VtaA8 and VtaA9 from <it>Haemophilus parasuis</it> delay phagocytosis by alveolar macrophages

• Main Authors: Costa-Hurtado Mar, Ballester Maria, Galofré-Milà Nuria, Darji Ayub, Aragon Virginia
• Format: Article
• Language: English
• Published: BMC 2012-07-01
• Series: Veterinary Research
• Online Access: http://www.veterinaryresearch.org/content/43/1/57

<p>Abstract</p> <p><it>Haemophilus parasuis,</it> a member of the family <it>Pasteurellaceae,</it> is a common inhabitant of the upper respiratory tract of healthy pigs and the etiological agent of Glässer’s disease. As other virulent <it>Pasteurellaceae</it>, <it>H. parasuis</it> can prevent phagocytosis, but the bacterial factors involved in this virulence mechanism are not known. In order to identify genes involved in phagocytosis resistance, we constructed a genomic library of the highly virulent reference strain Nagasaki and clones were selected by increased survival after incubation with porcine alveolar macrophages (PAM). Two clones containing two virulent-associated trimeric autotransporter (VtaA) genes, <it>vtaA8</it> and <it>vtaA9</it>, respectively, were selected by this method. A reduction in the interaction of the two clones with the macrophages was detected by flow cytometry. Monoclonal antibodies were produced and used to demonstrate the presence of these proteins on the bacterial surface of the corresponding clone, and on the <it>H. parasuis</it> phagocytosis-resistant strain PC4-6P. The effect of VtaA8 and VtaA9 in the trafficking of the bacteria through the endocytic pathway was examined by fluorescence microscopy and a delay was detected in the localization of the <it>vtaA8</it> and <it>vtaA9</it> clones in acidic compartments. These results are compatible with a partial inhibition of the routing of the bacteria via the degradative phagosome. Finally, antibodies against a common epitope in VtaA8 and VtaA9 were opsonic and promoted phagocytosis of the phagocytosis-resistant strain PC4-6P by PAM. Taken together, these results indicate that VtaA8 and VtaA9 are surface proteins that play a role in phagocytosis resistance of <it>H. parasuis.</it></p>