Prof. Dr. Michael Reth

Molekulare Immunologie
Fakultät für Biologie
Albert-Ludwigs-Universität Freiburg
und MPI-IE
Stübeweg 51    
79108 Freiburg    

Tel. +49 (0) 761 5108 420    
michael.reth@bioss.uni-freiburg.de    

Project summary:

The resting state of B lymphocytes

Currently, most studies of B lymphocytes deal with the activation, proliferation and differentiation processes of these cells whereas little is known about the mechanisms that ensures that the majority of B lymphocytes of the immune system remain silent before they meet their cognate antigen. Similarly, we know many signalling elements of the activated B cell antigen receptor (BCR) but very few elements interacting with the BCR on resting B cells. We think that without a better knowledge of the resting state, one can neither fully understand the activation state of B cells nor pathogenic alterations associated with hyperactive B cells and autoimmunity.

We have found that the BCR on resting B cells forms an autoinhibited oligomer and that a mutant BCR, which cannot form the oligomer, is hyperactive. Interestingly, B cells are not only activated by the binding to antigen, but also when exposed to the actin polymerization inhibitor latrunculin A (Lat-A). This suggests that the actin cytoskeleton plays an important role in guarding the resting state of the BCR. With a new biochemical strategy, we want to purify the resting BCR together with its associated cytoskeletal binding partners and determine their identity by quantitative mass spectrometry. We will also employ the proximity ligation assay (PLA) to study the nanoscale organisation of cytoskeletal components around the resting and activated BCR. Specifically, we will use Fab-PLA, an improved and high-resolution version of the standard PLA method, to study the proximity of BCR associated proteins in the 10-20 nm range. The identified BCR proximal cytoskeletal elements will be tested in our insect S2 cell rebuilding system for their ability to guard the BCR from the action of the BCR signal transducing kinase Syk. In our PLA studies, we have already identified several elements that are in close proximity to the resting BCR, Our overall goal is to better understand the resting state of B lymphocytes at the molecular level and how this prevents B-cell hyperactivity and autoimmunity.

Fig. 1: The resting BCR forms closed oligomers that are localised on the B cell surface in specialized protein islands with defined lipid and protein composition. A monomeric BCR that can not form an oligomer is signalling active.
Publications P 02:

Levit-Zerdoun, E., Becker, M., Pohlmeyer, R., Wilhelm, I., Maity, P.C., Rajewsky, K., Reth, M., and Hobeika, E. (2016). Survival of Igalpha-Deficient Mature B Cells Requires BAFF-R Function. J Immunol 196, 2348-2360.

Volkmann, C., Brings, N., Becker, M., Hobeika, E., Yang, J., and Reth, M. (2016). Molecular requirements of the B cell antigen receptor for sensing monovalent antigens. EMBO J pii: e201694177.

Fiala, G.J., Janowska, I., Prutek, F., Hobeika, E., Satapathy, A., Sprenger, A., Plum, T., Seidl, M., Dengjel, J., Reth, M., et al. (2015). Kidins220/ARMS binds to the B cell antigen receptor and regulates B cell development and activation. J Exp Med 212, 1693-1708.

Hobeika, E., Levit-Zerdoun, E., Anastasopoulou, V., Pohlmeyer, R., Altmeier, S., Alsadeq, A., Dobenecker, M.W., Pelanda, R., and Reth, M. (2015). CD19 and BAFF-R can signal to promote B-cell survival in the absence of Syk. EMBO J 34, 925-939. 

Maity, P.C., Blount, A., Jumaa, H., Ronneberger, O., Lillemeier, B.F., and Reth, M. (2015). B cell antigen receptors of the IgM and IgD classes are clustered in different protein islands that are altered during B cell activation. Sci Signal 8, ra93.

Ubelhart, R., Hug, E., Bach, M.P., Wossning, T., Duhren-von Minden, M., Horn, A.H., Tsiantoulas, D., Kometani, K., Kurosaki, T., Binder, C.J., Sticht, H., Nitschke, L., Reth, M., and Jumaa, H. (2015). Responsiveness of B cells is regulated by the hinge region of IgD. Nat Immunol 16, 534-543.

Hutzler, S., Ozgor, L., Naito-Matsui, Y., Klasener, K., Winkler, T.H., Reth, M., and Nitschke, L. (2014). The ligand-binding domain of Siglec-G is crucial for its selective inhibitory function on B1 cells. J Immunol 192, 5406-5414.

Klasener, K., Maity, P.C., Hobeika, E., Yang, J., and Reth, M. (2014). B cell activation involves nanoscale receptor reorganizations and inside-out signaling by Syk. Elife 3, e02069.

Fiala, G.J., Kaschek, D., Blumenthal, B., Reth, M., Timmer, J., and Schamel, W.W.A. (2013). Pre-clustering of the B cell antigen receptor demonstrated by mathematically extended electron microscopy. Front Immunol 4, 427.

Muller, J., Obermeier, I., Wohner, M., Brandl, C., Mrotzek, S., Angermuller, S., Maity, P.C., Reth, M., and Nitschke, L. (2013). CD22 ligand-binding and signaling domains reciprocally regulate B-cell Ca2+ signaling. Proc Natl Acad Sci U S A 110, 12402-12407.