**Acknowledgements**

Ralf Weiskirchen is supported by the German Research Foundation (SFB/TRR 57, projects P13 and Q3) and the Interdisciplinary Centre for Clinical Research within the Faculty of Medicine at the RWTH Aachen University (IZKF Aachen, project E7-6). None of the funding sources were involved in the writing of the report or in the decision to submit this book chapter for publication.
