Renalase is widely expressed in glomeruli, tubules, mesangial cells, podocytes and tubular epithelial cells, but its physiological function is not clear yet. Further studies about this novel protein's molecular structure as well as function, carry a great value. At present, a lot more works need to be done on renalase's expression, regulation, function and replacement therapy etc.  Virus contaminations of cell cultures – A biotechnological view In contrast to contamination by microbes and mycoplasma, which can be relatively easily detected, viral contamination present a serious threat because of the difficulty in detecting some viruses and the lack of effective methods of treating infected cell cultures. While some viruses are capable of causing morphological changes to infected cells (e.g. cytopathic effect)which are detectable by microscopy some viral contaminations result in the integration of the viral genome as provirus, this causes no visual evidence, by means of modification of the cellular morphology. Virus production from such cell lines, are potentially dangerous for other cell cultures (in research labs)by cross contaminations, or for operators and patients (in the case of the production of injectable biologicals) because of potential infection. The only way to keep cell cultures for research, development, and the biotech industry virus-free is the prevention of such contaminations. Cell cultures can become contaminated by the following means: firstly, they may already be contaminated as primary cultures (because the source of the cells was already infected), secondly, they were contaminated due to the use of contaminated raw materials, or thirdly, they were contaminated via an animal passage. This overview describes the problems and risks associated with viral contaminations in animal cell culture, describes the origins of these contaminations as well as the most important virsuses associated with viral contaminations in cell culture. In addition, ways to prevent viral contaminations as well as measures undertaken to avoid and assess risks for viral contaminations as performed in the biotech industry are briefly described. Since the development of viral vaccines, animal cell technology has been used for the production of biologicals for prophylaxis and therapy of humans and animals. As many of these products are injectables, the microbiological safety is of particular importance and is a permanent concern. Whereas microbial contaminations (fungi, yeasts, and bacteria) can be rather easily detected via cultivation methods, the detection of mycoplasma and viruses is more difficult because they are not observable by routine light microscopy. However, fluorescence microscopy, mycoplasma amplification and culture techniques, ELISA and PCR are well developed for determining the extent of mycoplasma contamination. Viral contamination, on the other hand, represents a greater concern because viruses require more complex and frequently need highly sophisticated detection methods (see later). In addition the potential for viruses to cause silent infection of cell culture needs to be addressed, negative results do not always signify that there is no virus contamination. Viral infection can originate from contaminated cell lines, contaminated raw materials, or from a GMP breakdown in the production and purification process (Minor, 1996) leading to a virus-contaminated final product. In addition, although downstream processing is able to eliminate or inactivate certain viruses, not all viruses can be eliminated in such a way because they can be resistant to elimination and/or inactivation steps. Viral infection can be highly pathogenic, and in contrast to microbial infection, there are frequently no effective treatments available, this requires serious consideration to be given to the prevention of contamination. As a result of this everything possible has to be done in order to maintain the entire manufacturing process, and thus the final product, virus-free.