Apoptosis of MRL/lpr and BALB/cJ spleen lymphocytes with exogenous nitric oxide in vitro. MRL/lpr and BALB/cJ spleen lymphocytes were isolated and cultured overnight in varying concentrations of Deta NONOate. Cells were harvested and analyzed for apoptosis using annexin V—fluorescein isothiocyanate staining and flow cytometry. A, The results were normalized to the percentage of apoptotic cells relative to control wells (not exposed to Deta NONOate) and reported as the average ± standard error of five experiments for MRL/lpr mice and two experiments for BALB/cJ mice MRL/lpr spleen lymphocyte apoptosis was represented with closed circles, whereas BALB/cJ apoptosis was represented with open circles. The results were reported as a percentage of control conditions (no added Deta NONOate). For MRL/lpr spleen lymphocytes, p < .001 for treatment effect. For BALB/cJ spleen lymphocytes, treatment effect was not statistically significant across two experiments. B, Representative single experiment from data reported in A The results were reported as the percentage of intact cells that were apoptotic.