Viral-like characteristics of particle aggregates in a lymphoblastic cell line

A lymphoblastic cell line (K45) established from a child with acute lymphoblastic leukemia (ALL) is characterized by a profusion of intracytoplasmic particle aggregates (PA) similar in morphology to those occurring in fresh childhood ALL cells. The PA in K45 cells were examined for morphology and capacity for nucleic acid synthesis to test the hypothesis that they are identical to those in fresh ALL cells, and also to identify characteristics which might distinguish PA from cell organelles and which might determine if they are viral-like. In contrast to cell organelles, the PA in both K45 and ALL cells were found to be characterized by a localized thickening of the particle wall. Furthermore, autoradiography of K45 cells showed uptake by PA of 3H uridine rather than 3H thymidine indicating an RNA composition. The presence of PA in profusion was associated with, but preceded necrotic death of K45 cells. These combined features suggest that the PA in K45 and in ALL cells are identical, that they are distinct from cell organelles, are not formed as a consequence of the initiation of cell death and that, while their exact nature remains unknown, a viral origin cannot be excluded.