When the intracellular pathogen Listeria monocytogenesinfects cultured human mucosecreting polarized HT29-MTX cells apically, it induces the stimulation of mucus exocytosis without cell entry. Using a set of isogenic mutants and purified listeriolysin O (LLO), we identified the L. monocytogenes thiol-activated exotoxin LLO as the agonist of mucus secretion. We demonstrated that the LLO-induced mucus exocytosis did not result from the LLO membrane-damaging activity. We found that LLO-induced mucus exocytosis is an event requiring the binding of LLO to a brush border-associated receptor and membrane oligomerization of the exotoxin. By a pharmacological approach, we demonstrated that no regulatory system or intracellular transducing signal known to be involved in control of mucin exocytosis was activated by LLO. Based on the present data, the stimulatory action of LLO on mucin exocytosis could be accounted for either by an unknown signaling system which remains to be determined or by direct action of LLO with the membrane vesicle components involved in the intracellular vesicular transport of mucins.

-Pestiviruses have been isolated from live sheep pox Tunisian vaccines. Vaccination with these vaccines caused outbreaks of Border Disease in Tunisia. In order to study more precisely the pathogenicity of these isolates, three groups of eight four month old lambs from a pestivirus-free flock were infected by the intratracheal route with a French strain (AV) and two Tunisian isolates (SN3G and Lot21). Clinical, hematological, immunological and virological parameters were evaluated. The three groups developed mild fever and leucopaenia by day 3 to 6 post infection (pi). The differences in the weight curves were not significant. Viruses were isolated from the peripheral blood buffy coat cells by day 4 to 9 pi. Antibodies were present on day 16 pi following infection by the French strain and on day 21 pi with the Tunisian isolates. The results demonstrated that SN3G and Lot21 are almost similar to the French strain used as the reference strain. In field conditions, they could induce economical losses in naive flocks, alone or in association with other pathogens. (33) 492943701; e-mail: p.russo@sophia.afssa.fr 8 agneaux de 4 mois issus d'un troupeau indemne de pestivirus ont été infectés par voie intratrachéale avec une souche française de référence (AV) et 2 isolats tunisiens (SN3G et Lot21). Les données cliniques, hématologiques, immunologiques et virologiques ont été suivies. Les 3 groupes ont développé une légère hyperthermie et une leucopénie entre le 3 e et le 6 e jour post inoculation (pi). Les courbes de poids ne montraient pas de différence significative. Des pestivirus ont été isolés à partir des cellules blanches du sang périphérique entre le 4 e et le 9 e jour pi. Des anticorps ont été mis en évi-dence 16 jours pi avec la souche française et 21 jours pi avec les isolats tunisiens. L'ensemble des ré-sultats a montré que les 2 isolats tunisiens ont un pouvoir pathogène presque similaire à celui de la souche française; ils pourraient provoquer, dans les conditions du terrain, des pertes économiques, seuls ou en association avec d'autres agents pathogènes.Pestivirus / ovin / vaccins anti-clavelée / pouvoir pathogène