epithelial cell of thymus thymic nurse cell 2022-02-18T12:43:20Z A large epithelial cell found in the thymus. This cell type may internalize thymocytes through extensions of plasma membrane. The cell surface and cytoplasmic vacuoles of a thymic nurse cell express MHC Class I and MHC Class II antigens. The interaction of these antigens with a developing thymocyte determines whether the thymocyte undergoes positive or negative selection.