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This study explored the effects of reactive nitrogen metabolites (RNMS) on natural-killer- (NK-) cell-mediated killing of K562 cells and the influence of RNM scavengers, such as tiopronin (TIP), glutamylcysteinylglycine (GSH), and histamine dihydrochloride (DHT), on reversing the suppressing effect of RNM. We administered exogenous and endogenous RNM in the NK + K562 culture system and then added RNM scavengers. The concentrations of RNM, TNF- β and IFN- γ , and NK-cell cytotoxicity (NCC) and the percentage of living NK cells were then examined. We found that both exogenous and endogenous RNM caused the KIR to decrease ( P < 0.01); however, RNM scavengers such as TIP and GSH rescued this phenomenon dose dependently. In conclusion, our data suggests that RNM scavengers such as TIP and GSH enhance the antineoplasmic activity of NK cells.

4740 Introduction To explore the influence of the exogenous and endogenous Reactive Nitrogen Metabolites (RNM)as a NK cell supressor andthe effect of Tiopronin (TIP) A Glutamylcysteinylglycine (GSH) Adihydrochloride (DHT) as immunoadjuvant to reverse RNM's suppressing influence in NK cell-mediated killing of K562 cell line. Methods 1.Exogenous ONOO- was administered in the NK cell and K562 cell culture system, Then TIPAGSH and DHT wereadministered in the cultivated systems espectively. The concentrations of RNM were measured after six hours and the corresponding changes of TNF-βand IFN-γ and K562 cell inhibition rate(KIR) were observed after 24 hours.2. IL-2 and PHA were administered as reactivators in the system of Monocytes(MO) plus NK cells(E) and K562(T) cells (E/T=10/1,E/MO=10/2). Different concentrations of TIP, GSH and DHT were administered in the cultivated systems then the Parameters of NK cell activity include KIR Aproductions of TNF-β and IFN-γ were measured on schedule. Results 1.After exogenous ONOO- was administered in the NK cell and K562 cell culture system, The population and the activty of NK cells degraded significantly. When the TIPAGSH and DHT were administered in the systems, RNM productions dropped from 260.30 ± 9.51 umom/L to 178.65 ± 10.00 umom/L (P<0.05) A185.02± 8.17umom/L (P<0.05), 255.32 ± 11.93 (P>0.05) respectively. The percentage of live NK cells increase form 79.87 ± 1.03% to 91.13 ± 0.67% (P<0.05) A88.03 ± 1.46% (P<0.05) A82.6 ± 0.76% (P>0.05) respectively, KIR increase from 43.84 ± 0.19% to 59.35 ± 1.08% (P<0.05) A56.64 ± 0.83% (P<0.05) A51.41±1.47% (P<0.05) respectivelyGTNF-βAIFN-γ productions increased correspondingly. When TIP,GSH and DHT were administered in the cultivated systems mixing with NK cells,K562 cells,Monocytes,IL-2 and PHA, the trends of parameter changes we measured were like the result of part 1. With higher concentration of TIP and GSH,the RNM productions decreased accordingly, TNF-β and IFN-γ productions as well as KIR increased at the same time,while DHT can not clear RNM. Conclusions Exogenous ONOO-is deleterious to NK cells and K562 cells. Monocytes are the major resource of endogenous RNM. The RNM can disable NK cells in killing K562 cells. Both of TIP and GSH can protect NK cells via scavenging RNM and enhance the anti-neoplasm activity of NK cells. Meanwile,there was a dose-effect relationship between the doses of TIP and GSH and their capability of scavenging RNM,while the DHT cannot scavenge RNM. In scavenging RNM and up-regulating KIR,TIP is as good as GSH, but both of them are better than DHT. Therefore, TIP and GSH may substitude DHT as the immunoadjuvant during the adoptive immunotherapy in leukemia. Disclosures: No relevant conflicts of interest to declare.