This data suggests that monocytes adhering to vascular endothelium and entering the vessel wall in type diabetes are from a population with shorter telomeres and at increased risk of replicative senescence within vascular plaque.T elomeres are tandem repeats of the DNA sequence TTAGGG extending over kb at the end of eukaryotic chromosomes and are necessary for bo th success fulDNA replication and chromosomal integrity. The costs of publication of this article were defrayed in part by the payment of page charges.This article must therefore be hereby marked advertisement in accordance with U.Many of the dysfunctionsdescribedinv ascul arendothelial cells in type diabetes, as well as in ageing and atherosclerosis, are similar to the phenotype of in vitro senescent vascular endothelial cells. Telomere attrition has attracted attention as a possible associate of cardiovascular disease, vascular senescence, and vascular ageing. It has also been suggested that in utero programming of telomere length contributes to later risk of cardiovascular disease and type diabetes. There are no adequate data on telomere length and DNA damage in human type diabetes, and we hypothesized that type diabetic patients would demonstrate shorter telomeres in peripheral monocytes and lymphocyte subsets compared with control subjects and that this would be directly related to markers of oxidative DNA damage.Subjects with type diabetes were recruited if they had never received gliclazide, antihypertensives, or ACE inhibitors, which have antioxidant or antiinammatory properties. The type diabetic patients were treated with diet alone, metformin and sulfonylureas in combination. Control subjectswithoutdiabetes were recru ited from the general population and met the same inclusion criteria, and none were taking any medication.PBMC were washed once, cryopreserved in liquid nitrogen, and stored until analysis.The cells were washed in PBS and ant ibod ies crosslinked to the cell surface by the addition of mmoll bis and incubated for min at C.In brief, the surfacestained cells were centrifuged and resuspended in either hybridization buffer as negative control cells.The cells were heated at C for min in a water bath, followed by hybridization at room temperature overnight in the dark.Cells were then incubated twice for min at C with wash buffer.Cells were centrifuged and resuspended in ul PBS azide.The cells stained with antiCDAF were then incubated with anti CDRAPE for min at C, washed once, and resuspended in ul of PBS azide.A subsaturating amount of aminoactinomycin was added to all cells, to identify and remove aggregates from subsequent analysis, and incubated for at least min before acquisition of at least, events. Monocytes were identied as C D, na ve T cellsasC D CD RA, andmemoryT cellsasCDCDRA.The mean telomere uorescence was calculated as the difference between the mean uorescence of cells hybridized in the presence of the FITCPNA probe and the background control cells.The assay is an in vitro uorescent proteinbinding method used to detect oxidative DNA in xed permeabilized cells.The probe is specic for oxoguanine, whichisformed during free radical damage to DNA and is a sensitive and specic indicator of oxidative DNA damage with paraformaldeyde for min on ice, washed once with PBS, and resuspended in ethanol and kept at C until staining.