Epithelial Cell Models

Epithelia are formed by cells in close proximity to each other lying on a basal membrane. This structure is fed through the connective, highly vascularized tissue, which underlies the basal membrane. Epithelia cover every surface of the human organism, either externally or internally, as a monolayer or multilayer structure. External epithelia protect the body surfaces against mechanical damage, prevent the entry of microorganisms and control the loss of water caused by evaporation. Internal epithelia have other functions related to absorption and secretion.

Adhesion to epithelia is the first step in the pathogenesis of the microorganism. Thus, the epithelial cell models employed to study A. fumigatus are pulmonar or bronchoalveolar models while C. neoformans has been tested with olfactory mucosa or pneumocytes as these environmental fungi enter the human body normally by inhalation. There are limited in vitro studies with epithelia that focus on the airborne infections caused by H. capsulatum, although tracheal epithelium has been analysed (Eissenberg et al., 1997). As C. albicans is found as a commensal in the human microbiota it causes endogenously derived infections. Thus, adhesion of the fungus to epithelia of the gastrointestinal or urogenital tract, as well as to the epidermis is a critical first step in this type of infection. Next, invasion may occur. This step can take place at a cellular level when pathogens use a transcellular path to cross the barrier. To observe these processes in complex epithelial in vitro tissue models, modern microscopy assists ultrastructural and histochemical methods.

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