Involvement of laminin and its receptor in abrogation of heart graft rejection by autoreactive T cells from Trypanosoma cruzi-infected mice.

Extracellular matrix ligands and receptors have been identified as determining in vivo lymphocyte positioning and activation, including effector functions in alloreactive responses. Herein we evaluated the involvement of laminin and its receptor, the very late antigen 6 (VLA-6) integrin, in CD4+ T cell-dependent autoreactivity, using a transplantation model for the autoimmune myocarditis occurring in mice chronically infected with Trypanosoma cruzi. Previous work showed that syngeneic mouse hearts grafted in the ears of chronic chagasic recipients were rejected through a CD4+ T cell-dependent mechanism. Rejection also occurred when cells from chagasic animals were transferred adjacent to hearts transplanted into naive recipients. Here, we observed the formation of a thick laminin network during rejection, with donor-derived CD4+ T cells concentrated in the laminin-rich areas. Most importantly, anti-laminin as well as anti-laminin receptor Ab inhibited the rejection of syngeneic hearts by T cells from chagasic animals. Our results suggest that interaction of the VLA-6 molecule with laminin is involved in triggering the antimyocardial autoreactive process by driving the influx of CD4+ T cells to the heart. They also support the concept that an Ag-specific T cell response, even an autoreactive one, can be modulated by in vivo interactions involving extracellular matrix ligands and receptors. In this regard, our study represents, to our knowledge, the first in vivo evidence for laminin-mediated T cell echotaxis, with simultaneous experimental demonstration of ligand and receptor involvement. Lastly, our findings indicate that treatment with anti-VLA-6 Abs can be effective in suppressing autoimmune disease activity.