TACI expression in monocytes. (A) Surface staining of TACI, BCMA, and BAFF-R on freshly isolated monocytes. Specific receptor expression is indicated by the gray shaded curves, and isotype control staining is indicated by the open curves. (B) Intracellular staining of TACI, BCMA, and BAFF-R in freshly isolated monocytes. Fluorescence levels (FL) for each antibody are shown on the ordinate and forward light scatter (FSC) is shown on the abscissa. (C) Expression of TACI by Western blot analysis in freshly isolated CD14⁺ monocytes, B cells (B; positive control), or eosinophils (Eos; negative control). β-Actin was used as a loading control. (D) Cells were cultured with or without 200 ng/mL _LBLyS overnight, and then analyzed for surface expression of TACI, BCMA, or BAFF-R on viable cells as determined by FSC versus SSC. Isotype controls and fluorescence controls were performed for each sample (open curves).