Unexpected expansions of CD8-bearing cells in old mice.

As mice age, spontaneous changes occur in the receptor repertoire of their T cells. The receptor repertoire of CD4+ T cells does not change with age. By contrast, however, the percentage of alpha beta+, CD8+ T cells bearing particular V elements varies considerably between individual aged mice, although it is remarkably consistent among individual young animals within a given strain. Changes of receptor V element use among CD8+ T cells in individual mice are unpredictable. However, when a large number of mice of the same strain is analyzed, strain-specific trends in V element skewing are found. Old C3H.SW and B10.BR mice have mono- or oligoclonal expansions of CD8+ T cells. These expansions of peripheral CD8+ T cells with age are probably due to deregulation of proliferation of individual CD8+ T cells after recognition of viral or environmental Ag, accompanied, perhaps, by partial transformation of particular T cell clones. Another phenomenon documented herein is the fact that the CD4/CD8 ratio drops steadily as a function of age. Shifts in CD4/CD8 ratio were not due to increased numbers of CD8+ T cells in spleen and lymph nodes, rather the CD4+ T cells disappeared from aging mice faster than CD8+ T cells.