RESUMO
Astrocyte cultures of adult human brain were used to study the morphogenesis of measles virus at different multiplicity of infection. High-dose (1 to 10 TCD50/ml) inoculation of the culture was found to give rise to an acute infection with cytolysis on days 10-12 postinfection and formation of extracellular mature virions. Low multiplicity of infection (0.01-0.1 TCD50/ml) caused the persistence of virus. During a persistent infection the virus in titers 1.7 to 2.4 lg TCD50/ml was detected as long as up to the 3rd passage. Ultrastructural studies of such cultures revealed some features which were not observed in an acute infection: (1) the diameter of intracytoplasmic RNP increased by 1.5 times vs. that in other cell cultures because of coarse thickening of the envelope; (2) numerous immature virions in which nucleocapsids were completely or partially absent; and (3) uncommonly low number of mature virions. Moreover, alterations in the spatial orientation of cytoskeleton components, such as intermediate and thin (actin) filaments were observed. A conclusion is made that astrocytes as a reservoir for measles virus accumulation serve as the source of immature envelope virus production, which may be one of the possible causes of sclerosing panencephalitis. The causes of disturbances in RNP transport from the site of assembly to cell membrane are discussed.
