Printed in Great Britain The Effect of 5-Bromodeoxyuridine on Interferon Production in Human Cells

5-Bromodeoxyuridine (BrdUrd) increased interferon production by the Namalwa line of human lymphoblastoid cells treated with Sendai virus, but inhibited their growth. Thymidine, which also inhibited cell growth had no effect on interferon production, so that growth inhibition per se was not the cause of the stimulation. BrdUrd was incorporated into cellular DNA; 5-chlorodeoxyuridine and 5-iodo-deoxyuridine (which are also incorporated) increased the interferon yield, but 5-fluorodeoxyuridine (which is not incorporated) did not. Thymidine reduced both the incorporation of BrdUrd and its stimulatory effect on interferon pro-duction. Deoxycytidine (which prevents the cytotoxic effects of BrdUrd) had no effect on the stimulation. BrdUrd also stimulated interferon production in response to poly(rI).poly(rC) in growing human diploid fibroblasts but not in SV4o virus-transformed human cells. Since BrdUrd was incorporated into the DNA of all these cells, we concluded that incorporation is necessary, but not sufficient for the stimulation of interferon formation