(A) Study design. Peripheral blood from six donors was sampled at three time points: T1 – initial time point, T2 – 1 month, and T3 – 12 months after the start of the study. At each time point, we isolated peripheral blood mononuclear cells (PBMCs) and sorted memory B cells (Bmem: CD19+ CD20+ CD27+), plasmablasts (PBL: CD19low/+ CD20- CD27high CD138-), and plasma cells (PL: CD19low/+ CD20- CD27high CD138+) in two replicates using fluorescence-activated cell sorting (FACS). For each cell sample, we obtained IGH clonal repertoires by sequencing respective cDNA libraries covering full-length IGH variable domain. (B) Proportion of isotypes in studied cell subsets averaged across all obtained repertoires. Left, frequency of unique IGH clonotypes with each particular isotype. Right, frequency of each isotype based on IGH cDNA molecules detected in a sample. (C) Distribution of the number of somatic hypermutations identified per 100 bp length of IGHV segment for clonotypes within each particular isotype. (D) Distribution of CDR3 length of clonotypes in each cell subset by isotype. (E) Distributions of average IGHV gene frequencies based on number of clonotypes in naive B cells (data from Gidoni et al., 2019), Bmem, PBL, and PL repertoires are shown at the top. Colored squares on heatmap indicate significantly different (false discovery rate, FDR < 0.01) frequencies for IGHV gene segments in corresponding B cell subsets compared to naive B cell repertoires. Color intensity reflects the magnitude of the difference (FC = fold change). Only V genes represented by more than two clonotypes on average are shown, data normalization was performed using trimmed mean of M values method (Robinson and Oshlack, 2010). IGHV gene segments are clustered based on the similarity of their amino acid sequence, as indicated by the dendrogram at the bottom. In C and D, the numbers at the bottom of the plots represent the number of clonotypes in the corresponding group, pooled from all donors, and the median measurements from each cell type. Comparisons between subsets were performed with two-sided Mann-Whitney U test. *=p ≤ 0.05, **=p ≤ 0.01, ***=p ≤ 10–3, ****=p ≤ 10–4.