Efficient animal welfare and the implementation of a sustainable 3R concept require both interdisciplinary cooperation between the various disciplines and transdisciplinary dialogue between science, industry, politics and interest groups. The Bundesnetzwerk 3R (www.bundesnetzwerk-3r.de), initiated by the Federal Ministry of Education and Research (BMBF), aimed to provide opportunities for exchange and encounters between the 3R centres in order to promote 3R methodological research in Germany. This network has given rise to the collaboration between the Interdisciplinary Centre for Animal Welfare Research and 3R (ICAR3R) at the Justus Liebig University Giessen and the Virtual Centre for Alternative and Complementary Methods to Animal Experiments (VZET) at the University of Veterinary Medicine Hannover, which focuses on alternative methods for epithelial barriers as part of the One Health concept. Transport processes across physiological barriers represent important physiological functions in many parts of the body. From a qualitative and quantitative point of view, epithelial tissues of the lung, intestine and mammary gland are of major importance. In order to study basic barrier functions in these organs under in vivo conditions, elaborate experiments are required. For these organs, several in vitro experiments have been established in recent years to replace in vivo studies. These experimental approaches will be presented in detail at the 1st joint symposium of the 3R Centres of both universities. On 13th Dezember 2024 this collaboration will be launched with a symposium entitled "Alternative approaches to One Health research for humans and animals in focus - epithelial barriers" at the Justus Liebig University Giessen.