Ultrastructural events in the cytoplasmic death of lethally-irradiated human lymphocytes.

Normal human peripheral-blood lymphocytes were irradiated with a dose of X-rays and processed for electron microscopic 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 hours and invagination of the inner nuclear membrane after 4 hours of irradiation. By 24 hours, the cytoplasmic and nuclear ultrastructural integrity was lost. The study suggested that, for high doses of X-radiation, the plasma membrane of the human peripheral-blood lymphocytes was the most sensitive target.