Mouse liver contains both IL-2R beta(-)(or low positive) high T-cell r
eceptor (TCRhi) cells and IL-2R beta(+) intermediate TCR (TCRint) cell
s, TCRint cells consist of natural killer 1.1 (NK1)(+) and NK1(-) subs
ets. NK1(-)TCR(int) cells increase constantly with age whereas TCRhi c
ells decrease, NK1(+) TCRint cell proportions in the liver increase un
til middle age and decrease thereafter. Although NK1(+) TCRint cells i
n other organs are few regardless of age, NK1(-) TCRint cells graduall
y appear in other lymphoid organs with aging. Skewed usage of V beta 7
and V beta 8 TCR was observed in NK1(+) TCRint cells in the liver but
the predominance was less obvious in NK1(-) TCRint and TCRhi cells in
the liver and other organs. TCR V alpha 14 messenger RNA (mRNA) was d
etected in NK1(+) TCRint cells but not in the other two populations, I
n contrast, although NK1(+) TCRint cells contain virtually no V alpha
11(+) T cells, NK1(-) TCRint cells contain a much higher proportion (a
pproximately 12%) of V alpha 11(+) T cells, whereas approximately 4% o
f TCR cells are V alpha 11(+). NK activities of liver mononuclear cell
s (MNC) and splenocytes decrease with aging, although the former is al
ways greater than the latter. NK activity of liver MNC is a function o
f NK cells, partly NK1(+) TCRint cells but not NK1(-) TCRint cells or
TCRhi cells. These results suggest that lymphocytes of liver and other
organs at old age are no longer occupied solely by conventional thymu
s-derived T cells, and the increase of extrathymic IL-2R beta(+) NK1(-
) TCRint cells in liver and periphery could be closely related to immu
nological changes with aging.