Human Monocytes and Lymphocytes Differ in the Rate of DNA Repair Synthesis and Viability after Exposure to Nitrogen Mustard

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Abstract
Unscheduled DNA synthesis was studied in human lymphocytes and monocytes after treatment with nitrogen mustard, methyl methanesulfonate and UV irradiation. The unscheduled DNA synthesis was about 4 times higher in monocytes than in lymphocytes after treatment with nitrogen mustard. Treatment with methyl methanesulfonate or UV irradiation confirmed the higher capacity for unscheduled DNA synthesis in the monocytes. When Ficoll-Isopaque-isolated mononuclear cells were exposed to various doses of nitrogen mustard and incubated for different periods, a dose- and time-dependent increase in trypan blue uptake was found. A corresponding dose- and time-dependent decrease was noted in 3H-uridine incorporation. Since trypan blue uptake will not enable differentiation between monocytes and lymphocytes appearing as a mixed cell population, 3H-uridine flash labeling index was studied after exposure to nitrogen mustard. There was a dose- and time-dependent decrease in 3H-uridine labeling index, suggesting a correlation between the absence of 3H-uridine incorporation and increase in trypan blue uptake. When compared to monocytes, the lymphocytes were more affected in this respect after exposure to nitrogen mustard. The possibility that differences in cytotoxic effect may be related to DNA repair mechanisms is discussed.

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