Isolation and characterization of plasmablasts

Fresh peripheral blood mononuclear cells were stained with fluorescent-labelled antibodies including Pacific blue anti-CD3 (clone UCHT1, catalogue number 558117, BD) (5 μg/ml), fluorescein isothiocyanate anti-CD19 (clone HIB19, catalogue number 555412, BD) (1:10 dilution in a 100 μl experimental sample), phycoerythrin-Cy7 anti-CD27 (clone M-T271, catalogue number 560609, BD) (1:20 dilution in a 100 μl experimental sample), allophycocyanin-H7 anti-CD20 (clone L27, catalogue number 641396, BD) (5 μg/ml) and phycoerythrin-Cy5 anti- CD38 (clone HIT2, catalogue number 555461, BD) (1:10 dilution in a 100 μl experimental sample). CD3^negCD20^negCD19^posCD27^hiCD38^hi plasmablasts were gated (Supplementary Fig. 14a) and sorted as single cells. Heavy and light chain variable domains of single plasmablasts were cloned into their respective vectors and supernatants were collected from 293T cells co-transfected with the heavy chain and light chain vectors designed to express human IgG1^{13 (link)}.