Interaction of α4-integrin with VCAM-1 is involved in adhesion of encephalitogenic T cell blasts to brain endothelium but not in their transendothelial migration in vitro
Introduction
Under physiological conditions, lymphocyte traffic into the healthy central nervous system (CNS) is very low. The endothelial blood–brain barrier (BBB), which inhibits the free exchange of molecules between the blood and the CNS, also tightly controls lymphocyte entry into the CNS. However, in inflammatory diseases of the CNS such as multiple sclerosis (MS) or in the animal model experimental autoimmune encephalomyelitis (EAE) circulating cells readily get access to the CNS. In EAE autoaggressive T cells are activated outside the CNS and have to gain access to the CNS in order to start the molecular events leading to inflammation, edema and demyelination. The interaction of encephalitogenic T cells with the BBB endothelium therefore is a critical step in the pathogenesis of EAE. In general, lymphocyte/endothelial interaction is regulated by the sequential interaction of different adhesion or signaling molecules on lymphocytes and on endothelial cells (Butcher, 1991; Springer, 1994). Based on the observation that monoclonal antibodies (mAbs) directed against α4-integrin or VCAM-1 inhibit the development of EAE in several models, it has been concluded that α4β1 mediated interaction with VCAM-1 on the BBB endothelium plays a critical role in the recruitment of inflammatory cells across the BBB (Yednock et al., 1992; Baron et al., 1993; Kent et al., 1995). A role for α4β7 which is another ligand for VCAM-1 (Ruegg et al., 1992) was not considered in these studies. Recently we could show that several antibodies directed against α4-integrin and also a panel of antibodies directed against endothelial VCAM-1 successfully inhibited the development of clinical EAE whereas antibodies directed against β7-integrin or against the α4β7-heterodimer did not interfere with the disease course, implying that α4β7-integrin is not necessarily involved in inflammatory cell recruitment across the BBB (Engelhardt et al., 1998a). Taken together, these data now provide good evidence that α4β1-integrin and VCAM-1 are required for the continuous entry of inflammatory cells across the inflamed BBB during EAE. However, it remains to be investigated, if α4-integrin mediated interaction with endothelial VCAM-1 can be involved in the initial recruitment of encephalitogenic T cell blasts across the healthy BBB into the CNS parenchyme. In order to address this, we investigated the interaction of freshly activated encephalitogenic T cell blasts with brain endothelium in vitro. We focused on defining the involvement of α4β1- and α4β7-mediated interaction with endothelial VCAM-1 in T cell adhesion and transendothelial migration.
Section snippets
mAbs
The hybridomas M1/9 (anti-CD45), MK2.7 (anti-VCAM-1, rat IgG1), FD441.8 (anti-LFA-1, rat IgG2a), PS/2 (anti-α4-integrin, rat IgG2b), Fib 30 (anti-β7-integrin, rat IgG2a), Fib 504 (anti-β7-integrin, rat IgG2a), DATK 32 (anti-α4β7-integrin, rat IgG2a), MJ7/18 (anti-endoglin, rat IgG2a, used as a binding, non-blocking antibody-control, Ge and Butcher, 1994) and Hermes (anti-human-CD44 used as an irrelevant antibody-control, rat IgG2a) were purchased from American Type Culture Collection (ATCC;
α4β1 and α4β7 are both expressed on encephalitogenic and non-encephalitogenic T cell lines
We established a panel of T cell lines specific for the encephalitogenic peptide amino acids 139–151 of protein lipid protein (PLP) from SJL/N mice. Here, three representative lines are described in greater detail. All established T cell lines were CD4+ CD8− Thelper 1 cells which recognize their specific antigen in the molecular context of MHC class II (data not shown). Intravenous injection of freshly activated T cell blasts of the T cell lines SJL.PLP7 or SJL.PLP9 into healthy syngeneic naive
Discussion
In the meantime, several in vivo studies have demonstrated that monoclonal antibodies directed against α4-integrin and VCAM-1 interfere with the development of EAE (Yednock et al., 1992; Baron et al., 1993; Engelhardt et al., 1998a). The therapeutic efficacy has been attributed to the inhibition of α4β1/VCAM-1 mediated recruitment of inflammatory cells across the endothelial BBB as the cellular infiltrates in the CNS are reduced to absent in these animals. This has been substantiated by the
Acknowledgements
We thank Gabriele Hoch and Martina Schulz for expert technical assistance. Urban Deutsch und Yvonne Reiss are gratefully acknowledged for critically discussing the manuscript. We also wish to express our thanks to the reviewers whose comments grealty helped to improve our manuscript.
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