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Incidence of delayed mortality (secondary disease) in allogeneic radiation chimeras receiving bone marrow from aged mice.


 The effect of donor age on the reactivity of bone marrow from a long-lived hybrid mouse in the pathogenesis of secondary disease in young, lethally irradiated, allogeneic recipient mice was studied. The influence of the thymus on potential effector cells in the bone marrow was also examined in marrow donors and in allogeneic recipients. In contrast to the marked reduction in the humoral immune response with senescence in this hybrid, the ability of bone marrow from old donors to precipitate secondary disease was more than equivalent to that of the corresponding tissue from young donors in both tempo and severity of reaction. Thymectomy of the donors at 2 months of age or a combination of adult thymectomy and sublethal irradiation did not diminish the severity of the disease; host thymectomy only temporarily retarded the course of the reaction but not the final cumulative mortality. The results are compatible with the existence of a large, long-lived, stable population of cells, reactive in initiating delayed mortality, which does not diminish appreciably with senescence.