Fig. 1

Single-cell-based development of anti-CoV-2-NP mAbs. a FACS gating strategy for the isolation of Wuhan CoV-2-NP-specific plasma cells. Plots (I)–(IV) represent the sequential gating strategy. (I) FSC vs. SSC with gate R1 represents lymphocytes. (II) Single cells were selected via DAPI staining (R2). (III) Cells labeled with CoV-NP were excluded from the R3 gate. (IV) The CoV-2-NP^High CoV-NP^Low and anti-guinea pig IgG^High fraction was defined as Wuhan CoV-2-NP-specific plasma cells (R4 gate). Percentages show the content of each cellular subpopulation among the total number of lymph node cells. b Representative agarose gel electrophoresis of the cognate pairs of immunoglobulin heavy chain variable (VH) and light chain kappa variable (VL) genes amplified from the single-cell-sorted R4-gated cells in (A). Line M: 1 kb DNA ladder (New England Biolab). Arrowheads indicate the size of the amplified DNA fragments. c The antigen specificity of the mAbs produced from the R4-gated cells. Cognate pairs of immunoglobulin heavy and light chain genes were cotransfected into HEK293 cells, and the CoV-2-NP binding activities of the expressed mAbs (5 ng) were analyzed by ELISA. The red line indicates the cutoff line for the screening