Studies of leukocyte kinetics by liquid scintillation counting in normal individuals and in patients with chronic myelocytic leukemia

Leukocyte kinetics have been investigated with the use of a number of different radioisotopic la-bels including 32p as disodium acid phosphate and as diisopropylfluorophosphate (DFP32), adenine-14C, and guanine (1-4). All of these have disad-vantages that limit their usefulness. The 32p_ labeled phosphate and the 14C compounds readily exchange with corresponding body pools and hence are not pulse labels. The quality of their emissions does not permit precise radioautography so that kinetics of specific cell types cannot be followed. The use of DFP32 is limited because it does not label the early precursor cells. However, Athens and associates (3, 5, 6) have obtained a great deal of valuable quantitative data using this label, par-ticularly in defining the intravascular leukocyte compartments and intravascular survival time. Since thymidine was first tritiated in 1955. it has become the most important tool for radioauto-graphic studies of leukocyte dynamics (7-9). It has achieved this importance because it is a spe-cific precursor for DNA and is exclusively and efficiently incorporated into DNA. After in-jection, the tritiated thymidine (3HTdR) that is not incorporated is quickly catabolized to sub-stances not utilizable for DNA synthesis and largely excreted. Negligible amounts of the label are found in the acid soluble pool or associated with RNA or protein when these are extracted by the usual techniques. This makes it an excel-lent tool for cytochemical studies (10). Since its beta emissions are of low energy, radioautographs with high resolution may be obtained. * Submitted for publication September 7, 1965; ac