Age-related changes of T cell subsets in intestinal intraepithelial lymphocytes of mice.

Age-related changes in T cell subsets were examined in intestinal intraepithelial lymphocytes (i-IEL), which contain unique T cells differentiating extrathymically. In 2-month-old mice bred under conventional condition, i-IEL consisted of a large number of CD4-CD8 alpha/alpha+ cells bearing either T cell receptor (TcR)alpha/beta or TcR gamma/delta and only a few CD4+CD8 alpha- cells. In aged mice (6 months old and 24 months old), unique CD4+CD8 alpha/alpha+ i-IEL bearing TcR alpha/beta increased in number and conversely the proportion of TcR gamma/delta+ i-IEL was decreased. Such an increase in number of CD4+CD8 alpha/alpha+ cells was detected in i-IEL from aged (14-months old) nude mice, but not in aged (14 months old) germ-free mice, suggesting that a significant fraction of TcR alpha/beta T cells such as CD4+CD8 alpha+ i-IEL can develop along an extrathymic pathway under the influence of intestinal microflora with age.