Organotypic Tissue Model Systems for Investigating Host-Pathogen Interactions <em>In Vitro</em>

Recapitulating the host-pathogen interface at the epithelial or mucosal barrier in vitro remains a challenging prospect for infection biologists. While in-house grown 2D epithelial monolayers lack true representation of the in vivo situation, commercially available tissue models are often overlooked due to their cost and practicality. However, with careful planning, such models provide reproducible platforms for a vast array of different applications. Here, we report the use of epithelial models that can be utilized for a wide variety of experimental purposes to investigate host-pathogen interactions in various ecological niches, such as the oral cavity, skin, and vaginal mucosa. From simple planktonic cells to complex biofilm co-culture, epithelial models are used to assess microbial adherence and invasion, and to evaluate the host response at a transcriptional and/or protein level, with scope for more detailed profiling using different omics approaches. Furthermore, these biological systems can be used as more accurate test beds for evaluating conventional and novel antimicrobial activity in a complex host-pathogen microenvironment in vitro. The protocols described herein document how models are handled upon arrival and prepared in the laboratory for co-culture stimulation with biofilm communities. The methods detail how experimental outputs are achieved from the model systems, including the processing of tissue, the co-culture setup, and data generation. These experiments include host gene expression through single- and multiplex qPCR analyses and inflammatory protein detection using ELISAs. In conclusion, epithelial models provide useful in vitro systems for preclinical investigatory studies into simple or complex host-pathogen interactions.