Monocytopoiesis in normal man: pool size, proliferation activity and DNA synthesis time of promonocytes.

Monocytopoiesis was analyzed in the bone marrow of healthy individuals. Promonocytes were identified by simultaneous determination of sodium-fluoride-sensitive and resistent naphthol-AS-D-acetate esterases. DNA synthesis activity of enzyme-positive promocytes was determined by 3H-thymidine (3H-TDR) incorporation in vitro. DNA synthesis time of these cells was measured by a double labelling technique (3H-TDR in vivo, 14C-TDR in vitro) as well as by serial injections of 3H-TDR. The relative number of promonocytes in the myelogram averaged 2.9% corresponding to a medullar promonocyte pool of about 600 X 10(6) cells per kilogram body weight. The promonocytes were classified into 4 groups on the basis of nucleus morphology: type I promonocytes with small lymphocyte-like nuclei (mean frequency of occurence, F = 5%; mean 3H-TDR labelling index, LI = 7.1%; type II promonocytes with large round or oval nuclei (F = 31%; LI = 9.7%); type III promonocytes with large, slightly folded nuclei (F = 51%; LI = 10.1%); type IV promonocytes with large, distinctly folded nuclei (F = 13%; LI = 24.9%). LI of pooled promonocytes was 12.0%. Mean DNA synthesis times of the different types of promonocytes was similar and approximated 10 h (range 6.6-13.3 h). This was true under normal conditions as well as in septicaemia.