NONCLASSICAL BEHAVIOR OF THE MOUSE CD1 CLASS I-LIKE MOLECULE

The mouse CD1 (mCD1) molecule is a class I-like molecule that is encod ed outside of the MHC. We show here that mCD1 shares several propertie s with Ag-presenting class I molecules, including a requirement for be ta(2)-microglobulin for stable cell-surface expression in T lymphocyte transfectants and thymocytes. mCD1 is also capable of binding to mous e CD8 alpha beta heterodimers participating in the activation of CD8() T cells in a manner similar to classical class I molecules. However, mCD1 surface expression is not decreased at high temperatures in cell s that lack the transporter associated with Ag processing (TAP), inclu ding both RMA-S and Drosophila melanogaster cells. The data indicate t hat mCD1 does not require TAP to be expressed in a stable fashion at t he cell surface. We speculate that the ability of mCD1 to reach the ce ll surface in transporter-deficient cells may reflect its ability to p resent a distinct set of ligands. The properties of mCD1 described her e can account, in part, for the selection of the diverse populations o f T cells that are known to be mCD1 reactive.