Search

A suspension of fine carbon particles was added to cord blood of healthy premature and full-term infants, and the mixture was incubated for 3 h, after which the uptake of carbon particles by blood leukocytes was examined. The results were compared with those from the blood of adults. A gradient of phagocytic activity was observed. The most active uptake of carbon was by the leukocytes of premature infants, the least active by leukocytes of adults. In cord blood and blood of adults, phagocytic activity was evident in both monocytes and neutrophils. In addition, two types of what have been termed 'lymphocytoid' phagocytes were seen. These resemble lymphocytes in their morphology. One type possesses basophilic cytoplasm, and has been found only in premature cord blood. The presence of lymphocytoid phagocytes affords a further indication of the differences between the circulating lymphocyte population in the prenatal and perinatal period as compared with the adult.

Cord blood cells from 8 full-term and 12 premature infants as well as blood leukocytes from 10 adults were incubated with 3H-thymidine and were subsequently exposed to autoradiographic emulsion for prolonged periods of 45 and 90 days. Cytoplasmic label -- which were interpreted as evidence of mitochondrial DNA synthesis -- was found in 1.7 per cent of lymphoid cells from adult blood, in 2.9 per cent and 4.5 per cent of lymphoid cells from full-term and premature infants, respectively. Statistical analysis of the data shows that the number of labelled cells is significantly larger in the blood of premature infants than in adults (p less than 0.01).

CFU-F (colony forming units-fibroblast) were studied from cord blood and, as controls, from normal bone marrow of older children and adults. Numbers of CFU-F in cord blood buffy coat cells are lower by a factor of 10 in comparison to bone marrow CFU-F. Cytomorphology and staining with monoclonal antibody identify the progeny cells of CFU-F as fibroblasts. Cord blood CFU-F derived fibroblasts have properties supporting hematopoiesis: They produce CSF (colony stimulating factor) to which fresh cord blood CFU-GM (colony forming units-granulocytic, monocytic) react by colony formation in a dose-response manner. In addition, fibroblast colonies discharge clonogenic round cells into the medium forming CFU-GM and CFU-F colonies in secondary methyl cellulose cultures. We conclude that fetal blood contains clonogenic stromal cells (CFU-F) that give rise to fibroblasts with properties of hematopoietic support.

Colony forming units (CFUc) giving rise to myelocytic colonies in methylcellulose cultures were found among non-adherent mononuclear cells of human cord blood with a frequency of one in 1678. The number decreased makredly during the first 8 to 10 days of life. They were rarely detected in adult blood by this technique.

The potential of hematopoietic stem cells from cord blood for proliferation and differentiation have been studied by the diffusion chamber technique. In a pilot study, it was shown that blast cell production and myelopoiesis from the original lymphoid cell suspension starts 6 days after implantation. Mature granulocytes and megakaryocytes respectively appear in the chambers from the 16th and 10th days onwards. Myelopoiesis is ten times more active in fetal than in adult blood. There were thrombopoietic stem cells in 7 of 10 cord blood samples but in only one of 10 adult blood specimens. It is concluded that the high hematopoietic activity of the bone marrow at term is reflected by an increase in the number of stem cells circulating in the blood. Myelo- and thrombopoietic stem cells must be sought among the lymphoid cells of the original cord blood cell suspension.

The radiosensitivity of human cord blood haematopoietic stem cells was measured by assessing colony formation in methylcellulose cultures and diffusion chambers. The results show that fetal colony forming units, granulocytic, monocytic (CFU-GM), are radiosensitive: colonies formed by electron-irradiated CFU-GM, both in spontaneous and in colony stimulating factor (CSF) supplemented cultures decrease in number in an exponential fashion with increasing doses of irradiation. Do values up to 800 rads were, for highly purified fetal lymphoid cells, 160 +/- 88 rads; for whole buffy coat cells, 155 +/- 75 rads; and for buffy coat cells plus exogenous CSF: 155 +/- 77 rads. Extrapolation numbers (N) approached the value of 1. Among cord blood diffusion chambers progenitor cells (DCPC), radiosensitive and radioresistant subpopulations of myelopoietic stem cells exist, as tested over a range up to 1500 rads. Monocytopoietic CFU-D are radioresistant.