ETCs persist longer in secondary lymphoid organs of FCs as compared with MCs. Hematopoietic chimeras received late adoptive transfer (AT) with 40 × 10⁶ ETCs:R-DCs_pulsed (ETCs:R-DCp), ETCs:R-DCs_nonpulsed (ETC:R-DCnp), or naive DLI. The effectors were labeled with 5 μM CFSE. Spleens of the transplanted animals were harvested 3 or 7 days later, single cell suspensions were made and analyzed for CFSE intensity. (A) Representative day 7 results from flow cytometric analysis of harvested splenocytes from MCs and FCs are shown. A CFSE high peak (nondivided ETCs) was detected in FCs only (the marker labels the CFSE high/low region). (B) Adoptively transferred ETCs clear faster from MCs than from FCs. Spleens from MCs and FCs were harvested on days 3 and 7 after delayed adoptive transfer. Data obtained from animals that received either ETCs:R-DCsp or ETC:R-DCsnp are presented separately. A DLI group was added as a control. The fraction of CFSE^hi cells (indicating nondivided ETCs) and CFSE^lo cells (indicating proliferated ETCs) was determined by flow cytomertic analysis. (C) Both, in MCs and FCs more vigorous proliferation of ETCs is seen when adoptive transfer is performed early after transplantation (day 21). Spleens from MCs and FCs were harvested on day 7 after early or delayed AT. The absolute number of CFSE^hi and CFSE^lo cells was calculated. Mean values are presented plus or minus SE.