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Specialized transendothelial dendritic cells mediate thymic T-cell selection against blood-borne macromolecules

ABSTRACT: T cells undergo rigorous selection in the thymus to ensure self-tolerance and prevent autoimmunity, with this process requiring innocuous self-antigens (Ags) to be presented to thymocytes. Self-Ags are either expressed by thymic stroma cells or transported to the thymus from the periphery by migratory dendritic cells (DCs); meanwhile, small blood-borne peptides can access the thymic parenchyma by diffusing across the vascular lining. Here we describe an additional pathway of thymic Ag acquisition that enables circulating antigenic macromolecules to access both murine and human thymi. This pathway depends on a subset of thymus-resident DCs, distinct from both parenchymal and circulating migratory DCs, that are positioned in immediate proximity to thymic microvessels where they extend cellular processes across the endothelial barrier into the blood stream. Transendothelial positioning of DCs depends on DC-expressed CX3CR1 and its endothelial ligand, CX3CL1, and disrupting this chemokine pathway prevents thymic acquisition of circulating proteins and compromises negative selection of Ag-reactive thymocytes. Thus, transendothelial DCs represent a mechanism by which the thymus can actively acquire blood-borne Ags to induce and maintain central tolerance. T cells are selected in the thymus, through interaction with self-antigens, to remove autoreactive cells. Here the authors show that a specialized thymic dendritic cell subset juxtaposes to microvessels, requires CX3CR1/CX3CL1 for this positioning, and has processes extruding into the blood stream to sample soluble macromolecules and assist in T cell selection.

SUBMITTER: Vollmann E

PROVIDER: S-EPMC8553756 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Specialized transendothelial dendritic cells mediate thymic T-cell selection against blood-borne macromolecules

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