A reduced peripheral blood CD4(+) lymphocyte proportion is a consistent ageing phenotype

Peripheral blood leukocyte composition was measured in young, middle-aged and old C57BL/6J (B6) and BALB/cByJ (BALB) mice by flow cytometry to test the hypothesis that ageing is associated with declines in the proportions of peripheral blood T lymphocytes. In both B6 and BALB mice, increasing age is associated with a significant and continuous decline in the proportions of CD4(+) lymphocytes, a moderate decline in the proportion of CD8(+) lymphocytes, a significant increase in the proportion of Gr1(+) granulocytes and an almost unchanged proportion of B lymphocytes. As expected, the proportion of CD44(low) naive T lymphocytes decreased with age. Expression of Fas (CD95(+)) on CD4(+) and CD8(+) lymphocytes showed no consistent change with age. We also measured peripheral blood CD4(+) and CD8(+) lymphocyte proportions in young and old A/J, CBA/CaJ, DBA/2J, DW/J and (DWxC3H) F1 mice. The CD4(+) lymphocyte proportion decreased from young to old age in these strains by 56,65,72,78 and 68%, respectively. The CD8(+) lymphocyte proportion decreased moderately with age in all the inbred strains tested but not in the (DWxC3H) F1 hybrid. Thus, a reduced proportion of peripheral blood CD4(+) lymphocytes is a consistent ageing phenotype in a wide range of Mus musculus strains.