TACI short isoform signaling promotes plasma-cell surface marker expression, plasma-cell transcriptional program, and plasma-cell morphology in human pre-B cells. (A) Representative flow cytometry dot-plots of CD19 and CD138 surface expression on resting NALM6, NALM6 GFP, and NALM6 TACI-expressing cells. Numbers indicate percentage of positive cells. (B) qRT-PCR of BCL6, PRDM1, PAX5, XBP1, and AICDA mRNAs from NALM6-transduced cells. Results are normalized to hypoxanthine-guanine phosphoribosyltransferase (HPRT1) mRNA and represented as relative expression. Data are from 5 independent experiments; error bars represent standard error of the mean. *P < .05; **P < .01 2-tailed unpaired Student t test. (C) Resting NALM6 and NALM6 TACI transfectants analyzed by transmission electron microscopy; >200 cells were assessed for each condition. Bar represents 2 μm; 5 μm for TACI short. E, euchromatin; H, heterochromatin; M, mitochondria; N, nucleus; RER, rough endoplasmic reticulum; V, vacuoles.