Homologous inhibition with heated and ultraviolet-treated vaccinia virus in cultures of L cells

Abstract

Heated (56°, 45 minutes) vaccinia virus exerts an inhibitory effect upon the growth of homologous infectious virus in L-cell cultures. Cells receiving a multiplicity of about 1000 heated and 10 fresh virus particles exhibit a general toxic response with 5%, or less, of normal virus growth. At lower multiplicities (100 heated plus 10 fresh) viral growth is about 50% of normal, but delay of the fresh virus inoculation results in further reduced growth. At multiplicities of 10 and 3, typical interference develops. In no case was complete interference observed. Minimal virus growth was 5–10% of normal, but its quality (PFU per 1000 particles) was the same as that of fresh inoculum. No incomplete virus production was observed. Inhibitory activity is a property of the virus particles, not of some smaller particulate unit. No interferon has been detected. Heating virus at 60° rapidly destroys inhibitory activity. Virus inactivated with 2537 A ultraviolet rays exhibits inhibitory power only at very high input multiplicities which are toxic to the cells. Evidence is presented which suggests that vaccinia virus preparations may often contain noninfectious particles that exert inhibitory power which modifies the effect of the infectious particles when the particle-cell multiplicity is greater than one.