Effect of a Nitric Oxide Donor on Intracellular Cytokine Production in Normal Human Peripheral Lymphocytes

It has been recently suggested that nitric oxide (NO) plays an important role in modulating immune responses including helper T (Th) cell differentiation. To investigate the effect of NO on cytokine production in T cells, we examined in vitro the percentage of interferon (IFN)-γ and interleukin (IL)-4 producing cells by the intracellular cytokine staining method with flow cytometry. The percentage of IFN-γ and IL-4 producing cells reached maximal value 8 h after stimulation by phorbol 12-myristate 13-acetate (PMA) and ionomycin. When an NO donor, sodium nitroprusside (SNP), was co-incubated with PMA and ionomycin for 8 h, nitrite levels increased in a dose dependent manner for SNP (P = 0.007; Friedman test). The percentage of IFN-γ producing cells was diminished in consequence of the increasing doses of SNP (P = 0.002; Friedman test). While the percentage of IL-4 producing cells tended to be diminished by SNP, this difference, however, was statistically not significant (P = 0.062; Friedman test). Therefore, we have suggested that NO might affect Th cell differentiation through inhibition of Th1-cytokine production and might cause a Th2 cell predominant state.