Primary porcine respiratory epithelial cell models used in the PIGSs project to study host–pathobiont interactions in the respiratory tract: PCLS model.

The PIGSs project aims to improve our current understanding of the interplay of commensals, pathobionts, and keystone pathogens in the respiratory tract. Studies to dissect these complex processes should be carried out in respective animal models, e.g., in pigs, or under conditions which most closely mimic in vivo conditions. Since animal experiments have limitations for several reasons, ex vivo/in vitro tissue cell culture models receive more and more attention. Two of such models based on primary porcine respiratory epithelial cells are air–liquid-interface (ALI) cultures and precision-cut lung slice (PCLS). Both have been shown to be suitable to study host–pathobiont interactions of S. suis in the porcine respiratory tract


For soft tissue such as lung, which is closely inter-networked by extracellular matrix and honeycombed to enable maximal gas exchange, it is technically challenging to obtain PCLS. However, a major breakthrough was achieved by Placke and Fisher in 1980s by infusion of the airways of hamster and rat lungs. In general, PCLS are prepared to a thickness of 100–500 μm and are reproducible tools which can be deployed in a variety of ex vivo experimental protocols. 


The advantage of the ex vivo PCLS model is that it preserves the structural and functional integrity of the lung, including the ciliary activity at the bronchiolar surface, since those slices are pieces of lung tissue which can be kept in cell culture medium for several days. PCLS have been proved to be convincing alternatives to in vivo experiments for physiological, pharmacological, and toxicological investigations. This method allows to investigate the adherence, colonization, and invasion of pathogens and to study microbial effects on bronchial epithelial cells, e.g., the ciliary motility and bronchus-constriction, by light microscopy. A limitation of PCLS is the restricted time of viability of the cells, making it less suitable for studying long-term effects.


Air–liquid-interface (ALI) cultures (see next news item) and PCLS as well as further models, such as organoids from the respiratory tract, will have to be further improved, e.g., by including immune cells. Such models and respective imaging techniques will enable researchers in the future to dissect the complex interactions of microbes on mucosal surfaces with each other and the host, which will contribute to a better understanding of the role that pathobionts play in infection processes in the airway system.


Figure: a precision-cut lung slice (PCLS)


The University of Veterinary Medicine Hannover (TiHo), partner in the PIGSs project, is in charge of developing and maintaining this PCLS model. 


More information about this in vitro model can be found in the following publication: 

Vötsch D, Willenborg M, Weldearegay YB and Valentin-Weigand P (2018) Streptococcus suis – The “Two Faces” of a Pathobiont in the Porcine Respiratory Tract. Front. Microbiol. 9:480. doi: 10.3389/fmicb.2018.00480