Mumps virus produced a carrier state in human conjunctiva cells that was maintained for more than 100 subcultures over a period of 3 years. Antiserum in the medium was not required. The virus had little apparent effect on the cells which grew at a rate similar to uninfected control cells. Mumps virus was regularly found in the culture medium at levels about 0.9 log higher than the cell-associated virus. When first tested after 30 subcultures, the virus was found to have lost its cytopathogenicity for cells ordinarily susceptible to mumps virus, but was identifiable as mumps virus by neutralization with specific antiserum. Use of fluorescein-labeled antiserum revealed that 80 to 95 per cent of cells in the carrier cultures contained mumps virus antigen. The antigen was concentrated in a few sharply circumscribed, discrete masses in the cell cytoplasm rather than in many granules throughout the cytoplasm as is characteristic of cell infection by cytopathogenic mumps virus. The carrier cultures were resistant to the destructive effect of a cytopathogenic line of mumps virus, but showed little resistance to the cytopathogenic effect of vesicular stomatitis, Sendai, or Newcastle disease viruses.

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