Stimulating Interaction between Viruses (stimulons) by Charles Chany and Carlos Brailovsky

During previous investigations on the viral autoinhibition phenomenon' it was observed that interferon was detected in the culture medium of viral-infected cells but not in extracts of these cells. It was suggested that viral-infected cells may contain a substance antagonistic to interferon, a substance which, unlike interferon, diffuses poorly into the surrounding culture medium. Further studies to explore this hypothesis were complicated because of the considerable quantities of interferon produced in most of the cell-virus systems described. The recent observation in our laboratory of a "stimulating effect" on one virus by another virus permitted further investigation of this phenomenons 3 A stimulating interaction between viruses can be defined in the following manner: when two or more antigenically related or unrelated viruses infect the same cell in a certain chronological order, the inducing agent stimulates the multiplication of the challenge virus. Stimulating interaction consequently represents a reverse phenomenon of the interference phenomenon as usually understood by virologists. Several hostvirus relationships of this kind have been observed and reported in the literature.20-22, 24, 29 In this report only the "stimulating interaction" between adenovirus 12 and Kilham's rat virus will be presented in detail. It was postulated that this system might prove useful in the study of the hypothetical factor antagonistic to interferon, since neither adenovirus 12 nor K rat virus produce significant amounts of interferon in rat cells.3 Thus the "antagonistic factor" would not be masked by the presence of interferon. In rat cells adenovirus 12 does not induce the production of virions or even structural antigens in detectable quantities, although T antigens are formed and can be detected in the cell by the use of fluorescent antibody techniques.4' Furthermore, some of the cells in these infected cultures undergo malignant transformation in vitro."5 6 The Kilham rat virus induces a lytic cycle in rat embryonic cells with the production of fully infectious particles and hemagglutinin.7 Both adenovirus and rat virus are DNA viruses and both multiply within the cell nucleus. Material and Methods.-Cell culture system: Rat embryonic fibroblasts (REF): Ten-day-old pregnant Wistar rats were obtained from the breeding colony of the Cancer Institute, Villejuif, France. In some instances rats raised in germ-free conditions were obtained through the courtesy of Dr. Saquet from the laboratory of germ-free animals of the CNRS, Gif sur Yvette, France. In order to avoid external contamination, the gravid uterus was placed in a solution containing Formalin, 30%c; Germibac, 250 ml; water, q.s.p., 51. The embryos obtained after incision of the uterus were then trypsinized and the cells cultured in a slightly modified Eagle's medium plus 10% calf serum in 1-liter Roux bottles. The first subculture was employed for all tests. Human embryonic kidney cells (HEK): Human embryonic kidney cells were trypsinized and ('ltivated in 1-liter Roux bottles with 10% calf serum and Eagle's medium. For cell maintenance the concentration of the serum was reduced to 5%.