ENDOCYTOSIS OF THE TCR/CD3 COMPLEX AND THE CLASS-I MAJOR HISTOCOMPATIBILITY COMPLEX IN A HUMAN T-CELL LINE

We investigated the expression of the T cell receptor (TCR)/CD3 complex on a CD4-positive human T cell lymphoma cell line treated with phorbol myristate acetate (PMA) and/or Ca2+ ionophore using fluorescence flow cytometry and fluorescence microscopic analysis. PMA induced a significant decrease in the expression of the CD3 complex on the cell membranes. Fluorescence microscopy confirmed that the down regulation is due to internalization of the antigens. Ca2+ ionophore treatment had no effect on the internalization of the CD3 complex. Double staining revealed that the vesicles containing the internalized CD3 complex and those containing intracytoplasmic class I major histocompatibility complex antigen had similar distribution in the PMA-stimulated cells, implying coexistence of these two antigens in a cytoplasmic perinuclear distribution. © 1991.