A CELL-LINE THAT CAN INDUCE THYMOCYTE POSITIVE SELECTION

THE thymus positively selects thymocytes that bear T-cell receptors which recognize antigen presented by self major histocompatibility complex (MHC) proteins1,2. positive selection is usually driven by MHC products on radiation-resistant cortical epithelial cells3-5. It is unknown whether positive selection is mediated by all thymic epithelial cells or by some specialized subsets4. Here we introduce an H-2(b)-expressing thymic epithelial cell line into the thymuses of lethally irradiated H-2k animals reconstituted with H-2b/k F1 BM or fetal liver cells. I-A(b)-restricted T cells are found in these animals, demonstrating that selection occurs on the introduced epithelial cells.