Chronic antigenic stress, immunosenescence and human survivorship over the 3 last centuries: heuristic value of a mathematical model

Peripheral selection rather than thymic involution explains sudden contraction in naive CD4 T-cell diversity with age

A diverse array of T cells is required for defense against pathogens. The naive CD4 T-cell repertoire reaches its peak diversity by early human adulthood and is maintained until older age. Surprisingly, around age 70, this diversity appears to plummet abruptly. A similar qualitative pattern holds for the CD4 T memory-cell population. We used mathematical models to explore different hypotheses for how such a loss of diversity might occur. The prevailing hypotheses suggest that the loss of diversity is due to a decline in emigration of cells from the thymus or a contraction in total number of cells. Our models reject these mechanisms because they yield only a gradual and minimal decline in the repertoire instead of the observed sudden and profound decrease later in life. We propose that an abrupt decline in the repertoire could be caused by the accumulation of mutations (defined here as any cell-intrinsic heritable event) that provide a short-term fitness advantage to a small number of T-cell clones (e.g., by an increased division rate or decreased death rate), with the person as a whole incurring the long-term cost of a decreased ability to fight infections.

Forgive to live: forgiveness, health, and longevity

This study examined multiple types of forgiveness as predictors of mortality and potential psychosocial, spiritual, and health mechanisms of the effects of forgiveness on longevity. Data from a nationally representative sample of United States adults ages 66 and older assessed forgiveness, health, religiousness/spirituality, and socio-demographics (N = 1,232). God's unconditional forgiveness and conditional forgiveness of others initially emerged as statistically significant predictors of mortality risk. However, only conditional forgiveness of others remained a significant predictor of mortality after controlling for religious, socio-demographic, and health behavior variables. Mediators of the association between conditional forgiveness of others and mortality were examined, and a statistically significant indirect effect was identified involving physical health. These findings suggest that conditional forgiveness of others is associated with risk for all-cause mortality, and that the mortality risk of conditional forgiveness may be conferred by its influences on physical health.

PON1 is a longevity gene: results of a meta-analysis

Paraoxonase 1 (PON1) is one of the most studied genes regarding cardiovascular risk, oxidative stress and inflammation. Several lines of evidence suggests that PON1 promotes an atheroprotective effect. Patients carrying PON1 codon 192 QQ genotype display a higher risk of cardiovascular events, the major cause of mortality in the elderly: it can be predicted that gene variants increasing the risk of mortality will be under-represented in long-living individuals. We first reported that PON1 R allele (R+) carriers are significantly more represented in Italian centenarians; subsequently this topic has been addressed by many other groups, and here we report a meta-analysis on 11 studies in different populations selected by a review of the literature available in PubMed and testing the effect of the Q192R polymorphism on human ageing. QUORUM guidelines for meta-analysis have been followed, and a total number of 5962 subjects have been included: 2795 young controls (<65 years of age) and 3167 old subjects (>65 years of age). The Mantel-Haenszel weighting for pooling in presence of a fixed effects model has been applied. The meta-analysis of R carriers showed a significant result with an overall OR of 1.16 (1.04-1.30, 95% CI, p=0.006). The meta-analysis of QR genotype also showed a significant result, with an overall OR of 1.14 (1.02-1.27, 95% CI, p=0.016). The results show that PON1 gene variants at codon 192 impact on the probability of attaining longevity, and that subjects carrying RR and QR genotypes (R+ carriers) are favoured in reaching extreme ages. These results likely represent the counterpart of the effects observed on cardiovascular diseases (CVD), as centenarians and nonagenarians escaped or delayed the onset of the major age-related diseases, including CVD.

Innate immunity and inflammation in ageing: a key for understanding age-related diseases

The process of maintaining life for the individual is a constant struggle to preserve his/her integrity. This can come at a price when immunity is involved, namely systemic inflammation. Inflammation is not per se a negative phenomenon: it is the response of the immune system to the invasion of viruses or bacteria and other pathogens. During evolution the human organism was set to live 40 or 50 years; today, however, the immune system must remain active for much a longer time. This very long activity leads to a chronic inflammation that slowly but inexorably damages one or several organs: this is a typical phenomenon linked to ageing and it is considered the major risk factor for age-related chronic diseases. Alzheimer's disease, atherosclerosis, diabetes and even sarcopenia and cancer, just to mention a few – have an important inflammatory component, though disease progression seems also dependent on the genetic background of individuals. Emerging evidence suggests that pro-inflammatory genotypes are related to unsuccessful ageing, and, reciprocally, controlling inflammatory status may allow a better chance of successful ageing. In other words, age-related diseases are "the price we pay" for a life-long active immune system: this system has also the potential to harm us later, as its fine tuning becomes compromised. Our immune system has evolved to control pathogens, so pro-inflammatory responses are likely to be evolutionarily programmed to resist fatal infections with pathogens aggressively. Thus, inflammatory genotypes are an important and necessary part of the normal host responses to pathogens in early life, but the overproduction of inflammatory molecules might also cause immune-related inflammatory diseases and eventually death later. Therefore, low responder genotypes involved in regulation of innate defence mechanisms, might better control inflammatory responses and age-related disease development, resulting in an increased chance of long life survival in a "permissive" environment with reduced pathogen load, medical care and increased quality of life.

Immunity & Ageing: a new journal looking at ageing from an immunological point of view

In the elderly, many alterations of both innate and clonotypic immunity have been described. Alterations to the immune system in the elderly are generally viewed as a deterioration of immunity, leading to the use of the term immunosenescence. However, although many immunological parameters are often notably reduced in the elderly, retained function of both innate and clonotypic immunity in the elderly is tightly correlated to health status. Recognising the important role of the immune system in ageing, over the last few years, journals oriented towards gerontology and geriatric sciences have increasingly published articles dealing with the immunology of ageing, but a specialised journal in this area does not exist. Immunity & Ageing is a new Open Access, peer reviewed journal that aims to cover all the topics dealing with innate and clonotypic immunity which are relevant to ageing. The journal will provide an opportunity to focus on this topic, which is emerging as one of the critical mechanisms of ageing. Furthermore, as an online, Open Access journal, Immunity & Ageing will promote immediate accessibility to research, which is generally not possible for articles published in printed journals. We hope this forum, concentrating on the themes of ageing and immunology with a strong focus on human studies, will create a new perspective for viewing a world that is inevitably becoming older.

Immunoproteasomes and immunosenescence

Aging is a complex process which is accompanied with the decline and the reshaping of different functions of the body. In particular the immune system is characterized, during ageing (immunosenescence) by a remodeling of innate immunity (well preserved, up-regulated) and clonotypical immunity (severely altered) and by the occurrence of a chronic inflammatory process (inflammaging) which are, at least in part, genetically controlled. In this scenario, it can be anticipated that a crucial role is played by age-related structural and functional alterations and modifications of proteasomes and immunoproteasomes, the last being a key component of antigen processing and MHC class I antigen presentation. A variety of experimental data are available, suggesting that proteasomes are affected by age, and that in centenarians they are relatively preserved. On the contrary, few data are available on immunoproteasomes, likely as a consequence of the poverty of suitable cellular models. Lymphoblastoid cell lines from EBV immortalized B cells from old donors is envisaged as a possible model for the study of immunoproteasomes in humans and their changes with age. Thus, basic questions such as those related to possible consequences, for immune responses in infectious diseases and cancer, of age-related alterations of antigen processing and presenting, change with age of self-antigen repertoire, and the genetic basis of immunoproteasome activity and its change with age, remain largely unanswered.