Studies on the interactions of Haemophilus parasuis with porcine epithelial tracheal cells: limited role of LOS in apoptosis and pro-inflammatory cytokine release.

Haemophilus parasuis colonizes the upper respiratory tract of swine and causes Glässer's disease. We recently demonstrated that H. parasuis can adhere to newborn pig tracheal (NPTr) cells. However, the molecular mechanisms involved in upper respiratory tract colonization by H. parasuis are unknown. The aim of this work was to investigate the role of H. parasuis lipooligosaccharide (LOS) in bacterial adhesion to NPTr cells, the ability of the bacteria and its LOS to induce NPTr cells apoptosis, and their stimulating effect on cytokine release. Our results showed that LOS is partially involved in adhesion to NPTr cells. H. parasuis induced NPTr cells apoptosis in a caspase-3 dependent fashion, but LOS did not seem to be involved in such a process. H. parasuis and, to a lesser extent, its LOS stimulated IL-8 and IL-6 release by NPTr cells. In addition, H. parasuis serotype 4 field isolates induced higher levels of these mediators than did serotype 5 isolates. These results suggest that bacterial adhesion, induction of apoptosis and cytokine release are important events for H. parasuis colonization, but LOS appears to have a limited role in these processes.