Morphological and Virological Investigations on Cultured Burkitt Tumor Lymphoblasts (Strain Raji)<xref ref-type="fn" rid="FN2">2</xref>

Cells of the Raji strain, established in vitro in Nigeria from a Burkitt lymphoma, were maintained and studied between the 16th and 28th months of culture. As judged by their mode of growth in suspension, appearance when stained, and fine structural organization, the cells were undifferentiated lymphoblasts similar to those of other tissue culture strains from Burkitt tumors. Characteristics suggesting a lack of differentiation were the formation of large aggregations containing many hundreds of individuals, a relatively large diameter, irregularly indented nuclei, and a fairly extensive cytoplasm with free ribosomes tending to clump. No virus particles could be found in the cells by electron microscopy, despite intensive searching of 16 separate samples. Although the cells were resistant to vesicular stomatitis virus, this resistance could not be transferred to other normally susceptible test cultures and an interferon-like inhibitor could not be found. The Raji cells could, however, produce interferon when stimulated by Newcastle disease virus. Unlike other cultured Burkitt tumor cells, Raji cells did not respond positively in immunofluorescence tests. The failure to detect virus particles or indirect evidence of virus infection in Raji cells is discussed.