Establishment and characterization of a persistent infection of MDBK cells with herpes simplex virus.

A persistent, dynamic-state infection of a variant of herpes simplex virus type 1 strain MP [HSV-1 (MP)] in MDBK cells was established without supportive measures and maintained for over three years by routine passaging of the cells at 7-9 day intervals. The infection was characterized by a cyclic pattern of monolayer damage and reconstitution, correlated with virus production, which was most evident when the interval between subcultures was intentionally prolonged and the cells were left undisturbed. Occasional periods of cell crisis, with increased virus replication and extensive cytopathology, occurred. Passaging of the cells at higher density avoided eventual loss of the culture during the most severe crises. Presence of specific antibodies did not alter the course of infection. Interferon was constantly found during periods of cell crisis; it appeared on the second day after subculture, reached a maximum in correspondance of the first peak of cytopathology, and disappeared well before the onset of the second wave of cytopathology. Addition of exogenous interferon cured the cells of infection. Defective interfering particles could not be found. Virus isolated during persistence differed from parental virus regarding plaque morphology, temperature sensitivity of growth, and electrophoretic pattern of infected cells glycoproteins. A discussion on the possible mechanisms of persistence is provided.