Chicken cystatin stimulates nitric oxide release from interferon‐γ‐activated mouse peritoneal macrophages via cytokine synthesis

Cystatins are natural tight‐binding, reversible inhibitors of cysteine proteases. We have shown that cystatins also stimulate nitric oxide (NO) production by interferon‐γ‐activated mouse peritoneal macrophages [Verdot, L., Lalmanach, G., Vercruysse, V., Hartman, S., Lucius, R., Hoebeke, J., Gauthier F. & Vray, B. (1996) J. Biol. Chem . 271 , 28077–28081]. The present study was undertaken to further document this new function. Macrophages activated with interferon‐γ and then stimulated with interferon‐γ plus chicken cystatin generated increased amounts of NO in comparison with macrophages only activated with interferon‐γ. Interferon‐γ‐activated macrophages must be incubated with chicken cystatin for at least 8 h to upregulate NO production. NO induction was due to increased inducible nitric oxide synthase protein synthesis. Macrophages incubated with chicken cystatin alone or with interferon‐γ plus chicken cystatin produced increased amounts of both tumor necrosis factor α and interleukin 10. The addition of recombinant murine tumor necrosis factor α alone or in combination with recombinant murine interleukin‐10 mimicked the effect of chicken cystatin. The addition of neutralizing anti‐(tumor necrosis factor α) antibodies reduced sharply NO production by chicken cystatin/interferon‐γ‐activated mouse peritoneal macrophages. Taken together, these data suggest that chicken cystatin induces the synthesis of tumor necrosis factor α and interleukin 10. In turn, these two cytokines stimulate the production of NO by interferon‐γ‐activated macrophages. The findings point to a new relationship between cystatins, cytokines, inflammation and the immune response.