Morphological features of apoptosis in hematopoietic cells belonging to the T-lymphoid and myeloid lineages

Taking into account that apoptosis plays a pivotal role in shaping normal h ematopoiesis, morphological features of apoptosis were investigated in both primary cells and continuous cell lines committed towards the T-lymphoid a nd the myeloid lineages. Apoptosis was induced using: dexamethasone (10(-7) M) for primary rat thymocytes; infection with the T-lymphotropic human her pesvirus 7 (HHV-7) for peripheral blood CD4+ T-cells; staurosporine (1 mu M ) for MOLT4 CD4+ lymphoblastoid T-cells, HL60 human promyelocytic and U937 human monoblastoid cells; and using senescence of the culture for primary h uman megakaryocytes. Cell morphology was examined by both transmission elec tron microscopy and in situ nick translation (NT) revealed by laser scannin g confocal microscopy. In spite of the use of different apoptotic agonists, the morphological aspects of apoptosis were similar within the T-lymphoid and the myeloid lineage. While chromatin condensation characterized the ear ly apoptotic events in both lineages, late apoptoses were mainly characteri zed by further nuclear condensation in lymphoid cells and by production of micronuclei in myeloid cells. Moreover, NT analysis clearly showed that the micronuclei derived from HL60 undergoing apoptosis were composed of both d egraded and intact DNA. Thus, T-lymphocytes and myeloid cells showed a line age-related behavior characterizing the late morphological aspects of apopt osis.