Host-Pathogen Interactions ofActinobacillus pleuropneumoniaewith Porcine Lung and Tracheal Epithelial Cells

Abstract

Host-pathogen interactions are of great importance in understanding the pathogenesis of infectious microorganisms. We developed in vitro models to study the host-pathogen interactions of porcine respiratory tract pathogens using two immortalized epithelial cell lines, namely, the newborn pig trachea (NPTr) and St. Jude porcine lung (SJPL) cell lines. We first studied the interactions of Actinobacillus pleuropneumoniae, an important swine pathogen, using these models. Under conditions where cytotoxicity was absent or low, we showed that A. pleuropneumoniae adheres to both cell lines, stimulating the induction of NF-B. The NPTr cells consequently secrete interleukin 8, while the SJPL cells do not, since they are deprived of the NF-B p65 subunit. Cell death ultimately occurs by necrosis, not apoptosis. The transcriptomic profile of A. pleuropneumoniae was determined after contact with the porcine lung epithelial cells by using DNA microarrays. Genes such as tadB and rcpA, members of a putative adhesin locus, and a gene whose product has high homology to the Hsf autotransporter adhesin of Haemophilus influenzae were upregulated, as were the genes pgaBC, involved in biofilm biosynthesis, while capsular polysaccharide-associated genes were downregulated. The in vitro models also proved to be efficient with other swine pathogens, such as Actinobacillus suis, Haemophilus parasuis, and Pasteurella multocida. Our results demonstrate that interactions of A. pleuropneumoniae with host epithelial cells seem to involve complex cross talk which results in regulation of various bacterial genes, including some coding for putative adhesins. Furthermore, our data demonstrate the potential of these in vitro models in studying the host-pathogen interactions of other porcine respiratory tract pathogens.

Regulation of pga Operon Expression and Biofilm Formation in Actinobacillus pleuropneumoniae by σ E and H-NS

“…As expected, pgaA expression in M2000 was similar to that seen in the rseA::Km and hns::Km mutants of S4074 T . Auger et al (2) recently showed that the pgaBC genes were upregulated in A. pleuropneumoniae following contact with porcine respiratory tract epithelial cells, indicating that biofilm formation may contribute to colonization and/or persistence of this bacterium in vivo.…”

Outer Membrane Protein A of Bovine and Ovine Isolates of Mannheimia haemolytica Is Surface Exposed and Contains Host Species-Specific Epitopes

“…Longer loops have also been correlated with virulence in neisserial species, where commensal organisms have shorter hypervariable domains (and thus shorter loops) than pathogenic species (51). There is evidence to suggest that in a number of bacterial species the capsule can be downregulated upon contact with host cells (2,15,26) and as a consequence of phase-variable expression (4,29,43), thus allowing transient exposure of OMP adhesins. Also, blebbing of outer membrane vesicles has been observed in several Gram-negative bacteria (reviewed in reference 44), allowing OMPs to traverse the capsule and reach the extracellular environment.…”

“…Indeed, an acapsular serotype A1 M. haemolytica mutant was shown to have greater fibronectin-binding activity than that of the capsular parental strain, suggesting a shielding role of the capsule. In other species, CPS may be downregulated upon contact with host cells (2,15,26) or as a consequence of phase-variable expression (4,29,43), thus allowing transient exposure of outer membrane adhesins. The shielding of OMPs, including OmpA, by CPS is likely to have important implications for the function of surface proteins but has yet to be investigated in M. haemolytica.…”

Investigation of the Species Origin of the St. Jude Porcine Lung Epithelial Cell Line (SJPL) Made Available to Researchers

“…Following the first report of the SJPL cells (5), other investigators have used these cells in their studies (1,4,6,7; C. A. Gagnon and M. Jacques, 9 December 2008, international patent application PCT/CA2008/001953). In some of those reports, the SJPL cells were used as a model to study viral and bacterial pathogenesis in regard to the respiratory tract environment of the susceptible host (1, 7).…”