Most CD38^highCD27⁺ASCs in human tissues express CD19. (A) Contour plots revealed a rare cell subset with high expression of CD38 and positive for CD27, which showed a clear cytoplasmic IgG, IgM, or IgA positive expression and was found in all human tissues (BM, PB, tonsil, and spleen) indicative of ASCs. (B) ASC (CD38^highCD27⁺) frequencies in human tissues: mean, %, and standard deviation (SD). (C) CD19⁺ ASCs were statistically more abundant that CD19⁻ ASCs in the BM (upper graph, unpaired Student t test, ****P < .0001, mean ± standard error of the mean (SEM) 23.14 ± 2.477 and 60.74 ± 3.994, both n = 16, median ± SD age 32 ± 7.713) and spleen (lower graph, unpaired Student t test, ****P < .0001, mean ± SEM 17.70 ± 2.983 and 64.7 ± 2.983, both n = 8, median ± SD age 51 ± 14.125). (D) CD38^highCD27⁺ ASCs or CD19⁺CD20⁺ non-ASC B cells from BM were sorted directly onto total IgG/IgM/IgA precoated ELISpot plates. BCs, B cells; Freq., frequency.