HEAT-SHOCK PROTEIN EXPRESSION ON THE MEMBRANE OF T-CELLS UNDERGOING APOPTOSIS

Heat-shock proteins (hsp) represent a highly conserved family of prote ins, normally localized in the cytoplasm and nucleus, whose expression is induced in situations involving cell stress. This paper reports th e unusual translocation of hsp to the cell membrane of T cells undergo ing apoptosis. We observed that glucocorticosteroid-induced thymocyte death is associated to the surface expression of hsp 60 and hsp 70 in a discrete fraction of apoptotic cells. hsp surface expression is clos ely related to a thymic subset of immature CD3(low/-) T cells. The exp ression of surface hsp 60 appears early after treatment with dexametha sone (3 hr) whereas the membrane expression of hsp 70 follows differen t kinetics and peaks later. Morphological analysis of the hsp(+) apopt otic cells suggest that this subset represents late-stage apoptotic ce lls at their minimal volume before fragmentation into apoptotic bodies . Membrane expression of hsp is also associated with apoptosis in peri pheral blood mononuclear cells from AIDS patients cultured in vitro. A ltogether, we show that a discrete fraction of cells undergoing apopto sis expresses membrane hsp 60 and hsp 70, supporting the hypothesis th at apoptosis causes a radical alteration in the expression of cell sur face molecules. Surface hsp expressed during apoptosis may constitute a novel immune-context able to generate packages of self- and exogenou s antigens, originating from degradation of altered cells.