Display of clustered antigen by follicular dendritic cells tunes B-cell receptor activation
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To generate high-affinity antibodies against pathogens, B cells engage antigens displayed on the surface of follicular dendritic cells (FDCs) in secondary lymphoid tissues. Binding of cognate antigen by the B-cell receptor (BCR) causes Src kinase activation and phosphorylation of SYK (pSYK), serving as a platform for downstream signaling. However, how presentation of antigen by FDCs influence antigen binding and intracellular signaling in B cells remains unclear. Here, we show that antigen occurs in submicron pre-clusters on FDCs. We use nanoscale ligand patterning to present clustered antigens on tension force tethers in relevant cluster geometries in vitro. Clustering of antigens greatly increases BCR activation in a pattern-size-dependent manner, correlating to exclusion of the tyrosine phosphatase CD45 from BCR-antigen complexes. Increased height of antigen placement reduces CD45 exclusion with concomitant reduction in pSYK. Super-resolution imaging reveals reduced levels of pSYK at the edges of antigen patterns where CD45 interactions are greater, indicating a geometric control of BCR triggering.
