Once the "ideal model of the blood-brain barrier" has been designed, one must decide what kind of cells to use for a particular experiment. There are no definitive rules, but one must keep in mind that some conditions are only present in a particular species, as, for example, in the case of humans. However, experiments with dynamic modeling have shown that one of the initiating factors in endothelial cell differentiation consists of cell cycle arrest induced by flow . It is therefore imperative, whatever cells one may decide to use, that these cells themselves be capable of being distracted from the cell cycle by environmental cues.
In fact, if cell lines are to be used, one has to carefully assess their tendency to become either hyperproliferative or immortalized since both conditions will make their differentiation into a mature endothelial phenotype either hard or impossible (Table II). Obviously, cell lines offer numerous advantages, including cost-effectiveness and ease of use. However, with the advent of stem cell research, and our increasing understanding of how blood cells differentiate into endothelial cells, one can envision a future where differentiating factors will be used to induce blood-brain barrier properties in omnipotent stem cells.
Many factors must be taken into consideration if the desire exists to use primary human cultures (Table II). The availability and ease of obtaining human specimens to isolate cells can be a challenging obstacle, unless experiments are performed in proximity to a hospital or similar environment where specimens are readily available. The numbers of cells to be isolated are crucial to running a successful experiment and therefore increase the techniques and time required of the scientist. Although these pitfalls seem major, the benefits of using primary human cultures far outweigh the costs. The main advantages in using primary human cultures are that these cells are not manipulated, allowing the study of the actual disease and its progress. Also, cells can be manipulated as needed for any given experiment. Obtaining human specimens provides a variety of etiologies that otherwise may not be available in cell lines or commercial products. Under normal conditions, primary cells also tend not to divide excessively or take on an "immortal" pheno-type, as often occurs in cell lines.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.