Abstract
The adhesion of lymphocytes to endothelial cells lining the postcapillary high endothelial venules (HEV) is the first step in their emigration from the bloodstream into lymph nodes and Peyer's patches (PP). We have recently shown that the adhesiveness of cultured rat lymph node and PP HEV cells for thoracic duct lymphocytes can be increased significantly by pretreatment with TNF-alpha, IFN-gamma, and IL-4. In the present study we investigated the role of transforming growth factor-beta 1 (TGF-beta) on the adhesiveness of nonstimulated and cytokine-stimulated PP HEV cells for rat lymphocytes. The results indicated that at picomolar concentrations, TGF-beta significantly (p less than 0.001) decreased the ability of PP HEV cells to adhere 51Cr-labeled rat lymphocytes. Maximal inhibition was observed with a TGF-beta dose of 0.5 ng/ml and an incubation time of 6 to 12 h. TGF-beta did not affect the morphology of HEV cells and had no adverse effect on their viability. Moreover, the decrease in HEV adhesiveness by TGF-beta was reversible, with lymphocyte binding returning to control level 24 h after removal of the cytokine. The specificity of TGF-beta was confirmed by the ability of neutralizing anti-TGF-beta 1 antibody, but not control serum, to abolish the inhibitory properties of the cytokine. In addition, TGF-beta completely abrogated the increased adhesiveness of PP HEV cells normally induced by TNF-alpha or IFN-gamma. In contrast, TGF-beta had no effect on the stimulating effects of IL-4. Moreover, preincubation of PP HEV cells with TGF-beta did not alter the ability of these cells to respond to IL-4. Importantly, the adhesion of rat lymphocytes to IL-4-stimulated PP HEV cells can be blocked by pretreatment of lymphocytes with the PP-homing receptor-specific 1B.2.6 antibody whereas pretreatment of human mononuclear cells with anti-very late activation antigen-4 alpha antibody inhibited only partially the binding of these cells to the IL-4-stimulated PP HEV monolayers. Taken together, these findings strongly suggest that TGF-beta and IL-4 play important regulatory roles in lymphocyte-HEV adhesion and that the stimulatory effect of IL-4 is mediated at least in part through the increased expression of organ-specific ligands on HEV cells.
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