Avian influenza virus (AIV) infections of the chicken occur via the respiratory route. Unlike ducks which are considered as a natural AIV reservoir, chickens are highly susceptible to AIV infections and do not possess the RIG-I pattern recognition receptor involved in triggering the antiviral interferon response. To study the chicken innate immune response to AIV in the respiratory tract, we established an epithelial cell line (CLEC213) from lung explants of white leghorn chickens. CLEC213 cells exhibited a polyhedral morphology and formed cohesive clusters bound through tight junctions as assessed by electron microscopy. Expression of E-cadherin but not vimentin could be detected as expected for cells of epithelial origin. In addition, CLEC213 cells showed characteristics similar to those of mammalian type II pneumocytes, including the presence of intracytoplasmic vacuoles filled with a mucopolysaccharide material, alkaline phosphatase activity, transcription of chicken lung collectins genes (cLL and SPA), and some intracytoplasmic lamellar-like bodies. CLEC213 cells showed a constitutive expression level of TLR3 and TLR4 and were responsive to stimulation with the respective agonists, poly (I:C) and LPS: between 4h and 24h after treatment, a strong increase in the expression of IFN-α, IFN-β and IL-8 genes could be detected. Furthermore, CLEC213 cells supported efficient growth of the low pathogenicity avian influenza virus H6N2 (A/duck/France/05057a/2005) in the presence or the absence of trypsin in the culture media. At 4h post-infection, the H6N2 virus induced highly elevated levels of expression of IFN-α and IL-8, moderately elevated levels of LITAF, TGF-β4 and CCL5. However, an increase of IFN-β gene expression could not be detected in response to AIV infection. In conclusion, like mammalian type II pneumocytes, CLEC213 are able to mount a robust cytokine and chemokine immune response to microbial patterns and viral infection. We hypothesize that they could derive from lung atrial granular cells. The involvement of such type of lung epithelial cells in the respiratory tract defence of the chicken can thus be further studied.

Extra-intestinal pathogenic Escherichia coli (ExPEC) strains are responsible for a wide range of diseases in humans and animals. Using in vitro invasion assays and transmission electron microscopy, we showed that BEN2908, an ExPEC strain of avian origin (also termed APEC for Avian Pathogenic E. coli), is able to usurp cellular endocytic pathways to invade A549 human type II pneumocytes and LMH avian hepatocytes where it is able to survive over several days. Although type 1 fimbriae are the major adhesin of BEN2908, proportions of adherent fimbriated or afimbriated bacteria that entered cells were comparable. Internalization of BEN2908 into human pneumocytes reinforces previous studies indicating that APEC strains could represent a zoonotic risk.