Lymphocyte mechanical response triggered by cross-linking surface receptors.

Abstract

A recently developed method was used to measure changes in the deformability of lymphocytes triggered by cross-linking cell surface proteins. The study was motivated by 2 previously demonstrated phenomena: the redistribution (capping) of cross-linked surface Ig (sIg) on B lymphocytes and the inhibition of capping and lateral diffusion (anchorage modulation) of sIg by the tetravalent lectin concanavalin A (Con A). Both capping and anchorage modulation are initiated by cross-linking cell surface proteins and both require participation of the cytoskeleton. The resistance of lymphocytes to deformation strongly increased when sIg or Con A acceptors were cross-linked. Changes in deformability were measured in terms of an empirical stiffness parameter, defined as the rate at which the force of cellular compression increases with the extent of compression. For untreated cells the stiffness was .apprx. 0.15 mdyn/.mu.m; for cells treated with antibodies against sIg or with Con A the stiffness increased to .apprx. 0.6 or 0.4 mdyn/.mu.m, respectively. The stiffness decreased after completion of the capping of sIg. The increases in stiffnesses could be reversed to various extents by cytochalasin D and by colchicine. The need for cross-linking was demonstrated by the failure both of monovalent Fab'' fragments of the antibodies against sIg and of succinylated Con A (a poor cross-linker) to cause an increase in stiffness. Capping and anchorage modulation involve changes in the lymphocyte cytoskeleton and possibly other cytoplasmic properties, which increase the cellular viscoelastic resistance to deformation. Similar increases in cell stiffness could be produced by exposing cells to hypertonic medium, azide ions and to a calcium ionophore in the presence of Ca2+. These results shed new light on the capabilities of the lymphocyte cytoskeleton and its role in capping and anchorage modulation. Measurements of cellular deformability can characterize changes in cytoskeletal functions initiated by signals originating at the cell surface.