Figure 3.

Comparison of DNA synthesis in cord blood (CB) B cells and different fractions of tonsillar B cells (CD5-positive [CD5^pos] and CD5-negative [CD5^neg]) after the engagement of B-cell receptors (BCR) and/or CD40. B cells (10⁵ cells/well) were cultured for 3 days with: (i) non-transfected mouse L cells, (ii) CD32-transfected mouse L cells and anti-immunoglobulin M (IgM) antibody at 0·5 µg/ml (BCR), (iii) CD40 ligand (CD40L)/CD32-transfected cells (CD40) and (iv) CD40L/CD32-transfected L cells and anti-IgM antibody. [³H]Thymidine ([³H]Tdr) incorporation (in counts per minute [c.p.m.])was measured during the last 18 hr of culture. Values for [³H]Tdr uptake by mouse L cells alone were always less than 1000 counts per minute (c.p.m.) (results not shown). Data are given as the mean + SD of three experiments.