CIRCULATING MEGAKARYOCYTES AND THEIR PROGENITORS (BFU-MK AND CFU-MK) IN TERM AND PRETERM NEONATES

Thrombocytopenia is a common occurrence in sick newborn babies. Despit e this, platelet production in the newborn has rarely been assessed, p rincipally because of the difficulties of obtaining bone marrow, espec ially on a serial basis. We have developed two miniaturized assay syst ems to study megakaryocyte (MK) progenitor cell differentiation, from BFU-MK and CFU-MK to mature MK, by culturing mononuclear cells purifie d from 0.5-1 ml of neonatal peripheral blood. BFU-MK and CFU-MK were a ssayed in agar, whilst total cultured MK precursors and mature MK were assessed in liquid culture. In both systems, MK lineage cells were id entified morphologically and by an anti-IIb/IIIa antibody (CD61). Norm al ranges for MK precursors in term neonates were established from cor d blood studies of 40 healthy term babies and compared with cord blood studies in 16 non-thrombocytopenic pre-term babies (gestational age r ange 24-36 weeks). Pre-term babies had greater numbers of all MK precu rsors than term babies: BFU-MK 414 +/- 61 v 151 +/- 18 colonies/ml (me an +/- SEM); CFU-MK 2444 +/- 337 v 869 +/- 64 colonies/ml; total MK pr ecursors 213 +/- 36 v 54 +/- 6 x 10(3) cells/ml and mature MK 20 +/- 4 v 7 +/- 1 x 10(3) cells/ml. In addition, in newborn babies (n = 22), with no evidence of platelet consumption, circulating MK progenitor nu mbers at birth correlated with platelet numbers. These data indicate t hat in the newborn the measurement of circulating MK precursors provid es a good indicator of megakaryocytopoiesis, and hence platelet produc tion, and therefore is a useful and practical way of investigating neo natal thrombocytopenia.