Plasma membrane topography governs the three-dimensional dynamic localization of IgM B cell receptor clusters

B lymphocytes recognize bacterial or viral antigens via different classes of the B cell antigen receptor (BCR). Protrusive structures termed microvilli cover lymphocyte surfaces and are thought to perform sensory functions in screening antigen-bearing surfaces. Here, we have studied the cell surface features of Ramos B cells and the spatiotemporal organization of the IgM-BCR using lattice light sheet microscopy in combination with tailored custom-built 4D image analysis. Ramos B cell surfaces were found to form dynamic networks of elevated ridges bridging individual microvilli. A proportion of membrane-localized IgM-BCR was found in clusters, which were associated with the ridges and the microvilli. The dynamic ridge network organization and the IgM-BCR cluster mobility were linked and both were controlled by Arp2/3 complex activity. Our results suggest that topographical features of the cell surface govern the distribution and dynamic localization of IgM-BCR clusters to facilitate antigen screening.