Early detection of apoptosis in defined lymphocyte populations in vivo

Recently many methods have been developed for the detection of apoptosis. However, all of them have some limitations in determining whether specific subsets of cells are undergoing apoptosis. In this paper we describe a technique in which one simultaneously stains for cell surface markers with fluorescent monoclonal antibodies and for nuclear DNA breaks using in situ DNA nick translation detectable by fluorescence. The method has been evaluated using radiation-induced programmed cell death of lymphocytes and compared with some other techniques. It was found that the method is very specific and sensitive. It enabled us to enumerate apoptotic cells at the single cell level and simultaneously determine their subset-specific surface antigen profile both in vivo and in vitro. It is also insensitive to nicks present in replicating cells. Our data suggest that this method may be useful for the study of programmed cell death of antigen specific T cells in vivo.