Null cell senescence and its potential significance to the immunobiology of aging.

The null cell compartments of human bone marrow and mouse spleen were arbitrarily divided into three subpopulations based upon the ability of cells to acquire T or B cell membrane markers when incubated with poly A:U or ubiquitin. There was an accumulation of T cell precursors with congenital absence of the thymus. In contrast, T cell precursors were reduced and there was an accumulation of uninduced null cells with old age. These observations suggest that there is an intrinsic defect of null cell differentiation with a drift towards more differentiated precursors in T cell differentiation with aging. This could result in a diminution in the range of responses by their progeny, mature T lymphocytes.