Epithelial cell coculture models for studying infectious diseases: benefits and limitations

Abstract

Countless in vitro cell culture models based on the use of epithelial cell types of single lineages have been characterized and have provided insight into the mechanisms of infection for various microbial pathogens. Diverse culture models based on disease-relevant mucosal epithelial cell types derived from gastrointestinal, genitourinary, and pulmonary organ systems have delineated many key host-pathogen interactions that underlie viral, parasitic, and bacterial disease pathogenesis. An alternative to single lineage epithelial cell monoculture, which offers more flexibility and can overcome some of the limitations of epithelial cell culture models based on only single cell types, is coculture of epithelial cells with other host cell types. Various coculture models have been described, which incorporate epithelial cell types in culture combination with a wide range of other cell types including neutrophils, eosinophils, monocytes, and lymphocytes. This paper will summarize current models of epithelial cell coculture and will discuss the benefits and limitations of epithelial cell coculture for studying host-pathogen dynamics in infectious diseases.

Figure 1

Examples of coculture models for the study of infection. A. Monolayer cocultures typically incorporate epithelial cells and another adherent cell type(s) and these detect microbes (I) and signal via juxtacrine mechanisms (black arrow) to cells in the monolayer to induce synthesis of immune factors and cytokines. Microbes that bind or invade epithelial cells may induce signals from the partner cell types in the monolayer, which can release inflammatory molecules (II) such as nitric oxide (NO) or reactive oxygen species (ROS). In models that utilize viable microbes overgrowth can lead to cytotoxicity of host cells in the monolayer (III) and may limit the study. B. Suspension cocultures often utilize phagocytes that ingest microbes and signal other cells to proliferate (I). Suspension coculture models sometimes use dynamic conditions such as rolling and may incorporate immature or mature versions of cell lineages such as monocytes or macrophages. Intercellular signalling can occur via juxtacrine pathways (black arrow) where receptors are ligated and can lead to the induction of inflammatory molecules (II). Alternatively, cells may respond to immune factors as co-stimulatory molecules that are required for optimal responses to microbes (III) such as production of regulatory factors. C. Mixed cocultures typically utilize adherent monolayers in combination with a suspension cell type(s), which can respond to co-stimulation by differentiation (I). Microbe binding to suspension cells may lead to cytokine/immune factor signalling of the adherent cells to induce the secretion of inflammatory molecules by the monolayer (II). Phagocytes present in the coculture may ingest microbes and signal to the adherent cells via an unknown receptor mechanism to promote juxtacrine signalling between cells (black arrow) as a means to trigger downstream regulatory factors (III). Microbe binding to adherent cells may stimulate paracrine signalling to suspension cells, recruiting them towards the monolayer (IV).