Ultrastructural Events in the Cytoplasmic Death of Lethally-irradiated Human Lymphocytes

Abstract

Normal human peripheral-blood lymphocytes were irradiated with a dose of X-rays and processed for EM examination at different times after irradiation. A localized protrusion of the plasma membrane of the irradiated lymphocytes was observed in samples fixed as early as 15 min after irradiation, suggesting that the injury to the plasma membrane could have occurred during or immediately after irradiation. This was followed by fenestration of the plasma membrane, rarefaction of the cytoplasm and accumulation of cytoplasmic organelles in the centrosphere region. Localized distention of the outer nuclear envelope occurred after 2 h and invagination of the inner nuclear membrane after 4 h of irradiation. By 24 h, the cytoplasmic and nuclear ultrastructural integrity was lost. For high doses of X-radiation, the plasma membrane of the human peripheral-blood lymphocytes is probably the most sensitive target.