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The NKT cell ligand α‐galactosylceramide and its synthetic homologue KRN7000 stimulate rapid and copious secretion of IFN‐γ and TNF‐α release, both of which are key mediators of LPS‐induced shock. We showed that KRN7000, injected before or within 2 h after LPS challenge, was able to prevent endotoxic shock. KRN7000 induced survival when the mice were injected 6, 9, or 12 days before the first injection of LPS, and this protective effect was associated with reduction upon subsequent challenge in the levels of IFN‐γ, TNF‐α, MCP‐1, and an increase of IL‐10. Further analysis showed that the animals treated with KRN7000 prior to LPS challenge had lower numbers of F4/80+, NKT, and NK cells and lower percentages of NKT cells that stained for intracytoplasmic IFN‐γ when compared with mice that were not treated with KRN7000. When MCP‐1 was injected in KRN7000‐treated mice, the lethal effect of LPS challenge was restored, and the numbers of F4/80+, NKT, and NK cells increased to levels similar to those in untreated mice following LPS challenge. Taken together, our data demonstrated that KRN7000, injected from 6 to 12 days before the first administration of LPS, prevented endotoxin shock by inhibiting IFN‐γ, TNF‐α, and MCP‐1 release.

α−galactosylceramide, a natural killer T cell ligand, and its synthetic homolog, KRN7000, consistently influence IFN‐γ and TNF‐α release, both mediators of LPS‐induced shock. To modify the course of endotoxin shock, we injected KRN7000 at different time points of experimental systemic Shwartzman reaction. Mice treated with KRN7000 survived when it was injected within 2 h before and after LPS challenge. Mice survival was associated with low levels of T helper 1 (Th1) cytokines, such as IFN‐γ and TNF‐α. By contrast, protection from endotoxin shock was associated with an increase of T helper 2 (Th2) cytokines, like IL‐4 and IL‐10. A role of Th2 cytokines in counteracting LPS‐induced shock was supported by experiments in which the protection against Shwartzman reaction by KRN7000 was abrogated by in vivo coadministration of anti‐Th2 cytokines antibodies. In addition, cytofluorimetric analysis showed that surviving animals have higher percentages of NKT‐IL‐10‐positive cells and lower percentages of NKT‐IFN‐γ and macrophages/TNF‐α‐stained cells than nonprotected mice. Taken together, our data demonstrate that KRN7000 treatment given at times near LPS challenge is protective for endotoxin shock inhibiting IFN‐γ and TNF‐α release. Moreover, KRN7000‐mediated protection occurs through an increased production of IL‐4 and IL‐10, which are mainly secreted by NKT cells. Since IFN‐γ release by NKT requires a longer TCR stimulation than that required for Th2 cytokines production, we demonstrate that timing of KRN7000 in vivo exposure affect the pattern of cytokines expression protecting animals by endotoxin shock.