αL-Integrin I domain cyclic peptide antagonist selectively inhibits T cell adhesion to pancreatic islet microvascular endothelium

Insulitis is a hallmark feature of autoimmune diabetes that ultimately results in islet β-cell destruction. We examined integrin requirements and specific inhibition of integrin structure in T cell and monocyte adhesion to pancreatic islet endothelium. Examination of cell surface integrin expression on WEHI 7.1 T cells revealed prominent expression of β-, β1-, αL-integrins, and low expression of αM-integrins; whereas WEHI 274.1 monocytes showed significant staining for β2-, β1-, αM-molecules and no expression of αL-molecules. Unstimulated islet endothelium showed constitutive levels of ICAM-1 counter-ligand expression with minimal VCAM-1 expression; however, TNF-α stimulation increased cell surface density of both molecules. TNF-α increased T cell and monocyte rolling and adhesion under hydrodynamic flow conditions. Administration of a cyclic peptide competitor for the αL-integrin I domain binding sites (cyclo1,12-PenITDGEATDSGC) blocked T cell adhesion without inhibiting monocyte adhesion. Examination of T cell rolling revealed that cLAB.L treatment increased the average rolling velocity on activated endothelium and significantly decreased the fraction of T cells rolling at ≤50 μm/s, suggesting that cLAB.L treatment interferes with signal activation events required for the conversion of T cell rolling to firm adhesion. These data demonstrate for the first time that cyclic peptide antagonists against αL-integrin I domain attenuate T cell recruitment to islet endothelium.

Lymphocyte transfer in streptozotocin-induced diabetes: adhesion of donor cells to islet endothelium

The interaction between intravenously transferred lymphocytes derived from spleens of multiple low-dose streptozotocin-diabetic mice with islet, exocrine pancreatic, and gastric mucosal endothelium of nondiabetic recipient mice was investigated by in vivo microscopy. Donor lymphocytes were stained with acridine red in vitro. The adoptive transfer of these cells from diabetic donor animals resulted in significantly increased lymphocyte rolling (4.46 ± 1.32%, P < 0.05) and adhesion (3.86 ± 1.04%, P < 0.05) in islets of nondiabetic recipients that had been pretreated with a single subdiabetogenic dose of streptozotocin. No increased endothelial interaction was noted in nonpretreated recipients or in experiments with nondiabetic donors. Rolling (1.19 ± 0.61 to 2.71 ± 0.62%) and adhesion (0.61 ± 0.33 to 2.80 ± 0.97%) of donor lymphocytes were low in exocrine pancreatic and gastric mucosal control tissue. It is concluded that, in this animal model, lymphocytes from diabetic donors interact preferentially with recipient islet endothelium. However, additional stimulation of recipient islet endothelium by exogenous factors is necessary to enable transferred cells to adhere to pancreatic islets.