Figure 3. Integration of bulk and single-cell transcriptomic data identifies cross-tissue infiltration of Igj^high plasma B cells.

a, Aco1 and Ms4a7 kidney mRNA expression. LOESS regression indicated by black line. Spearman’s rank correlation coefficient ρ is indicated. Means ± SEM. b, A gene with ‘disperse’ (Aco1) and ‘specific’ (Ms4a7) single-cell expression pattern in kidney. n=1,108 cells. c, Single-cell dispersion scores (scRNA-seq) with Spearman’s rank correlation coefficient (≥ 0.6; bulk RNA-seq) for a given tissue. Color represents organ type. Dot size corresponds to % of cells per tissue expressing a given gene. d, t-SNE visualization of scRNA-seq data (FACS) from GAT, colored by age. A cluster of B cells present only in aged GAT is circled. e, GAT B and T cells as a percentage of all analyzed cells. n=4 independent animals. T-test, means ± SEM. f, Expression of B cell marker Cd79a and plasma B cell marker Igj. g, t-SNE visualization of scRNA-seq data (droplet) of all Cd79a-expressing cells present in the Tabula Muris Senis dataset (17 tissues), colored by the plasma B cell markers Igj and Xbp1. h, GO terms enriched among the top 300 marker genes of Igj^high (n=1,198 cells) versus B cells (n=22,598 cells), with 1,886 genes passing filtering as background. q-values estimated with Benjamini-Hochberg for each database separately, and for GO classes (molecular function, cellular component, biological process) independently. i, Distribution of IgJ^high as percentages of Cd79a expressing cells per tissue. j, Representative FACS scatterplots from 2 independent experiments showing increased plasma cell abundance in aged bone marrow. Cd138, plasma cell marker. B220, B cell marker. k, FACS quantification for kidney and marrow. n=4 independent animals. T-test, means ± SEM l, Representative images from 2 independent experiments of Igj RNAscope of 3mo and 24mo kidney. Virtually no Igj signal was present in young kidneys. 100μm scale bar.