| Abstract: | Two morphologically distinct types of oncornavirus particles were observed in guinea pig cells. In tissues of leukemic guinea pigs, intracisternal A-type particles 90–100-nm diameter, predominated. Extracellular particles with dense core, approximately 90–110 nm in diameter, were seen only occasionally at the intercellular space of the tissues, but were predominant in plasma and sera of the same animals. Placental and fetal tissues obtained from normal guinea pigs showed only intracisternal A-type particles. Cultured guinea pig cells when treated with BrdU revealed many intracytoplasmic A-type particles 90–100-nm diameter. Budding of these A-type particles at the cell membrane to form extracellular enveloped A-type particles was observed. Extracellular virus particles with dense cores, 110–120 nm in diameter, similar to those seen in tissues and plasma of leukemic guinea pigs, were abundant in the BrdU-treated cultures. The morphology and distribution of the intracellular and extracellular virus particles in tissues and tissue cultures derived from leukemic and normal guinea pigs are compared, and the relationships between these virus particles are discussed. |
