Accelerated Replicative Senescence of the Peripheral Immune System Induced by HIV Infection

Objectives: HIV induces rapid turnover of T lymphocytes but whether this leads to replicative senescence of CD4+ and CD8+ cells and contributes to AIDS symptoms is unclear. The aim of this study was to address this question by analyzing telomere length in blood cell populations as a measure of replicative history in a significant number of patients infected with HIV.

Design: Total peripheral blood mononuclear cells (PBMCs), CD4+ or CD8+ cells were isolated from blood collected from a total of 73 HIV patients and 27 controls. Samples were isolated to measure telomere length, telomerase activity and proliferative ability, and analyses were carried out in a blind experimental protocol.

Methods: PBMCs isolated on Ficoll-Hypaque gradients were washed and prepared for additional fractionation into CD4+ and CD8+ cells using antibody-bound magnetic beads. Total PBMCs, CD4+ and CD8+ cells were used for cell cycle analysis, for telomerase activity assays and were measured for telomere length using the terminal restriction fragment assay.

Results: Telomere analyses in this study show a clear (P < 0.0001) inverse relationship between telomere length and progression of immunosuppression, with HIV infection resulting in a five-fold or greater acceleration of aging of the circulating PBMC component of the immune system. Patients who are 37 years old showed telomere lengths similar to uninfected 75-year-olds. Telomere loss correlated well with progression of AIDS and with reduced proliferative ability of patient PBMCs but was unrelated to telomerase activity. Mean telomere length was shorter in both CD4+ and CD8+ cells, with three-fold higher rates of telomere loss for CD8+ lymphocytes.

Conclusions: These data provide strong support for the occurrence of accelerated replicative aging of the peripheral immune system, possibly resulting in a loss of T cells leading to AIDS symptoms.