THE RESPONSE OF CORD-BLOOD MEGAKARYOCYTE PROGENITORS TO IL-3, IL-6 AND APLASTIC CANINE SERUM VARIES WITH GESTATIONAL-AGE

Fetal cord blood (CB) is rich in haemopoietic stem cells and progenito rs. We studied the clonogenic, proliferative and maturational response s of megakaryocyte (MK) progenitors in CB, from different gestational ages, to various cytokines: IL-3, IL-6, IL-3 + IL-6, and aplastic cani ne serum (PICS-J), and compared their responses to those of progenitor s in adult peripheral blood (PB) or bone marrow (BM). We found that 34 -week gestation CB produced some spontaneous colonies 28 +/- 4.7 CFU-M K in the absence of exogenous cytokines, and produced more CFU-MK and BFU-MK in response to IL-3, IL-6 and IL-3 + IL-6 than the other sample s tested. Proliferation of CFU-MK was maximal at 34 weeks and decrease d gradually toward term. When compared to adult BM or PB, the CB-deriv ed CFU-MK had increased cellularity and contained significantly more c ells undergoing fragmentation into platelet-like particles after stimu lation with IL-3 or IL-6. Post-irradiation aplastic canine serum (PICS -J) was a highly potent stimulator of MK progenitors at all developmen tal stages. Our results indicate that CB MK progenitors are exquisitel y sensitive to exogenous cytokines and that the magnitude of their pro liferative and maturational responses to cytokines is related to devel opmental age.