Anergic T cells exert antigen-independent inhibition of cell-cell interactions via chemokine metabolism

Abstract

Due to their ability to inhibit antigeninduced T-cell activation in vitro and in vivo, anergic T cells can be considered part of the spectrum of immunoregulatory T lymphocytes. Here we report that both murine and human anergic T cells can impair the ability of parenchymal cells (including endothelial and epithelial cells) to establish cell-cell interactions necessary to sustain leukocyte migration in vitro and tissue infiltration in vivo. The inhibition is reversible and cell-contact dependent but does not require cognate recognition of the parenchymal cells to occur. Instrumental to this effect is the increased cell surface expression and enzymatic activity of molecules such as CD26 (dipeptidyl-peptidase IV), which may act by metabolizing chemoattractants bound to the endothelial/epithelial cell surface. These results describe a previously unknown antigen-independent antiinflammatory activity by locally generated anergic T cells and define a novel mechanism for the long-known immunoregulatory properties of these cells. IntroductionT-cell anergy has been defined as a "cellular state in which a lymphocyte is alive but fails to display certain functional responses (including cell division and interleukin 2 [IL-2] production) when optimally stimulated through both its antigen-specific receptor and any other receptor that is normally required for full activation." 1 Anergic T cells can be generated in vitro and in vivo by various mechanisms, 1,2 all involving partial or inappropriate stimulation. While losing their proliferative and effector potential, anergic T cells have long been known to be able to exert immunoregulation. The potential for anergic T cells to act as suppressor cells came first from a superantigen in vivo model in which anergic T cells acted as efficient suppressor cells in an antigen-nonspecific manner. 3 More recently, murine anergic T cells either generated in vivo or rendered anergic in vitro with immobilized anti-CD3 and adoptively transferred have been shown to prolong skin allograft survival in an antigen-specific manner. 4,5 In the human system, anergic CD4 ϩ T cells were shown to exert contact-dependent and antigen-specific suppression in vitro. 6,7 The mechanism by which anergic T cells exert their immunoregulatory properties appears to be indirect by altering the antigen presenting cells (APCs) immunogenicity 8,9 in a cell-cell contactdependent manner. The molecular basis for this effect is still unknown and it has been hypothesized to involve the induction of "regulatory" molecules on the anergic T cells, capable of delivering negative signals to the APC. 2 It has recently become clear that the initial stages of T-cell activation are mediated by antigen-independent interactions, which establish areas of focal contact between T cells and APCs. 10,11 Such interactions are initiated by chemoattractant-induced cell polarization and subsequent redistribution of adhesion molecules on the T-cell surface. These, in turn, allow T-cell receptor (TCR) interactions with the major histocompatibili...

Tolerant T cells display impaired trafficking ability

“…In line with our previous observations [10], a moderate but reproducible increase in the expression of CD26 by all the clonotypic T cells (which was statistically significant in the clonotypic T cells from mice fed 100 mg of OVA, and was almost significant in the OVA o/n group) was observed in tolerizing conditions (Fig. 6C).…”

“…1D) showed that anergic T cells failed to up-regulate CD25 and CD69 as compared to activated T cells, and displayed profound down-regulation of the lymphocyte function-associated antigen (LFA)-1 integrin and failed to express the chemokine receptor CXCR4. Finally, as we have previously described [10], dipeptidyl-peptidase CD26 expression was specifically up-regulated following anergy induction. In parallel, hyporesponsive T cells (5Â10 5 -7Â10 5 /well) and controls were seeded onto female C57BL/6 endothelial cell (EC) monolayers (5Â10 4 /well) grown overnight on transwells.…”

“…We have previously reported that anergic T cells can inhibit cell-cell interactions leading to migration by metabolizing chemokines via CD26-mediated enzymatic activity [10]. As CD26 expression was up-regulated by hyporesponsive T cells, we tested whether their presence inhibited migration of resting T cells in vitro.…”

“…Resting B9 T cells (5Â10 5 /well) were seeded onto female C57BL/6 EC monolayers in the presence of an equal number of unresponsive or activated T cells, or with medium alone. In some experiments, anergic T cells were pretreated either with an anti-CD26 antibody (5 lg/ml), with an isotype-matched control antibody (5 lg/ml), or with the ectopeptidase-blocking peptide YY [pYY(3-36), 30 nM] as previously described [10]. As shown in Fig.…”

“…The functional role of dipeptidyl-peptidase activity in the nonspecific inhibition of T cell migration was then tested ex vivo as previously described [10]. Following incubation with a blocking anti-CD26 mAb, non-binding isotype-matched mAb or medium, T cells (5Â10 6 -7Â10 6 /well) from naive (Saline), primed (OVA CT) and tolerant (OVA o/n) recipients were added to EC monolayers.…”