Stimulation of hemolysin plaque-forming cells by idoxuridine

5-Iodo-2'-deoxyuridine markedly stimulates the production of hemolysin plaque-forming cells (HPFC) to sheep red blood cells in C3HeB/FeJ and A/J male and female mice. The degree of stimulation is dose dependent over a range of 50 to 200 mg/kg. Stimulation is observed when drug is given on the day of antigen administration, or up to 3 days thereafter, but not when given before antigen administration or 4 days thereafter. The stimulatory effect of IUdR given on day 2 after antigen is still noted on Day 15, but the time of HPFC production is not prolonged beyond that in controls. Both 19S and 7S HPFC are increased, although the effect on the latter is less pronounced. In addition to stimulating production of HPFC in immunized animals, 5-iodo-2'-deoxyuridine increases background HPFC production in nonimmunized mice by 250% when assayed on the day after treatment.