Comparison of immunologic synapse to model of new contact described by Gunzer and colleagues. The T cells (red) and B cells (green) form an immunologic synapse (A) in which the secretory apparatus (blue) and microtubule organizing center (MTOC; ^*) are positioned close to the interface, and molecule transport (arrows) is toward the interface, characterized by a ring or adhesion molecules (solid red). Both the T and B cells are relatively sessile. In a collagen gel (yellow), the same cells form a different structure in which the T cell continues to migrate (B). The migratory behavior of the T cell is consistent with maintenance of the MTOC and secretory apparatus in the uropod and the movement of the molecule linked to surface receptor away from the interface to the back of the cell (arrows). The B cell appears to attach to the leading lamellipodia and to be pushed forward. The nature of the adhesive structure is not known, but overall cytoskeletal organization is likely to be very different from an immunologic synapse.