Nitric oxide production in SJL mice bearing the RcsX lymphoma: a model for in vivo toxicological evaluation of NO.

SJL mice spontaneously develop pre-B-cell lymphoma that we hypothesized might stimulate macrophages to produce nitric oxide (NO.). Transplantation of an aggressive lymphoma (RcsX) was used to induce tumor formation. Urinary nitrate excretion was measured as an index of NO. production and was found to increase 50-fold by 13 days after tumor injection. NO. production was prevented by the addition of a nitric oxide synthase (NOS) inhibitor. The expression of inducible NOS (iNOS) in various tissues was estimated by Western blot analysis and localized by immunohistochemistry. The synthase was detected in the spleen, lymph nodes, and liver of treated but not control mice. To assess whether the iNOS-staining cells were macrophages, spleen sections from ResX-bearing animals were costained with anti-iNOS antibody and the anti-macrophage antibody moma-2. Expression of iNOS was found to be limited to a subset of the macrophage population. The concentration of gamma-interferon, a cytokine known to induce NO. production by macrophages, in the serum of tumor-bearing mice, was measured and found to be elevated 25-fold above untreated mice. The ability of ResX-activated macrophages to inhibit splenocyte growth in primary culture was estimated and macrophage-derived NO. was found to inhibit cell division 10-fold. Our findings demonstrate that ResX cells stimulate NO. production by macrophages in the spleen and lymph nodes of SJL mice, and we believe this experimental model will prove useful for study of the toxicological effects of NO. under physiological conditions.