Detection of Replicating C-Type Viruses in Continuous Cell Cultures Established From Cows With Leukemia: Effect of the Culture Medium

Summary

Four long-term suspension cultures, initiated from thoracicduct or buffy-coat lymphocytes of cows with leukemia, were transferred from their regular medium [McCoy's SA medium supplemented with 20% heat-inactivated horse serum (M20HSI)] to Eagle's minimal essential medium supplemented with 20% heat-inactivated fetal calf serum (E20FSI). C-type particles were readily and consistently detected in 3 of the 4 cell lines. Mature and immature particles occurred extracellularly and within cytoplasmic vacuoles. Characteristic budding forms provided evidence for the replication and thus the viral nature of the particles. Cylindrical or tubular buds were also observed. Addition of phytohemagglutinin (PHA) to the E20FSI medium enhanced virus production in only 1 of these VLP-positive cell lines. Subsequent and more extensive examinations of 2 VLP-positive cell lines, grown in M20HSI, revealed replicating C-type virus, sbut consisderably fewer than observed when these cell lines were grown in E20FSI. The relationship of these particles to those observed in short-term, bovine buffy-coat cultures treated with PHA, as well as their possible significance in the etiology of bovine leukemia, remains to be determined.