Pre-clustering of the B cell antigen receptor demonstrated by mathematically extended electron microscopy

06.12.2013

Fiala GJ, Kaschek D, Blumenthal B, Reth M, Timmer J, Schamel WW.

Front Immunol. 2013;4:427.

Front Immunol          online article

The BIOSS Nanoscale Explorer Program (BiNEP) aims to study signalling molecules at the nanoscale level. In this BIOSS publication, we used the B cell antigen receptor (BCR) as an example, since its nano-scale organization on the B cell surface prior to antigen encounter is controversial. After fixing B cells, we stained the BCRs on the cell surface with immuno-gold and visualized the distribution of the gold particles by electron microscopy. Approximately 30% of the gold
particles were clustered. However the low staining efficiency of 15% precluded a quantitative conclusion concerning the nano-clustering state of the BCRs. To overcome this limitation, we used Monte-Carlo simulations to include or to exclude possible distributions of the BCRs. Our data suggest that 40% of the surface IgD-BCR was present in dimers and 60% formed large laminar clusters of about 18 receptors. In contrast, a transmembrane mutant of the mIgD molecule only formed IgD-BCR dimers. Our approach complements high resolution fluorescence imaging and clearly demonstrates the existence of preformed BCR nano-clusters.