REGULATION OF MEGAKARYOCYTE COLONY-FORMING CELL NUMBERS AND PLOIDY BYDIDEOXYNUCLEOSIDES IN IMMUNODEFICIENT MICE

We have recently demonstrated that azidothymidine (AZT) elevates the l evels of circulating platelets in mice made immune deficient by infect ion with LP-BM5 murine leukemia virus (MAIDS mice). In an attempt to e lucidate the mechanisms of the AZT platelet elevating effect, we exami ned the number of splenic and bone marrow megakaryocyte colony-forming cells (CFU-mk) and the ploidy of megakaryocytes derived from CFU-mk u sing fluorescence cytophotometric methods. Two other dideoxynucleoside s (ddN) 2'3'-dideoxyinosine (ddl) and 2'3'-dideoxycytidine (ddC) were assessed to determine the specificity of the effect of AZT. MAIDS mice were given ddN in drinking water for 15 days. AZT was the only ddN th at significantly increased circulating platelet levels in MAIDS mice. AZT significantly increased splenic CFU-mk in MAIDS mice, but bone mar row CFU-mk were not affected. ddl and ddC failed to change either plat elet levels or the numbers of splenic or bone marrow CFU-mk. The ploid y of megakaryocytes derived from splenic and bone marrow CFU-mk were e xamined by first identifying CFU-mk by staining for acetylcholinestera se, followed by nuclear staining with propidium iodide. The fluorescen ce of individual cells was then measured using a Perceptics image anal ysis system. Modal ploidy of CFU-mk megakaryocytes derived from spleen cells of AZT-treated immunodeficient mice was shifted upwards from 16 N to 32N. Similarly, AZT treatment changed the modal ploidy number of colony megakaryocytes derived from bone marrows of immunodeficient mic e from 16N to 32N. The ploidy distribution was also significantly shif ted. ddl and ddC failed to significantly alter either modal ploidy num ber or distribution of megakaryocytes derived from splenic or bone mar row CFU-mk. These findings suggest that AZT may effect physiological p rocesses that lead to platelet formation. (C) 1993 Wiley-Liss, Inc.