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2015|16 Annual Report Fraunhofer IGB

8 4 In vitro models for infection research In infection research, in vitro models are well suited for study- ing initial processes in the colonization of epithelial surfaces by pathogens. In particular, adhesion and invasion processes can be studied and analyzed very well using human infection models, as already shown many times by us and others. In ad- dition, these models can be used effectively for screening for new active substances [1]. In this way, effects on human cells can be recorded and thus an initial assessment of the toxic and protective effects of the potential drug can be made at the same time. To date, however, further investigations, in particular on the interaction between pathogens and the immune system, have only been inadequately possible. Here, we are working under the framework of the Marie Curie Initial Training Network “ImResFun” to establish a skin model which not only consists of epidermal and dermal components but also contains im- mune cells. The focus is on understanding how human epithe- lial and immune cells respond to infection and how they com- municate in the defense against pathogens. For this purpose, in this study the novel skin models supplemented with defined immune cell types are infected with the most frequent human fungal pathogens of the species Candida. The aim of the network ImResFun, which consists of 12 partners from nine uropean countries, is to find new means for fighting Candida infections. Immunocompetence by integration of immune cells in 3D skin models In healthy humans, the skin is resistant to symptomatic infec- tions by microorganisms that, like Candida albicans, naturally colonize the skin. Skin infections in general occurring rarely are primarily superficial eeper invasion into subepithelial tissue that would allow C. albicans to access the blood stream leading to systemic spread doesn’t normally occur in humans with intact skin. However, in vitro skin models consisting of keratinocytes as an epidermal layer and fibroblasts embedded in collagen as a dermal layer are penetrated and destroyed very quickly by C. albicans [2]. This is not surprising since these skin models do not contain any components of the immune system. Hence, we developed skin models that also include immune cells. In order to design reproducible skin models that are independent of donor-based differences in primary cells, we built them from immortali ed keratinocytes and fibroblasts Cells known as T cells (T-lymphocytes) that provide immune response to C. albicans in humans as well (Fig. 1) were inte- grated into the models as immune cells. In the presence of T cells, invasion of C. albicans is significantly reduced and even stopped during the observation period. This means that the system shows at least partial immunocompetence in vitro. Immune response in a test tube Using next-generation sequencing, this partial immunocom- petent system was comprehensively studied in dual RNA sequence analyses in the presence and absence of C. albicans. We discovered that none of the individual cell types alone achieved an effective defense against C. albicans infection. Instead, cytokine-mediated communication between the dif- ferent cell types seems to be necessary to trigger an effective antimicrobial response One of the key molecules identified by us in these analyses is the immune receptor TLR2 required IN VITRO INFECTION MODELS WITH IMMUNOCOMPETENCE Andreas Kühbacher, Anke Burger-Kentischer, Kai Sohn, Steffen Rupp PHARMACY 1 84