Researchers discuss the failing, age-damaged immune system: "At present, individuals can live up to 80-120 years, a time much longer than that of our ancestors, as a consequence of the improvements in life conditions and medical care. Thus, the human immune system has to cope with a lifelong and evolutionarily unpredicted exposure to a variety of antigens, which are at the basis of profound age-related changes globally indicated as immunosenescence, a multifaceted phenomenon that increases morbidity and mortality due to infections and age-related pathologies. The major changes occurring during immunosenescence are the result of the accumulation of cellular, molecular defects and involutive phenomena (such as thymic involution) occurring concomitantly to a hyperstimulation of both innate and adaptive immunity (accumulation of expanded clones of memory and effector T cells, shrinkage of the T cell receptor repertoire, progressive activation of macrophages), and resulting in a low-grade, chronic state of inflammation defined as inflammaging. It is unknown whether inflammaging, which represents a risk factor for most age-related pathologies, is a cause or rather an effect of the aging process. ... centenarians seem to be equipped with gene variants that allow them to optimize the balance between pro- and anti-inflammatory molecules, and thus to minimize the effects of the lifelong exposure to environmental insults and stressors."

Link: http://www.ncbi.nlm.nih.gov/pubmed/19047800