High MOI Research Articles

Regulation of SV40‐induced cell division and tumor antigen by dibutyryl adenosine 3′‐5′‐monophosphate

Simian virus 40 (SV40) induces cell division in microcultures of sparsely plated nongrowing mouse BALB/3T3 cells during acute infection at moderate multiplicities of infection (MOI = 10-100). The infected cells are killed when a MOI of 1,000 is used. SV40 tumor (T) antigen is synthesized in the infected cells, but viral DNA, virion antigen, and progeny virions are not synthesized (abortive infection). The addition of exogenous dibutyryl adenosine 3'-5'-monophosphate (dbcAMP) at the time of infection stimulates the SV40-induced cell division at all MOI and inhibits SV40-induced cell death at high MOI. The percentage of T antigen-positive cells, as monitored by immunofluorescence, is also increased by the addition of dbcAMP at the time of infection. This regulation of SV40-induced cell division and T antigen formation by exogenous dbcAMP occurs within the first 6 hr after infection at 37 degrees C and is dependent upon both the MOI and the concentration of added dbcAMP. The addition of dbcAMP to productively infected TC7 monkey cells has litte effect on the SV40-induced cell death or T antigen formation.

An Unusual Defective Genotype Derived from Herpes Simplex Virus Strain ANG

A defective genotype of herpes simplex virus strain Angelotti (HSV ANG) accumulates in the course of controlled serial high MOI virus passages representing 50-60% of the total number of mature virions in the seventh of these passages. Defective HSV ANG significantly differs from other defective HSV genotypes described so far: the DNA of the defective particles has the same buoyant density as nondefective DNA. In contrast to non-defective HSV ANG DNA, it is not attacked by the restriction endonucleases Eco R I, Hpa I and Hind III. Defective virions strongly suppress the formation of progeny virus. They do not interfere, however, with the synthesis of HSV-specified thymidine (TdR) kinase.

Resistance of hamster cells transformed by herpes simplex virus type 2 to superinfection by herpes simplex viruses.

Cultures of hamster embryo fibroblasts originally trans formed in vitro by herpes simplex virus (HSV) type 2 previously irradiated with ultraviolet light were resistant to superinfection by HSV-1 and HSV-2. The degree of resistance was dependent upon the concentration of the superinfecting virus. At an MOI of 1.0 infectious virus particle per cell, significant virus replication occurred. At an MOI of 0.001 per cell, little or no virus replication was detected. In normal hamster embryo fibroblasts, virus replicated when either high or low MOI were used. Early events in the virus-replicative cycle were found to proceed normally. The results suggest that HSV can initiate and complete the infectious cycle in a limited number of herpes-transformed cells, a finding similar to that observed for Epstein-Barr herpesvirus systems.

Acquisition of sequences homologous to host deoxyribonucleic acid by closed circular simian virus 40 deoxyribonucleic acid.

The synthesis of closed circular simian virus 40 (SV40) deoxyribonucleic acid (DNA) containing sequences homologous to host cell DNA depends upon the conditions under which the cells are infected. When BS-C-1 monkey cells were infected with non-plaque-purified virus at low multiplicity of infection [MOI, 0.032 plaque-forming units (PFU)/cell], little, if any, of the SV40 DNA extracted from the infected cells hybridized to host DNA; but when increasingly higher multiplicities were used (in the range 0.16 to 3,000 PFU/cell), an increasingly greater amount of the extracted SV40 DNA hybridized to host DNA. The same effect was observed when the closed circular SV40 DNA was extracted from purified virions (grown at low and high MOI) rather than from the infected cell complex. When the cells were infected at high MOI with plaque-purified virus (11 viral clones were tested), none of the SV40 DNA extracted from the cells hybridized detectably with host cell DNA. However, plaque-purified virus that was serially passaged, undiluted, induced the synthesis of virus DNA which again showed extensive homology to host DNA. It is suggested that, under certain circumstances, recombination occurs between viral and host DNA during lytic infection which results in the incorporation of host DNA sequences into closed circular SV40 DNA.