Dissertation submitted to the Combined Faculties for the Natural Sciences and for Mathematics of the Ruperto-Carola University of Heidelberg, Germany for the degree of Doctor of Natural Sciences Presented by Dipl. Biol. Oezcan Talay Born in Ankara, Turkey Oral examination: Efficient Dendritic Cell Maturation and Initiation of a Strong T Cell Immune Response Requires B7-H1-Mediated Dendritic Cell ‘Conditioning’ During Interaction with T Cells. Referees: Prof. Dr. Volker Schirrmacher ``` Prof. Dr. Jianzhu Chen In Loving Memory of my Father. Science cannot solve the ultimate mystery of nature. And that is because, in the last analysis,we ourselves are part of the mystery that we are trying to solve.