Depletion of liver and splenic macrophages reduces the lethality of Shiga toxin-2 in a mouse model

The haemolytic uraemic syndrome (HUS) is a clinical syndrome consisting of haemolytic anaemia, thrombocytopenia, and acute renal insufficiency. HUS is the most frequent cause of acute renal failure in childhood. It has been p reviously suggested that the presence of Shiga toxin (Stx) is necessary but not sufficient for HUS development, and cytokines such as tumour necrosis factor-alpha (TNF-alpha) and IL-1 beta appear to be necessary to develop th e syndrome. Since the mononuclear phagocytic system (MPS) is the major sour ce of these cytokines, macrophages might be one of the relevant targets for Stx action in the pathophysiology of HUS. In this study our objective was to examine the role of the hepatic and splenic macrophages in a mouse model of HUS induced by injection of Shiga toxin type-2 (Stx2) or Stx2 plus lipo polysaccharide (LPS). For this purpose, depletion of mice macrophages by li posome-encapsulated clodronate (lip-clod), followed by injection of STx2 or Stx2 plus LPS, was assayed. In this study we show that depletion of hepati c and splenic macrophages by clodronate treatment induces a survival of 50% in animals treated with Stx2 alone or in presence of LPS. This maximal eff ect was observed when lip-clod was injected 48-72 h before Stx2 injection. Biochemical and histological parameters show characteristics of the lesion produced by Stx2, discarding non-specific damage due to LPS or lip-clod. In addition, we determined that the toxic action of Stx2 is similar in BALB/c and N:NIH nude mice, indicating the T cell compartment is not involved in the Stx2 toxicity. Briefly, we demonstrate that macrophages play a central role in the pathophysiology of HUS, and that the systemic production of cyt okines by liver and/or spleen is for Stx2 to manifest its full cytotoxic ef fect. In addition, the toxicity of Stx2 alone, or in presence of LPS, is in dependent of the T cell compartment.