DENDRITIC CELLS ACQUIRE ANTIGEN FROM APOPTOTIC CELLS AND INDUCE CLASS-I RESTRICTED CTLS

CD8(+) cytotoxic T lymphocytes (CTLs) mediate resistance to infectious agents and tumours. Classically, CTLs recognize antigens that are loc alized in the cytoplasm of target cells, processed and presented as pe ptide complexes with class I molecules of the major histocompatibility complex (MHC)(1). However, there is evidence for an exogenous pathway whereby antigens that are not expected to gain access to the cytoplas m are presented on MHC class I molecules(2-6). The most dramatic examp le is the in vivo phenomenon of cross-priming(7): antigens from donor cells are acquired by bone-marrow-derived host antigen-presenting cell s (APCs) and presented on MHC class I molecules. Two unanswered questi ons concern the identity of this bone-marrow-derived cell and how such antigens are acquired. Here we show that human dendritic cells, but n ot macrophages, efficiently present antigen derived from apoptotic cel ls, stimulating class I-restricted CD8(+) CTLs, Our findings suggest a mechanism by which potent APCs acquire antigens from tumours, transpl ants, infected cells, or even self-tissue, for stimulation or toleriza tion of CTLs.