The Journal of Cell Biology, Vol 106, 697-703, Copyright © 1988 by The Rockefeller University Press
Relation between the organization of spectrin and of membrane lipids in lymphocytes
BJ Del Buono, PL Williamson and RA Schlegel
Department of Molecular and Cell Biology, Pennsylvania State University, University Park 16802.
In lymphocytes, the cytoskeletal protein spectrin exhibits two
organizational states. Because the plasma membrane lipids of lymphocytes
also display two organizational states, it was asked whether there is a
relation between the organization of spectrin and of membrane lipids. When
mouse thymocytes were stained with merocyanine 540 (MC540), a fluorescent
lipophilic probe that binds preferentially to loosely packed, disorganized
lipid bilayers, some cells fluoresced brightly and some only dimly or not
at all. When the same population was stained for spectrin by indirect
immunofluorescence, the spectrin in some cells was uniformly distributed,
while in others it was concentrated in a unipolar aggregate. Techniques
enriching for mature thymocytes selected for cells displaying low MC540
fluorescence and aggregated spectrin, the same characteristics found in
peripheral blood lymphocytes. Flow cytometric sorting of thymocytes based
on MC540 phenotype simultaneously sorted them by spectrin phenotype.
Finally, treatment with agents that alter the distribution of spectrin
caused mature lymphocytes to display high MC540 fluorescence and uniform
spectrin. Thus, a relation exists between the organizational states of
spectrin and of membrane lipids in lymphocytes: aggregated spectrin is
found in cells with tightly organized membrane lipids, uniform spectrin in
those with loosely organized lipids. Spectrin may thus be involved in
modulating membrane lipid organization in lymphocytes as it is in
erythrocytes. Since loosely organized lipids may promote adhesion of blood
cells to reticuloendothelial cells, spectrin may thereby be involved in
transducing an internally generated adhesion signal to the lymphocyte
surface.
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