NAD metabolism and mitogen stimulation of human lymphocytes

The NAD concentration in eukaryotic cells is an important parameter for many aspects of metabolism including differentiation. As reported by other workers, the NAD content of resting human peripheral blood lymphocytes was low and increased dramatically over a period of 3 days after stimulation with the mitogen phytohemagglutinin (PHA). However, simultaneous measurement of the mean cell volumes showed that the average NAD concentration in fresh quiescent lymphocytes (401 +/- 128 microM) (SD, n = 7) was similar to that observed for other cell types. Furthermore, because of the increase in cell volume which occurred on mitogen stimulation, the NAD concentration in stimulated lymphocytes was only 2-3-fold higher than in fresh resting cells. This increase was also observed in lymphocytes incubated without mitogen and was apparently due to the level of NAD precursors in the culture medium and serum supplement. Hence, the NAD concentration in resting and stimulated lymphocytes is comparable to that of other eukaryotic cells and the variations in NAD content reported earlier have been widely misinterpreted.