Differential NF-κB activation by TACI isoforms in human pre-B cells. (A) Confocal microscopy of isolated nuclei from NALM6 nontransduced cells, NALM6 GFP, NALM6 with TACI short or long isoforms, and nonsignaling TACI S194X mutant cells, cultured as in Figure 4 and stained for p65 (red); nuclei were counterstained with DAPI (blue). Images show white dividing lines for cells taken from the same field. Original magnification ×63. (B) Quantitative assessment of p65 nuclear translocation (relative to cell number), represented as p65 relative intensity. The mean percentage and standard error were calculated from 3 independent experiments; error bars represent standard error of the mean. *P < .05; **P < .01; 2-tailed unpaired Student t test. (C) Immunoblot analysis of p65 nuclear translocation after subcellular fractionation of resting cells after 6-hour starvation. (C: cytoplasmic fraction; N: nuclear fraction; GAPDH: cytoplasmic fraction loading and purification control; and Nucleoporin/p62: nuclear fraction loading and purification control). For quantitation of nuclear p65 levels, >200 cells were microscopically assessed and analyzed with ImageJ software.