy-chain antibodies (sdAb or VHH) naturally devoid of light chains with antigen-binding capacity. We screened and characterized five sdAbs against FMDV by immunized library from C. bactrianus with Asia 1 virus-like particles (VLPs). Three of five recombinant sdAbs were stably expressed in E.coli, remained highly soluble, and were serotype-specific for VP1 protein of FMDV Asia 1 by ELISA. These failed to completely neutralize the Asia 1 virus. According to the KD value of binding affinity to three sdAbs, which ranged from 0.44 to 0.71 nm by SPR, sdAb-C6 was selected and conjugated with Zn/CdSe quantum dots (QDs) to form a QDs-C6 probe, which was used to trace and image the subcellular location of FMDV in BHK-21 cells. The results show that FMD virions were observed from 3 h.p.i., and most of virions were distributed on one side of the nucleus in the cytoplasm. We demonstrate the utility of sdAbs as functionalized QDs are powerful tools for FMDV research.