Cytoplasmic Fibrils in Mixed Lymphocyte Cultures

Bundles of cytoplasmic fibrils are described in activated (increased cytoplasm and organelles) lymphocytes and blasts in human mixed lymphocyte cultures. Similar bundles were not observed in the transformed lymphocytes in PHA cultures. They were encountered in the activated lymphocytes in the control cultures, but with a lower incidence. The fibrils were usually perinuclear, were frequently in contact with the nuclear envelopes and occasionally penetrated through defects in the nuclear membrane into the nucleus. A less frequent and less convincing connection with mitochondria was also observed.

These morphologic observations seem to indicate that the transformed cells observed in mixed lymphocyte and PHA cultures are not identical.