Laminin Stromal Fibers Regulate T Cell Trafficking Through Lymph Nodes During Tolerization.

Abstract

Background: CD40-CD40L costimulatory blockade plus donor-specific splenocyte transfusion (DST) result in tolerance by inducing regulatory T cells within the lymph node (LN). Laminins contain a variable α-chain, including α4 and α5, and affect lymphocyte extravasation through high endothelial venules (HEV) and migration through the LN. We hypothesized that tolerance induction requires unique LN laminin arrangements that regulate T cell trafficking through the LN. Methods: C57BL/6 mice were made tolerant or immune with BALB/c DST +/- anti-CD40L mAb, and/or received BALB/c vascularized cardiac allografts. Quantitative immunohistochemistry of LN was used to define high endothelial venules (HEV), laminins, ER-TR7+ stromal fibers, Foxp3, alloantigen (YAe), and plasmacytoid dendritic cells (pDC). CD4+ T cells were migrated to CCL21 across transwell membrane inserts or laminar flow channels coated with laminin α4 and/or α5, and with MS-1 vascular endothelial cells grown to confluence. Results: Tolerance increased the ratio of laminin α4 to laminin α5 around the HEV. In contrast, immunity was associated with a relative increase in laminin α5. Laminin α4 enhanced CD4 T cell migration, causing increased track length, velocity, and adherence of lymphocytes. In contrast, laminin α5 impaired migration. Blocking the integrin binding site of laminin α5 resulted in increased numbers of tolerance-inducing pDC surrounding the HEV and prolongation of graft survival. Blocking the integrin binding site of laminin α4 resulted in a decrease in Treg and pDC surrounding the HEV, and allograft inflammation and rejection. Conclusions: Tolerance and immunity result in distinct laminin α-chain ratios, with laminin α4 being pro-tolerogenic. Laminins affect lymphocyte migration within the LN. These findings suggest tolerance induction results in LN laminin remodeling creating an environment for tolerization.