The production of a temperature-sensitive persistent measles virus infection.

A persistent infection of measles virus was established in HEp2 cells. All cells contained virus antigen when tested by specific immunofluorescence and approx. 50% were positive by haemadsorption. Infectious virus released into the supernatant medium was usually equivalent to no more than 0-001 p.f.u./cell, but between 10 and 40% of the infected cells produced plaques when plated on Vero cells. Passage of persistently infected cultures in the presence of measles antibody had no effect on the proportion of antigen-positive cells. Virus obtained from the supernatant medium of persistently infected cultures was temperature sensitive at 39-5 degrees C when tested on Vero cells whereas the original non-persistent virus produced infections on Vero cells at 39-8 degrees C. On passage of the persistently infected culture at 39-5 degrees C most of the surface antigens disappeared within 24 h whereas the intracellular virus antigens had not totally disappeared until the 5th passage.