Expression of TACI isoforms in primary human B cells. (A) Qualitative analysis of TACI cDNA expression in freshly isolated B cells from 2 healthy donors (HD1 and HD2). TACI sequences were amplified from mRNA by RT-PCR and examined by gel electrophoresis. Two bands correspond to each of the 2 isoforms. (B) TACI immunoblot from the same healthy donors expressing the 2 TACI protein bands. β-actin was used as loading control. (C) Quantitative analysis of CD27⁺, naïve IgD⁺, and total CD19⁺ B cells of TACI isoforms from freshly isolated peripheral blood mononuclear cells further cultured with or without ODN for 3 days. (D) Quantitative analysis of mRNA levels of TACI isoforms in freshly isolated B cells from spleens. Follicular (Fo) and marginal zone (MZ) B cells were cultured for 3 days with the addition of ODN or interleukin-21 (IL21) and CD40L. For panels C and D, data represent 3 different donors; error bars represent standard error of the mean. *P < .05; 2-tailed unpaired Student t test.