BCR clustering reflects type of BCR signaling in DLBCL lines. (A) Superresolution microscopy of BCR units, labeled by knock-in of CD79A-GFP fusion, in live cells imaged at the point of contact with glass coverslip chamber slides (bars represent 5 µm). Red CellMask dye marks the surface membrane. BCR units are clustered in the ABC-DLBCL line HBL-1, but diffusely distributed in the GCB-DLBCL line SUDHL-4. (B) SRM of BCR units in HBL-1 cells with CD79A-GFP fusion and dual HVR replacement. The BCR with endogenous HVRs remains clustered but is diffusely distributed when replaced with TTox-reactive HVRs.