Mitigation of Secondary Disease of Allogeneic Mouse Radiation Chimeras by Modification of the Intestinal Microflora

SUMMARY-Conventional CBA mice subjected to lethal whole-body irradiation and allogeneic bone-marrow trans-plantation developed delayed secondary disease, which caused 95 % mortality within 100 days. Symptoms of secondary disease as well as mortality were virtually absent in similarly treated mice kept in the germfree state or given a colonization-resistant (CR) flora. Conventionali-zation of these mice as early as 40 days after transplanta-tion did not induce a significant degree of secondary disease except in 1 group of CR mice derived from con-ventional mice by antibiotic treatment. The acute form of secondary disease occurring after transplantation of allo-geneic spleen cells was much less influenced by the gnoto-biotic conditions, which confirmed the concept that the mortality was caused primarily by severe graft-versus-host