Conclusions from two model concepts on germinal center dynamics and morphology.

Germinal centers (GC) are an essential part of the humoral immune response. They develop a clear structure during maturation: Centroblasts and centrocytes are separated into two zones, the dark and the light zone. The mechanisms leading to this specific morphology as well as the reason for zone-depletion during a later phase of the GC reaction have not clearly been revealed in experiment. We discuss and weigh possible mechanisms of dark and light zone development in the framework of two mathematical models. In a comparative approach we formulate constraints on typical lymphocyte velocities in GCs which are characteristic for the different proposed mechanisms.