INTERFERENCE INDUCED AGAINST VACCINIA IN AN ADENOVIRUS-RHF-1 SYSTEM

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Abstract
It was observed that a continuous line of rabbit heart cell culture (strain RHF-1), when overlaid with growth medium after infection of cultures with adenovirus types 2, 3, 4, and 7, would develop resistance to vaccinia plaque formation. Data are presented to provide some information on the nature of such resistance observed specifically in an adenovirus 2-RHF-1 system. An analysis of this phenomenon indicated the following. (i) At least 6 hr were required before the start of vaccinia inhibition, and 15 to 18 hr were necessary for the maximal occurrence of inhibition; the degree of interference established varied with the concentration of adenovirus. (ii) The site of interference action was inside rather than outside the cells, since hardly any difference could be shown in the rate of vaccinia adsorption on resistant and susceptible cells. (iii) The interaction of adenovirus with RHF-1 cells not only would inhibit cell infection with vaccinia but would also suppress the 24- to 48-hr yield of virus. (iv) When RHF-1 cells were overlaid with maintenance medium after their infection with a low multiplicity of RHF-1 passaged adenovirus 2 (to establish sublethal infection), an inhibitory substance of varied activity could be detected daily over a period of at least 10 days which, when transferred to normal RNF-1 cultures, would render them resistant to vaccinia infection. (v) Although limited growth of virus appeared to be responsible for the production of the inhibitor, increase in inhibitory activity did not seem to coincide with increase in virus titer. (vi) The inhibitor seemed to resemble interferons in inhibiting virus plaque production, but its exact identity and the mode of action remain to be determined.