Abstract
IgD is the least well characterized of mammalian antibody isotypes and its biology remains poorly understood. Nanobodies are a useful and versatile tool for research and diagnostics, including for protein purification, capture and detection applications. Here we report the characterization of four anti-human IgD nanobodies, specific to the Fc region of IgD. The four nanobodies bound to human IgD with low nanomolar affinity, showing different binding kinetics and interaction stoichiometries, as well as recognizing four distinct epitopes. We found one of these anti-IgD nanobodies, aδNb408, to be an excellent purification tool for IgD, with efficient capture and elution at pH 3.5. To aid the analysis of IgD interactions using surface plasmon resonance, we identified two nanobodies that provided good capture of IgD. Assembling bispecific and bivalent nanobody pairs increased the avidity of the anti-IgD nanobodies, with the bispecific nanobody pair aδNb408-aδNb107 showing robust detection of IgD on Namalwa B cells. The anti-IgD nanobody tools described here can be used for diverse applications that have the potential to further our understanding of IgD biology.