Cytoskeletal polarity in mammalian lymphocytes in situ

The distribution of vimentin and spectrin in lymphocytes within murine lymphoid tissues was studied by means of immunofluorescence. A polarized submembranous aggregate of intermediate filaments was observed to be characteristic of lymphocytes within the medulla of the thymus as well as in lymphocytes within specific areas of spleen and lymph-node. This aggregate was determined to be in close association with a similarly polarized aggregate of spectrin. Lymphocytes of both B and T surface phenotype comprise the population of cells that are naturally polarized in terms of these cytoskeletal proteins. Lymphocytes with such a naturally polarized cytoskeleton are not observed in the spleen until approximately 5 days after birth, but are observed in the thymus by day 19 of gestation. Incubating lymphocytes with cytochalasin D, but not colchicine, caused a rapid dispersal of the spectrin aggregate without altering the polar accumulation of intermediate filaments. When splenic B-cells were allowed to form uropods as a result of ligand binding, the uropod (as well as surface receptor "cap") was positioned above the region containing the polar aggregate of spectrin and vimentin. The possible physiological significance of naturally occurring cytoskeletal polarity in lymphocytes is discussed.