Schematic representation of various in vitro BBB and BCSFB models. The BBB models are built up around endothelial cells, whereas the BCSFB models rely on epithelial cell culture. The setup can be a monoculture: endothelial or epithelial cells only (a, b, and g); coculture: endothelial cells with epithelial cells (h) or endothelial cells with pericytes or astrocytes (c and d); and triple-culture: endothelial in combination with astrocytes and pericytes (e and f). These systems can be set up in a “contact” (e, f, and h) or “noncontact” (c and d) manner (“contact”: different cell types have physical contact with each other; “noncontact”: different cell types were not able to physically interact with each other). The monoculture models represented in (a) and (b) can also be used with epithelial cells instead of endothelial cells. The addition of chemical mediators (cytokines and/or chemokines) and virus or immune cells (T-, B-cells, and PMNs, etc.) is possible in both the filter insert and/or well.