Journal
CLINICAL IMMUNOLOGY
Volume 94, Issue 3, Pages 160-172Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1006/clim.1999.4832
Keywords
T lymphocytes; memory cells; CD8(+) T lymphocytes; CD28 expression; T cell clonal expansions
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With advancing age, healthy humans frequently demonstrate large clonal expansions of CD8(+) T cells in the peripheral blood, which persist for long periods of time and appear to be maintained as a population of memory cells. We studied nine large T cell clones in five elderly individuals. We noted that in most cases the expanded clones were dominated by cells that did not express CD28, a pivotal molecule in T cell activation, and these clones proliferated poorly in culture. However, nearly all of the clonal expansions had CD28(+) fractions and some of these cells appeared to lose CD28 gene expression with stimulation in culture. CD28(+) cells demonstrated greater proliferation in both bulk and limiting dilution cultures compared to CD28(-) cells bearing the same TCR, whereas CD28(-) cells showed increased perforin expression. Together, these data suggest that loss of CD28 expression maths functional differentiation to cytotoxic memory cells within these clonal expansions and likely within CD8(+) memory populations in general. (C) 2000 Academic Press.
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