Myosin II drives the clustering of MHC vesicles (green) and endocytotic vesicles (red) containing antigen (blue) in B cells.
Vesicles containing endocytosed antigen and those containing MHC class II molecules come together in the cell to form specialized antigen-processing lysosomes. To investigate the mechanics of this union, Vascotto and colleagues followed events in real time by live cell microscopy.
They were surprised to see that B cells contracted soon after activation with antigen. This contraction was coupled with a clustering of MHC class II toward the center of the cell, where immunofluorescence revealed that antigen vesicles also cluster.
Cell contraction relies in part on myosin II activation. Antigen stimulation of B cells led to myosin II activation. Inhibiting myosin II blocked the cell contraction,...
