Predominant role of alpha 4-integrins for distinct steps of lymphoma metastasis.

To analyze the role of alpha4-integrins in lymphoma metastasis, sublines of the T-cell lymphoma LB were generated by retrovirus-mediated gene transfer that differ exclusively in the expression of alpha4-integrins. Using LB-alpha4 and control LB-NTK cells, we demonstrate that expression of alpha4-integrins strongly suppresses metastasis formation of LB lymphoma cells in secondary lymphoid organs such as spleen, mesenteric and peripheral lymph nodes, or Peyer's patches after i.v. injection into syngeneic BALB/c mice. Moreover, alpha4-integrin expression inhibited development of metastatic tumors in liver, lung, and kidney. Expansion of LB lymphoma cells in bone marrow was not affected by alpha4-integrin expression. In vivo migration assays using 51Cr-labeled lymphoma cells demonstrated that low-metastatic LB-alpha4 cells accumulated with the same efficiency as high-metastatic LB-NTK cells in all target organs examined and were even enriched in mucosal lymphoid organs. Collectively, these results indicate that alpha4-integrins inhibit metastasis formation of lymphoma cells at a stage subsequent to the invasion of target organs.

Crucial role of 55-kilodalton TNF receptor in TNF-induced adhesion molecule expression and leukocyte organ infiltration.

Stimulation of leukocyte adhesion to the endothelium by TNF is mediated by the up-regulation of adhesion molecules on the endothelial cell surface. C57BL/6 mice and syngenic 55-kDa TNF receptor-deficient mice (TNFRp55-/- mice) were challenged with TNF, and the kinetics of intracellular adhesion molecule-1, ICAM-1, mucosal addressin cell adhesion molecule-1, vascular adhesion molecule-1 (VCAM-1), and E-selectin expression were examined in various organs. TNF induced sustained VCAM-1 expression within 4 h in lung, liver, and kidney. In the lungs, but not in other organs, transient E-selectin expression was induced by TNF within 0.5 h and peaked at 4 h. The TNF-induced expression of VCAM-1 and E-selectin was found to be exclusively controlled by the 55-kDa TNF-receptor (TNFRp55) as demonstrated by analysis of TNFRp55-/- mice. Furthermore, TNF triggered mononuclear cell and neutrophil infiltration of lung, liver, and kidney in C57BL/6 mice but not TNFRp55-/- mice. Interestingly, MAdCAM-1 expression in the marginal sinus of the spleen was detected in wild-type mice but was absent in TNFRp55-/- mice. Together, the data suggest that in vivo the 55-kDa TNF receptor mediates the induction of VCAM-1 and E-selectin expression and is critically involved in the control of leukocyte organ infiltration.

Distinct binding specificities of integrins alpha 4 beta 7 (LPAM-1), alpha 4 beta 1 (VLA-4), and alpha IEL beta 7.

Integrin receptors are important for regulating lymphocyte recirculation and recruitment to sites of inflammation. Transfectants of the B cell lymphoma 38C13 were generated that differ exclusively in the expression of integrin beta 1 or beta 7 subunits allowing for a functional comparison of lymphocyte Peyer's patch HEV adhesion molecule 1 (LPAM-1) (alpha 4 beta 7) and very late antigen 4 (VLA-4) (alpha 4 beta 1) in an identical cellular environment. Whereas 38-beta 7 transfectants bound to purified and cellular mucosal addressin cell adhesion molecule (MAdCAM-1), unstimulated 38-beta 1 cells failed to bind MAdCAM-1. Treatment of 38-beta 1 cells with Mn2+ but not with PMA induced low level binding to MAdCAM-1. MAdCAM-1 adhesion of 38-beta 7 cells was constitutive and not enhanced by Mn2+ treatment. Similarly, MAdCAM-1-dependent adhesion to mucosal high endothelial venules was shown for 38-beta 7 but not for 38-beta 1 cells. The results therefore establish the LPAM-1-MAdCAM-1 interaction as the functionally dominant adhesion pathway for regulating lymphocyte homing to mucosal sites. Nonetheless, the activated VLA-4 on some lymphocytes may be involved in MAdCAM-1 recognition or promote binding to MAdCAM-1 in other tissues. By contrast, 38-beta 7 and 38-beta 1 transfectants did not differ in their binding capacity for vascular cell adhesion molecule 1 (VCAM-1) or fibronectin and LPAM-1 did not display any preference for interacting with either MAdCAM-1 or VCAM-1. LPAM-1 may therefore contribute significantly to cellular functions previously attributed to VLA-4. Interestingly, functional analysis of the intraepithelial lymphocyte integrin alpha IEL beta 7 which is structurally related to LPAM-1 did not reveal detectable binding activity for MAdCAM-1, VCAM-1, or fibronectin.