Intravenous injection of Klebsiella 03 lipopolysaccharide (LPS) into BALM mice induces an anaphylaxis-like shock within minutes. Using 5-hydroxytryptamine as a marker for platelets, we previously suggested that a rapid platelet accumulation in the liver and lung precedes the shock, and that a complement-dependent platelet-degradation is involved in the shock. Here, we examined (i) the effect of platelet-depletion (using an anti-platelet monoclonal antibody) on the shock and (ii) the contribution of macrophages to the platelet-accumulation in those organs. LPS-induced platelet-accumulations in the liver and lung were confirmed by immunostaining. In platelet-depleted mice, the shock was largely prevented. The number of F4/80-positive macrophages was much greater in liver than in lung, and the hepatic macrophages were largely lost in mice given clodronate-encapsulated liposomes. In mice treated with such liposomes, both the LPS-induced accumulation of platelets in the liver (but not in the lung) and the shock were largely prevented, and repopulation of hepatic macrophages restored these LPS-induced responses. These results suggest that (i) platelets are indeed involved in the shock, (ii) Kupffer cells mediate the hepatic platelet accumulation, and (iii) preventing this hepatic accumulation can largely prevent rapid shock being induced by LPS (at the dose used here). (c) 2005 Elsevier B.V. All rights reserved.