[This is the old program from SS 2006. The current program and contact information can be found here.]

28 April 2006, 16:00

Dorothea Busse (Institut für Biologie, Humboldt-Universität zu Berlin)
Spatio-temporal dynamics of cell signalling  

Abstract:
Interleukin-2 (IL-2) is expressed by T-cells after antigen stimulation and drives T-cell proliferation. Proliferation is necessary for the adaptive immune response to pathogens, but activation by self-antigen can cause autoimmune reactions. Regulatory T-cells (Treg-cells), are known to suppress T-cell activation in vitro and inhibit autoimmune reactions as well as regulate immune responses in vivo. However, the mechanism of interaction between both cell types remains unclear. One hypothesis proposes competition for IL-2 [1]. Therefore understanding the regulation of IL-2 expression and the intercellular communication mediated by IL-2 is of fundamental interest.
IL-2 expression is a complex process involving an autocrine positive feedback loop. To analyse the regulatory properties of the feedback loop, a mathematical model is introduced describing the IL-2 expression of a single T-cell and the extracellular IL-2 diffusion in infinite space. Applying a quasi-steady-state approximation for the IL-2 diffusion, the model is reduced to a system of ordinary differential equation describing the IL-2 receptor dynamics at the plasma membrane. The model exhibits bistability. Consistent with the experimentally observed states, the stable steady-state characterized by a low expression of the IL-2 receptor is interpreted as the resting and the one with a high expression as the activated state. To reach the activated state the strength of the antigen-stimulus must exceed a threshold value. To describe the interaction between both T-cells and T-cells and Treg-cells we extended the model considering two coupled cells. The autocrine and paracrine action in both cases are regulated by the IL-2 and the IL-2 receptor expression rates as well as the cell distance. In proximity for moderate IL-2 expression the interaction between T-cells and Treg-cells leads to a pronounced difference in IL-2 receptor expression, which can explain suppression of autoimmunity by competition and also activation of Treg-cells during an immune response.
[1] De la Rosa, M., et al., (2004), Eur. J. Immunol., 34(9), 2480-8

19 May 2006, 16:00

Karsten Reuter (Abteilung Theorie, Fritz-Haber-Institut der MPG, Berlin)
First-principles statistical mechanics approaches to heterogeneous catalysis [Abstract] 

02 June 2006, 16:00

Blas Echebarría (Departament de Física Aplicada, Universitat Politècnica de Catalunya, Barcelona, Spain)
Instabilities of scroll waves in excitable media [Abstract] 

23 June 2006, 16:00

Hermann Riecke (Department of Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, USA)
Spatio-temporal chaos in convection: defects, bursts, and spirals [Abstract] 

14 July 2006, 16:00

Martin Baurmann (Institut für Chemie und Biologie des Meeres, Carl-von-Ossietzky-Universität Oldenburg)
Pattern formation in microbiogeochemical models [Abstract]