Rapid decrease in lymphocyte adherence to high endothelial venules in lymph nodes deprived of afferent lymphatic vessels

Abstract

Occlusion of the afferent lymph flow to the lymph node (LN) results in both flattening of the endothelium of high endothelial venules (HEV) and a severe decrease in numbers of lymphocytes in transit across the walls of the flattened HEV. In the present study we have used the in vitro lymphocyte-binding assay to investigate the ability of HEV in rat LN to bind lymphocytes at various time points after occlusion of the afferent lymph flow. In addition the specificity of T and B lymphocyte adherence to HEV of such operated LN was studied. In normal LN, lymphocytes adhered to virtually all HEV using the in vitro binding assay. However, 1 and 2 weeks after operation lymphocytes bound to only 50-60% of the HEV and by 3-6 weeks 20-30%. The total numbers of lymphocytes bound to these HEV had also diminished to 10% of the control value 3-6 weeks after operation. Morphometric analysis showed that this was not only due to a reduction in the area of HEV endothelium available for lymphocyte adherence by flattening of the high endothelial cells, but also to a strong decrease in the numbers of bound lymphocytes per unit area high endothelium. In spite of the reduction in numbers of adhering lymphocytes the T/B cell ratio did not change. The results show that the reduction in lymphocyte binding of HEV in operated LN is a rapid event, probably due to loss of high endothelial cell determinants involved in binding of lymphocytes. The decrease in lymphocyte binding clearly precedes flattening of HEV endothelium suggesting that the height of high endothelial cells is of secondary importance to lymphocyte adherence.