Rescue of immature but not mature self-reactive B cells from sHEL/anti-HEL double Tg donors. FACS analysis of B220+ spleen cells obtained from sHEL Tg recipients of mature (a–f) or immature (g–l) B cells at 1 (a, b, g, h), 3 (c, d, i, j) and 5 (e, f, k, l) days after transfer. The majority of recipient CFSE− cells were excluded from collection to increase the sensitivity of detection of CFSE+ donor-derived cells. Undivided (dotted rectangles) and divided (rectangles with heavy borders) HEL-binding B cells are indicated. In addition, the proportion of surviving undivided donor-derived B cells that have down-regulated HEL-binding (rectangles with fine borders) is increased by T cell help, a phenomenon that is also apparent in vitro (not shown).