Nonmalignant GC B-cell precursors of HRS cells express TACI, BCMA, and BAFF-R. (A-E) IgD (green), TACI, BCMA, BAFF-R, BAFF, and APRIL (red) in tonsillar tissue sections. In panel C, yellow indicates follicular mantle B cells coexpressing IgD and BAFF-R. Original magnification ×10. (F) IgD and CD38 on purified tonsillar B cells. N indicates naive B cells; FGC, founder GC B cells; GC, GC B cells; M, memory B cells; and PC, plasmacytoid B cells. (G) TACI, BCMA, BAFF-R, CD30, CD40, and CD19 on purified tonsillar B cells gated into naive, FGC, GC, memory, and plasmacytoid subsets, and on EBV-transformed lymphoblastoid (LB) B cells. Open and shaded profiles correspond to antibody under study and control antibody, respectively. Panels A-G depict 1 of 4 experiments yielding similar results.