Flagellin delays spontaneous human neutrophil apoptosis

JUAN FUXMAN BASS; GABRIELA SALAMONE; YANINA PETRACCA; MARÍA LAURA GABELLONI; JORGE GEFFNER; MARTÍN RUMBO; KAREN NAHMOD; SERGIO ROSENZWEIG; ANALÍA TREVANI

Río de Janeiro, Brasil

Congreso; 13th International Congress of Immunology; 2007

International Union of Immunological Societies

We here examined the ability of flagellin from S. typhimurium (Fg) to modulate neutrophil survival. Dose-dependent studies showed that Fg inhibits spontaneous neutrophil apoptosis after 24 h of culture at concentrations ranging from 1 to 100 ng/ml (% of apoptosis evaluated by fluorescent microscopy: 55±9, 42±11, 21±5 and 18±4, in the presence of Fg 0, 1, 10 and 100 ng/ml respectively; n=6, p<0,05). Similar results were obtained when apoptosis was quantitated by analyzing the % of annexin-V+ cells by FACs. The Fg-mediated antiapoptotic effect (10 ng/ml) was detected in 24-, 48- and 72-h cultures and was not significantly different from the effect mediated by the antiapoptotic cytokine GM-CSF (10 ng/ml) (% apoptosis after 48 h of culture: 88±2, 58±4 and 52±5 for controls, Fg-stimulated and GM-CSF-treated neutrophils, n=6, p<0,05 for Fg-stimulated or GM-CSF-treated vs control cells). Analysis of signalingpathways by western blot revealed that Fg triggered NF-kappaB translocation and induced the activation of PI3k/akt and the MAPKs p38 and ERK1/2 pathways. Additional experiments indicated that the activation of these pathways paralleled neutrophil activation evaluated by the ability of Fg to induce IL-8 production (pg/ml IL-8: 218±64 and 2857±890 for unstimulated and Fg-stimulated -100 ng/mlneutrophils, p<0,01, n=8) and cell shape change (% shape change: 28±8,p<0,05, n=6). Taken together, these findings indicate that Fg induces human neutrophil activation and delays spontaneous apoptosis.Further studies are currently being undertaken to determine the molecular pathways involved in the regulation of neutrophil survival mediated by Fg.