MTA3 is coexpressed with BCL6 exclusively within GC B cells. (A-C) Immunohistochemistry in lymphoid follicle with GC from human tonsil. A CD20 (brown) and MTA3 (blue). (B) Dual immunofluorescence in which MTA3 is labeled in red and BCL6 in green. Cells expressing both proteins display a yellow signal. The circles denote cells used as a reference in the lower 2 panels to demonstrate lack of bleed-through between the fluorescence channels. (C) MTA3 (blue in all 3 panels) along with either CD138 (plasma cell marker), CD3 (T-cell marker), and CD68 (histiocyte marker) respectively, all in brown. (D-F) Purified human tonsillar NBCs and CBs were assessed by (D) real-time PCR for BCL6 and MTA3 mRNA (where the y-axis depicts mRNA abundance normalized to the level found in NBCs). Error bars are SD. (E) Immunoblots with antibodies for MTA3, BCL6, and actin as loading control. (F) Expression microarray analysis visually represented here by a heat map of mRNA levels in NBCs, CCs, CBs, and memory B cells. The scale shows relative mRNA abundance (red = higher, blue = lower).