Laminin-411 Is a Vascular Ligand for MCAM and Facilitates TH17 Cell Entry into the CNS

TH17 cells enter tissues to facilitate pathogenic autoimmune responses. Herein, they characterize MCAM (CD146) as an adhesion molecule that defines human TH17 cells. Parental CHO cells, lacking MCAM expression or CHO cells stably transfected with mouse MCAM were incubated in the presence of laminin-411 or laminin-511. They identify the MCAM ligand as laminin 411, an isoform of laminin expressed within the vascular endothelial basement membranes. hMCAM binds to a ligand in the ECM with identical staining to laminin a4. Moreover, mMCAM colocalizes with laminin 411 on the choroid plexus, and shows no specific binding to tissues from LAMA4 -/- mice. Their data suggest that MCAM and laminin-411 interact to facilitate TH17 cell entry into tissues and promote inflammation. The specific location of laminin 411 in the endothelial basement membrane may either function to augment adhesion of cells attempting CNS endothelial penetration or serve as an adhesion based gating system to signal appropriate entry mechanisms. As such, modulation of the interaction between MCAM and laminin 411 represents a novel and selective approach that may help to maintain or restore homeostasis to inflamed tissues in autoimmune diseases.