AbstractEffects on host defenses of Total Parenteral Nutrition (TPN) with long-(LCT) and medium-chain triglycerides (MCT) were studied.Survival to lipopolysaccharide (LPS) challenge, blood clearance ofEscherichia coli, in vivoandin vitroproduction of tumor necrosis factor-α(TNF-α) and interleukin-6 (IL-6) were investigated.In BALB/c mice, LCTs produced a 25% reduction in mortality, compared with controls. TPN performed with a LCT plus MCT mixture reduced mortality by 50%. Spasms appeared after 18 h and 12 h respectively in mice treated with LCT-MCT mixture or LCTs alone, respect to controls (8 h). The LCT-MCT mixture produced a 67% blood clearance ofE. coliafter 1 h, while the treatment with LCTs alone had no significant effects compared to controls (about 40%). The LCT-MCT mixture induced a 50% increase in chemiluminescence respect to controls. A 33% increase was observed in rats treated with LCTs alone. TNF-αserum levels after challenge with LPS were not modified by any of the triglycerides or their combinations. IL-6 increased by 43% with LCT-MCT mixture and by 39% with LCTs aloneversuscontrols. After a 3 hin vitrotreatment with LCTs, human monocytes were stimulated to release TNF-αat levels higher than those stimulated with the LCT-MCT mixture, and respect to controls. In contrast after 3 h the stimulation with LCT-MCT mixture induced a higher IL-6 release than controls and cells stimulated with LCTs alone, or with LPS.