Response of sublethally irradiated monkeys to a replicating viral antigen

Temporal effects of exposure to sublethal, total-body X radiation (400 R) on responses to vaccination with attenuated Venezuelan equine encephalomyelitis vaccine virus. TC-83, were examined in rhesus monkeys. Viremia, often with delayed onset, was prolonged even when irradiation preceded vaccination by 28 days. Virus titers were increased, articularly in groups irradiated 4 or 7 days before vaccination. Delay in appearance of hemagglutination-inhibition and serum-neutralizing antibody correlated closely with persistence of viremia in irradiated-vaccinated monkeys. The temporal course of antibody response was markedly affected by the intervals between irradiation and injection of this replicating antigen. With longer intervals between irradiation and vaccination, the somewhat depressed antibody responses approached normal or surpassed those of nonirradiated monkeys. Vaccination 14 days after radiation exposure resulted in lethality to 8 of 12 monkeys, apparently as a result of secondary infection. The additional lymphopenic stress due to the effect of TC-83, superimposed on the severly depressed hematopoietic competence at 14 days, undoubtedly contributed to this increased susceptibility to latent infection.