Studies on the restriction of herpes simplex virus type 1 multiplication in neuroblastoma cells

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Multiplication of herpes simplex virus type 1 (HSV-1) was restricted in neuroblastoma cell line IMR-32 pretreated with cyclic AMP (cAMP) at 37 C for 6 days and cultured in the presence of cAMP. Maximum effect was obtained at a concentration of 0.5 to 1.0 mM. The effect was specific to cAMP and neuroblastoma cell-type. The inhibitory effect of cAMP was reduced, if MOI was raised over 0.01 or if the concentration of fetal bovine serum in medium was increased above 1%. Serum lots used for cultivation influenced the inhibitory effect of cAMP. The finding indicated that serum contains factor(s) antagonizing the inhibitory effect of cAMP. In this study the selected lots of serum were employed to reduce a fluctuation of cAMP-induced restriction of HSV-1 multiplication.Removal of cAMP from infected cell cultures caused the initiation of viral multiplication, indicating that the inhibitory effect of cAMP was reversible. When the incubation temperature was lowered to 34.5 C, the viral multiplication occurred even in the presence of cAMP. A shift-up of incubation temperature from 34.5 to 38.5 C strongly inhibited the viral multiplication. The infectivity of free virus decreased irrespective of the presence or absence of cAMP, if the suspension was incubated at 38.5 C. On the other hand, the viral growth was observed even at 38.5 C, when cAMP was removed from the culture medium. Therefore, cAMP-induced restriction of viral multiplication was not due to inactivation of mature virus yielded from infected cells but due to inhibition of viral growth in neuroblastoma cells.Viral multiplication remained to be restricted, when verapamil, <Ca^(2+)> antagonist, was added to the infected culture at the time cAMP was removed. Phorbol ester did not induce viral multiplication, if the drug was added to cAMP-treated cell cultures. The mechanism of restriction of HSV-1 multiplication in cAMP-treated neuroblastoma cells remains to be clearified.