We have described previously a murine model of multinutrient undernutrition that reproduced the features of moderate human malnutrition and led to increased early dissemination of Leishmania donovani. Peritoneal cells from these malnourished mice produced decreased NO after stimulation with IFN-gamma/LPS. We hypothesized that malnutrition may cause a deficit in NF-kappaB activation, a principal transcription pathway for inducible NO synthase and proinflammatory cytokines. Macrophages from malnourished mice, stimulated with IFN-gamma/LPS, showed increased IL-6 production and decreased IL-10 and TNF-alpha production. Neutralization of TNF-alpha in macrophage cultures from the control mice mimicked the effect of malnutrition on NO and IL-10 production, whereas supplemental TNF-alpha added to cultures of macrophages from malnourished mice increased NO secretion. NF-kappaB nuclear binding activity in macrophages from the malnourished mice was reduced early after stimulation, but increased to supranormal values by 16- or 24-h poststimulation. Blocking NO production in the macrophages from the control mice reproduced the effect of malnutrition on the late activation of NF-kappaB, whereas supplemental NO decreased the late NF-kappaB activation in the malnourished mice. Thus, in macrophages from the malnourished mice, initial deficits in NF-kappaB activity probably lead to decreased TNF-alpha, which results in decreased NO; however, IL-6 is regulated independently from NF-kappaB and TNF-alpha. The late activation of NF-kappaB in the macrophages from malnourished mice is due to absence of negative feedback from NO.