Pik3cd GOF antibody-secreting plasmablasts express unmutated antibody variable region genes. Individual Pik3cd^GOF self-reactive plasmablasts (n = 25) and GC (n = 88) cells were sorted from nine different mice in six different experiments, and then the antibody heavy chain variable region of each cell was sequenced. (A) Graphs show the number of nucleotide mutations per cell, the center line shows the median, box limits show the upper and lower quartiles, and whiskers show the minimum and maximum. The dashed line shows the mean background rate of mutations detected in non-GC SW_HEL B cells. (B) Percentage of mutated GC sequences with the canonical affinity-increasing mutation at tyrosine (Y) 53 (Y53D) and the known affinity-decreasing mutations at position serine (S) 52 (S52N and S52R). (C and D) Cells were stained to identify the level of HEL binding by surface BCR. (C) Histograms show representative staining. (D) Graphs show the percentage of SW_HEL plasmablasts and GC cells that retained the ability to bind HEL (the center line shows the median, box limits show the upper and lower quartiles, and whiskers show the minimum and maximum (n = 15–19 mice combined from seven experiments). Significant differences were determined using Mann-Whitney test. ****, P < 0.0001.