As one of the virulence factors of Bacillus anthracis, lethal toxin (LT) induces various pathogenic responses including the suppression of the coagulation system. In this study, we observed that LT markedly increased the circulating soluble P-selectin (sP-sel) levels and microparticle (MP) count in wild-type but not P-selectin (P-sel, Selp-/-) or P-sel ligand-1 (PSGL-1, Selplg-/-) knockout mice. Because sP-sel induces a hypercoagulable state through PSGL-1 pathway to generate tissue factor-positive MPs, we hypothesized that the increase in plasma sP-sel levels can be a self-rescue response in hosts against the LT-mediated suppression of the coagulation system. In agreement with our hypothesis, our results indicated that compared with wild-type mice, Selp-/- and Selplg-/- mice were more sensitive to LT. In addition, the recombinant sP-sel treatment markedly ameliorated LT-mediated pathogenesis and reduced mortality. As a result, elicitation of circulating sP-sel is potentially a self-rescue response, which is beneficial to host recovery from an LT-induced hypocoagulation state. These results suggest that the administration of sP-sel is likely to be useful in the development of a new strategy to treat anthrax.
Keywords: P-selectin ligand 1; Soluble P-selectin; anthrax lethal toxin; hemostasis; microparticle.