Lymphocyte recognition of lymph node high endothelium. III. Enhancement by a component of thoracic duct lymph.

The first step in the entry of blood lymphocytes into lymph node is the binding of these cells to venules lined by high endothelium (HEV). This recognition event has been studied using a model system in which rat thoracic duct lymphocytes (TDL) adhere selectively to HEV when overlaid onto lymph node sections. We now report that this binding is increased by a lymph fraction designated adherence enhancing factor (AEF). Lymph depleted of cells and chylomicra was fractionated with (NH4)2SO4. Material that precipitated between 60 and 80% saturation was dissolved in buffer and extracted with chloroform/methanol; the aqueous phase was used as the source of AEF. The factor was nondialyzable, trypsin sensitive, and heat stable (70 degrees C, 30 min). Lymph node sections pretreated with AEF showed a 2- to 3-fold increase in the number of TDL bound to HEV and a 5 to 10-fold increase in the number of HEV with more than 5 adherent lymphocytes. The effect of AEF was specific: 1) No increase in lymphocyte binding to non-HEV areas of the tissue section occurred. 2) The binding of both TDL and spleen lymphoid cells to HEV was enhanced, but thymocyte attachment was not promoted. We conclude that AEF has biologic properties that might enable it to play a physiologic role in lymphocyte recirculation.