L cells infected with the virus of lymphocytic choriomeningitis, strain , produced infectious progeny; this was unaccompanied by visible signs of cell damage. Serial cultivation of infected cells in a medium free of antibodies was easily accomplished. Initially, retardation of cell multiplication and of first subculture cytopathic effects were observed. Later, a state of equilibrium was attained in which the cells multiplied at a normal rate, while continually producing and releasing virus. Although almost every cell of these carrier cultures could be shown by immunofluorescence to be infected, morphologically and functionally pathological alterations were not found.

After prolonged cultivation the carried virus was found to be incomplete; its ability to spread from cell to cell was greatly reduced; its ability to kill mice was abolished. These losses were not regained by passages in various hosts. Otherwise the carried virus resembled the original virus in conferring solid immunity to mice, reacting specifically with antibodies and sedimenting in the ultracentrifuge like lymphocytic choriomeningitis virus.

To characterize more fully the virus-host relationship, the following facts have been established. No antigens, alien for L cells, were found on the cell surface. Most clones from single cells carried lymphocytic choriomeningitis-specific antigen in every cell. A few clones were evidently completely free of the virus. Some cultures derived from single cells consisted of a mixed population of infected and antigen-free cells.

Homologous interference was absolute; heterologous interference against vesicular stomatitis, encephalomyocarditis and vaccinia viruses could not be demonstrated.

Treatment of L (Arm) cultures with lymphocytic choriomeningitis-neutralizing antibodies slowly decreased the proportion of antigen-containing cells. This ‘cure’ was real, and, furthermore, not caused by the inhibition of multiplication of L (Arm) cells reacting with antibodies. This observation indicated that the persistent infection of L cells with the lymphocytic choriomeningitis virus, strain , was not only maintained by a vertical transfer of virus from parent to daughter cells but that horizontal spread played a role.


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