Accumulation of memory T cells from childhood to old age:: Central and effector memory cells in CD4+ versus effector memory and terminally differentiated memory cells in CD8+ compartment

Memory T cells can be classified as central memory (T-CM, CD45RA(neg)CCR7(+)), effector memory (T-EM, CD45RA(neg)CCR7(neg)), and terminally differentiated cells (T-TD, CD45RA(+)CCR7(neg)) with different homing and effector capacities. In 101 healthy subjects aged from 5 to 96 years, distinct dynamics were evidenced between circulating CD4+ and CD8+ T cell populations. Naive CD4+ and CD8+ T cells decreased linearly with age, CD8+ twice more rapidly. Memory cells outnumbered naive cells on average at 37.4 in the CD4(+) and 29.5 years of age in the CD8+ pool. CD4+ T-CM and T-EM cells were positively correlated and increased linearly at a similar rate with age, while CD4+ TTD remained rare. CD8+ T-EM and TTD accumulated linearly with age, while T-CM increased only slightly, and each memory subset was negatively correlated to the two others. Almost all CD8+ T-TD and some CD8+ T-EM had lost CD28 expression. Despite different dynamics, each individual CD4+ naive and memory subset was correlated to the synonymous CD8+ subset. Half of the subjects aged 65 years or older were characterized by extremely reduced CD8+ naive and increased CD8+ TTD cell counts, which could indicate an acceleration of the decay of the immune system from this age onward. (c) 2005 Elsevier Ireland Ltd. All rights reserved.