The inhibitory effect of T6 cells on the proliferation of erythroleukemic cells is partially mediated through the NO pathway. (A) RT-PCR analysis of iNOS and eNOS expression in spleens (n = 3) isolated from Tr/Tr and H/H mice. Normal Balb/c splenic RNA was used as control. (Bottom panel) Real-time PCR ratios (RTR) for iNOS and eNOS in the isolated spleens. (B) RT-PCR analysis of iNOS expression in T6 cells after 2 days of incubation with the indicated cytokines. An untreated T6 cell sample was designated as a control. (C) Effects of the iNOS inhibitor, 1400W, on the proliferation of erythroleukemic cells. CB3 cells were cultured in the presence of 10% FBS and T6 supernatant (10%), T6 supernatant + 1400W or 1400W alone. The number of viable cells was determined at the indicated time points using the trypan blue exclusion assay. (D) Balb/c neonates were infected with F-MuLV. At 5 weeks after infection, mice were treated daily with SNP (10 μg/100 μL) or PBS for a period of 2 weeks. At the end of treatment, mice were killed, and spleen weights (D) and hematocrit values (E) were determined. *Significant difference between the 2 groups. Error bars represent ± SD. (F) PV patient serum inhibits the growth of human erythroleukemia in culture. HEL cells (10⁴) were cultured in the presence of 10% FBS and either normal or PV patient serum with or without 1400W (10 μM). Viable cells were counted on the indicated days using trypan blue exclusion assay. Graphs show the effect of serum from PV patient 1 (PV1) and normal person 1 (N1).