Differential targeting of secretory lysosomes and recycling endosomes in mast cells revealed by patterned antigen arrays.

Polarized response towards a contact interface is a common theme in intercellular signaling. To visualize spatial regulation of stimulated secretion within a contact region, we exposed IgE-sensitized rat basophilic leukemia (RBL) mast cells to a surface that was patterned on the microm scale with hapten-containing lipid bilayers to activate cell surface IgE-receptor complexes. We find that, within 10 minutes of stimulation, fusion of individual secretory lysosomes is targeted towards the cell-substrate interface, but is spatially segregated from the patterned bilayers and receptor signaling complexes. By contrast, stimulated outward trafficking of recycling endosomes is preferentially targeted towards the patterned bilayers. High spatial resolution of both antigen presentation in these arrays and detection of exocytotic events provides direct evidence for the heterogeneity of polarized responses.