Role of lymphoid cells in age-related change of susceptibility to Friend leukemia virus-induced leukemia.

Susceptibility for Friend leukemia virus (FLV)-induced leukemogenesis was examined in the C3H/He (C3H)-->C57BL/6 (B6) radiation bone marrow chimeras of various age groups, and the effect of aging of host mice on the susceptibility was determined. The bone marrow chimera system provided the various age of FLV-resistant host mice (B6) possessing the same age of FLV-susceptible target cells from C3H mice. Using this system, we could determine the aging effect on the host resistancy against FLV without an influence of the aging effect on target cells. First, the young C3H-->young B6 chimeras and young C3H-->old B6 chimeras were compared. The young-->old chimeras were more susceptible to FLV-induced acute disease than the young-->young chimeras. The spleen CD4+ as well as CD8+ T cells were reduced in young-->old chimeras compared with young-->young chimeras. Similarly, the old C3H-->old B6 chimeras were more susceptible than old-->young chimeras and revealed the lower CD4+ T cell ratio in the spleen. Discussion was made on the possible implication of these findings on the role of T cells in age-related change of resistance to FLV-induced leukemogenesis.