Journal of Leukocyte Biology
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Published online before print July 14, 2008
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© by The Society for Leukocyte Biology
Journal of Leukocyte Biology, doi:10.1189/jlb.0308157

Received for publication March 4, 2008.
Revised May 21, 2008.
Accepted for publication June 13, 2008.

Article

Interactions between Shiga toxins and human polymorphonuclear leukocytes

Maurizio Brigotti *@, Domenica Carnicelli *, Elisa Ravanelli *, Stefania Barbieri *, Francesca Ricci {dagger}, Andrea Bontadini {dagger}, Alberto E. Tozzi {ddagger}, Gaia Scavia {sect}, Alfredo Caprioli {sect}, and Pier Luigi Tazzari {dagger}

*Dipartimento di Patologia Sperimentale, Università di Bologna, Italy; {dagger}Servizio di Immunoematologia e Trasfusionale, Ospedale S. Orsola-Malpighi, Bologna, Italy; {ddagger}Ospedale Pediatrico Bambino Gesù, Rome, Italy; and {sect}Dipartimento di Sanità Alimentare e Animale, Istituto Superiore di Sanità, Rome, Italy

@ To whom correspondence should be addressed. E-mail: brigotti{at}alma.unibo.it.


  Abstract

Human intestinal infections by Shiga toxin (Stx)-producing Escherichia coli cause hemorrhagic colitis and hemolytic uremic syndrome (HUS), which represents the main cause of acute renal failure in early childhood. In HUS, Stx released in the gut enter the bloodstream and are targeted to renal endothelium. The mechanism of toxin delivery is still a matter of debate, although the role of polymorphonuclear leukocytes (PMN) as a Stx carrier has been indicated. The aim of this paper was to better define the interactions between Stx and human PMN. Direct and indirect flow cytometric analysis and binding experiments with radiolabeled toxins demonstrated that Stx bind to the surface of human mature PMN but not to immature PMN from G-CSF-treated donors. The use of the human myeloid leukemia cell (HL-60) model for inducible cell differentiation confirmed that the toxin binding occurs only after granulocytic differentiation. Stx binding caused a delay of the spontaneous apoptosis of PMN, as shown by the delayed appearance of apoptotic nuclei and activation of caspase 3 and by the higher number of cells negative to the annexin V-binding assay after 48 h. Moreover, flow cytometric analysis of mixed Stx-positive and Stx-negative PMN populations showed that the toxins were transferred from positive to negative PMN. The delayed, spontaneous apoptosis and the passage of the toxic ligand from older PMN to new, mature cells entering the circulation from the bone marrow may explain the previously reported persistence of Stx in the blood of children with HUS.

Key Words: hemolytic uremic syndrome • neutrophils • HL-60 • apoptosis






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