Two types of interphase death of lymphocytes exposed to temperatures of 37--45 degrees C.

Abstract

Normal human blood lymphocytes in RPMI 1640 media with 20% human serum (pH 7.6) were exposed to temperatures of 37 to 45/sup 0/C. The processes of cell death were studied by phase contrast and electron microscopy, by time-lapse cinemicrography, and by serial counts of viable and dead cells. Dead cells showed two distinctive morphologic types: cells with pyknotic nuclei and condensed cells. Examination by phase microscopy revealed that dead cells with pyknotic nuclei had uniformly dark nuclei which were either ring-shaped, crescentic, or round; a moderate amount of clear cytoplasm; and a thin plasma membrane. When examined by electron microscopy, the pyknotic nucleus was seen as a homogenous mass of electron-dense granules without a normal architectural pattern or nuclear membrane. Electron microscopy showed the condensed cell characterized by electron-opaque cytoplasm, a dense nucleus with normal architectural features, and multiple cytoplasmic vacuoles. Serial counts of viable and dead cells showed that exposure of lymphocytes to 43 or 45/sup 0/C killed cells primarily by the process resulting in condensed cells; at 37, 41, and 42/sup 0/C, lymphocytes died primarily by pyknosis. The findings support the hypothesis that different mechanisms killed the cells above and below the critical temperature of 43/sup 0/C.