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An in vitro model of lymphocyte homing. II. Membrane and cytoplasmic events involved in lymphocyte adherence to specialized high-endothelial venules of lymph nodes.

Rat thoracic duct lymphocytes (TDL) are capable of selective adherence to the endothelium of high-endothelial venules (HEV) when overlaid onto glutaraldehyde-fixed sections of lymph nodes. The data presented indicate that lymphocyte adherence is an energy-dependent, calcium-requiring event that involves membrane determinants on TDL which are sensitive to trypsin. Surface sialic acids on lymphocytes are not essential and treatment of the cells with neuraminidase does not interfere with their attachment to HEV. There was no evidence that microtubule-associated functions play a role in binding. Adherence, however, is abolished by cytochalasin B, indicating that the cytoplasmic contractile microfilament system exerts an important effect. The results imply that lymphocyte surface membrane modulation is involved in the development of strong adhesive forces that bind the cells to the endothelium. In addition, lymphocyte-HEV adherence is reduced by ionophore A-23187, an agent known to inhibit surface membrane receptor movement. It is suggested that specific binding of recirculating lymphocytes to HEV is not a passive event, but that activation of cytoplasmic contractile forces in the lymphocyte is required for the formation of stable lymphocyte-HEV binding.