CD40 levels are similar on freshly isolated B cells from normal and Tg animals. Freshly isolated SPC from young and aged C57 (A and B) and QM (C-G) mice, were stained with anti-CD40 mAb along with anti-B220 and NP-PE. Percentages of B220+ lymphocytes are shown in (A) and (C), and CD40 expression (B and D) was determined for the B220+ population. Percentages of NP-specific QM B cells and non-NP binding cells are shown in E. The levels of CD40 on NP- and NP+/B220+ cells are shown in (F) and (G). Thin lines indicate cells from young animals and thick lines indicate cells from aged animals. Representative of 3 separate experiments.