THE ORIGIN AND FATE OF BETA-2M-FREE MHC CLASS-I MOLECULES INDUCED ON ACTIVATED T-CELLS

We report here that the expression of major histocompatibility complex (MHC) class I heavy chains not associated with β2-microglobulin is induced on resting human T cells by a variety of stimuli. These β2m-free class I heavy chains are not transported as such from the endoplasmic reticulum but originate from surface β2m-associated MHC class I molecules. β2m-free class I heavy chains are spontaneously released from the surface of activated cells. Cross-linking of β2mfree class I heavy chains with specific monoclonal antibodies results in the rapid down-regulation and internalization of these molecules. In contrast, β2m-associated MHC class I molecules display a different pattern of modulation. Previously, we reported that β2m-free class I heavy chains interact with CD8 molecules expressed on the same activated T cells. We propose that interactions between these molecules are involved in a mechanism regulating the function of activated T cells. © 1992.