Eyer, K. et al. Nat. Biotechnol. http://dx.doi.org/10.1038/nbt.3964 (2017).

B lymphocytes are a key component of the immune arsenal; upon antigen challenge, these cells undergo affinity maturation in lymphatic organs and differentiate to become antibody-secreting cells. Next-generation sequencing can profile expressed IgG variants across many individual secreting cells, but methods to measure the functional properties of these antibodies remain laborious and low in throughput. Eyer et al. present a microfluidic platform called DropMap that traps tens of thousands of picoliter-sized droplets containing individual antibody-secreting cells in a two-dimensional array. An in-droplet sandwich immunoassay uses functionalized paramagnetic nanoparticles to capture and quantify secreted IgG, which makes it possible to measure secretion rate as well as antibody specificity and affinity from the same cell. The authors use DropMap to profile thousands of antibody-secreting cells from mouse spleen and bone marrow in response to tetanus toxoid immunization.