[In vitro growth characteristics of rIL3 stimulated megakaryocytic progenitor cells (CFU-MK) of fetal liver].

In this study, plasma clot and methycellulose semi-solid and liquid culture technigues were employed to observe the in vitro growth characteristics of proliferation and differetiation of 4-5 months fetal liver and adult bone marrow CFU-MKs. Fetal liver MK colonies in plasma clot in the presence of rIL3 or Meg-CSA were larger (usually with > 50 cells/colony) than that of the adult (usually with < 50 cells/colony). The number (36.40 +/- 16.60/1 x 10(5) cells) of fetal liver Mk colonies in presence of 2 ng/ml rIL3 was larger than that (10.05 +/- 2.81/1 x 10(5) cells) of human adult bone marrow MK colonies (P < 0.01). In contrast, the major DNA ploidy classes of megakaryocytes derived from fetal liver CFU-MK were those of 2N and 4N cells and the major DNA ploidy classes of megakaryocytes derived from human adult bone marrow were those of 8N and 4N cells. The mean (5.45 +/- 0.86) of the ploidy of the former was lower than that (10.13 +/- 1.30) of the latter (P < 0.01). The same results were obtained with the presence of 10% Meg-CSA. These present results indicated that CFU-MK in fetal liver has a high ability of proliferation and low capacity of differentiation (polyploidization). Interestingly, the number of fetal liver MK colonies increased in the range of rIL3 concentration from 0.5 ng/ml to 2 ng/ml. At higher rIL3 concentration (2-8 ng/ml), the colony growth showed a steady decrease from the maximum value instead of an increase. However, in the same range of rIL3 concentration, the numbers of adult bone marrow MK colonies numbers and fetal liver CFU-GM colonies increased steadily and finally reached to a plateau. Furthermore, both fetal liver and adult bone marrow MK colonies showed dose-dependent response in the range of Meg-CSA concentration from 5% to 25%. In addition, there was no difference on DNA ploidy distributions of megakaryocytes derived from fetal liver CFU-MK between rIL3 and Meg-CSA as growth factors. Moreover, the DNA ploidy distribution of fetal liver derived megakaryocytes stimulited by rIL3 could not be changed by addition of rIL6 (100 u/ml). In summary, the above data suggest that CFU-MK in the fetal liver undergoes some intrinsic cellular modification in order to suit the need of ontogensis.