Nitric oxide promotes growth and major histocompatibility complex-unrestricted cytotoxicity of...

The effect of nitric oxide (NO) on growth and major histocompatibility complex(MHC)-unrestricted cytotoxicity of interleukin(IL)-2-cultivated rat spleen nonadherent mononuclear cells was examined. NO donor sodium nitroprusside (SNP) at relatively low concentrations increased magnitude, as well as duration of IL-2-induced proliferative response of nonadherent splenocytes. SNP effect depended completely on released NO, because it was prevented by NO scavenger haemoglobin, but not mimicked by expired SNP solution, unable to generate NO, or ferricyanide, a second breakdown product of SNP. Other NO donors - SIN-1, SNAP and GSNO failed to exert SNP-like growth-enhancing action, probably as a consequence of rapid NO generation, compared to sustained NO release by SNP. All NO-releasing chemicals at high concentration blocked IL-2-induced proliferation. Growth-promoting effect of SNP-derived NO was independent of guanilat cyclase activation, because dibutyryl cGMP did not affect IL-2-triggered splenocyte proliferation. Macrophage NO acted in a manner similar to SNP; at low concentrations it promoted IL-2-induced splenocyte growth, however higher amounts were suppressive. Cytotoxicity of IL-2-activated splenocytes against NK-sensitive K562 cell line was significantly increased when SNP was present during cultivation with IL-2. Proportion of NKR-P1+ and CD25+ cells, as well as per cell expression of these important activation molecules were increased upon SNP treatment, suggesting possible mechanism for the observed NO action.