Wen Lin

From the moment of conception, we begin to age. A decay of cellular structures, gene regulation, and DNA sequence ages cells and organisms. DNA methylation patterns change with increasing age and contribute to age related disease. Here we identify 88 sites in or near 80 genes for which the degree of cytosine methylation is significantly correlated with age in saliva of 34 male identical twin pairs between 21 and 55 years of age. Furthermore, we validated sites in the promoters of three genes and replicated our results in a general population sample of 31 males and 29 females between 18 and 70 years of age. The methylation of three sites--in the promoters of the EDARADD, TOM1L1, and NPTX2 genes--is linear with age over a range of five decades. Using just two cytosines from these loci, we built a regression model that explained 73% of the variance in age, and is able to predict the age of an individual with an average accuracy of 5.2 years. In forensic science, such a model could estimate the age of a person, based on a biological sample alone. Furthermore, a measurement of relevant sites in the genome could be a tool in routine medical screening to predict the risk of age-related diseases and to tailor interventions based on the epigenetic bio-age instead of the chronological age.

The population dynamics that enable a small number of regulatory T (T(R)) cells to control the immune responses to foreign Ags by the much larger conventional T cell subset were investigated. During the primary immune response, the expansion and contraction of conventional and T(R) cells occurred in synchrony. Importantly, the relative accumulation of T(R) cells at peak response significantly exceeded that of conventional T cells, reflecting extensive cell division within the T(R) cell pool. Transfer of a polyclonal T(R) cell population before immunization antagonized both polyclonal and TCR transgenic responses, whereas blocking T(R) cell function enhanced those responses. These results define an inverse quantitative relationship between T(R) and conventional T cells that controls the magnitude of the primary immune response. The high frequency of dividing T(R) cells suggests degenerate TCR specificity enabling activation by a broad spectrum of Ags.

In addition to thymus-derived or natural T regulatory (nT(reg)) cells, a second subset of induced T regulatory (iT(reg)) cells arises de novo from conventional CD4(+) T cells in the periphery. The function of iT(reg) cells in tolerance was examined in a CD45RB(high)CD4(+) T cell transfer model of colitis. In situ-generated iT(reg) cells were similar to nT(reg) cells in their capacity to suppress T cell proliferation in vitro and their absence in vivo accelerated bowel disease. Treatment with nT(reg) cells resolved the colitis, but only when iT(reg) cells were also present. Although iT(reg) cells required Foxp3 for suppressive activity and phenotypic stability, their gene expression profile was distinct from the established nT(reg) "genetic signature," indicative of developmental and possibly mechanistic differences. These results identified a functional role for iT(reg) cells in vivo and demonstrated that both iT(reg) and nT(reg) cells can act in concert to maintain tolerance.