Internalization of MHC class I molecules is a prerequisite for endocytosis of endorphin by lymphocytes0

Abstract

The nature of the inleraction between γ‐type endorphins and the HLA class I molecules was studied by immunoelectronmicroscopy. The HLA molecules were not involved in the actual binding of endorphin to the cell. In contrast, for the endocytosis of γ‐endorphin, co‐internalization of the HLA class I molecules is essential. The internalization process starts with clustering of γ‐endorphin and HLA class I molecules in coated pits. Cells that do not carry HLA class I molecules (Daudi) or do not internalize HLA class I molecules (EBV‐transformed B cells) bind but do not internalize γ‐endorphin. On the basis of these observations, we suggest that the MHC class I molecules may function as transport molecules. Whether it is a general phenomenon that non‐immunological ligands use the HLA class I molecules to get into the cell and immunological ligands (viral proteins) to reach the cell surface, remains to be established. Copyright © 1991, Wiley Blackwell. All rights reserved