The initial age-associated decline in early T-cell progenitors reflects fewer pre-thymic progenitors and altered signals in the bone marrow and thymus microenvironments.

Age-related thymus involution results in decreased T-cell production, contributing to increased susceptibility to pathogens and reduced vaccine responsiveness. Elucidating mechanisms underlying thymus involution will inform strategies to restore thymopoiesis with age. The thymus is colonized by circulating bone marrow (BM)-derived thymus seeding progenitors (TSPs) that differentiate into early T-cell progenitors (ETPs). We find that ETP cellularity declines as early as 3 months (3MO) of age in mice. This initial ETP reduction could reflect changes in thymic stromal niches and/or pre-thymic progenitors. Using a multicongenic progenitor transfer approach, we demonstrate that the number of functional TSP/ETP niches does not diminish with age. Instead, the number of pre-thymic lymphoid progenitors in the BM and blood is substantially reduced by 3MO, although their intrinsic ability to seed and differentiate in the thymus is maintained. Additionally, Notch signaling in BM lymphoid progenitors and in ETPs diminishes by 3MO, suggesting reduced niche quality in the BM and thymus contribute to the early decline in ETPs. Together, these findings indicate that diminished BM lymphopoiesis and thymic stromal support contribute to an initial reduction in ETPs in young adulthood, setting the stage for progressive age-associated thymus involution.

Integrative transcriptome and chromatin landscape analysis reveals distinct epigenetic regulations in human memory B cells.

Memory B cells (MBCs) are long-lived and produce high-affinity, generally, class-switched antibodies. Here, we use a multiparameter approach involving CD27 to segregate naïve B cells (NBC), IgD+ unswitched (unsw)MBCs and IgG+ or IgA+ class-switched (sw)MBCs from humans of different age, sex and race. Conserved antibody variable gene expression indicates that MBCs emerge through unbiased selection from NBCs. Integrative analyses of mRNAs, miRNAs, lncRNAs, chromatin accessibility and cis-regulatory elements uncover a core mRNA-ncRNA transcriptional signature shared by IgG+ and IgA+ swMBCs and distinct from NBCs, while unswMBCs display a transitional transcriptome. Some swMBC transcriptional signature loci are accessible but not expressed in NBCs. Profiling miRNAs reveals downregulated MIR181, and concomitantly upregulated MIR181 target genes such as RASSF6, TOX, TRERF1, TRPV3 and RORα, in swMBCs. Finally, lncRNAs differentially expressed in swMBCs cluster proximal to the IgH chain locus on chromosome 14. Our findings thus provide new insights into MBC transcriptional programs and epigenetic regulation, opening new investigative avenues on these critical cell elements in human health and disease.

CMV induces expansion of highly polyfunctional CD4+ T cell subset coexpressing CD57 and CD154.

CD4+ T cells are essential for human CMV infection control. CMV-specific CD4+ T cells possess antiviral functions and participate in anti-CMV humoral/cellular responses. In the elderly, CMV infection impairs immunity to other viruses and has been traditionally associated with T cell senescence; however, recent results suggest that, in younger people, CMV confers immune protection against other pathogens (heterologous immunity). To shed light on this controversy, we analyzed latent CMV infection effects on the quality of young individuals' immune response, specifically, the presence of polyfunctional T cells through an extensive phenotypic and functional characterization of the CD4+ T cell subset. CD154 expression, degranulation (CD107a), and cytokine production (IFN-γ, TNF-α, and IL-2) as well as T cell phenotype markers (CD57, CD28, and CD27) were analyzed. We demonstrate that CD4+ T cells that coexpress CD57 and CD154, which are exclusively present in CMV-positive individuals, are the most polyfunctional CD4+ subset, whereas CD4+CD27+CD28- T cells associate with lower polyfunctionality. Conversely, the frequency of CD4+CD28+ T cells correlates with higher polyfunctionality of CD4+CD57- T cells from CMV-seronegative individuals and CD4+CD57+CD154+ T cells from CMV-seropositive individuals. Thus, polyfunctionality is a property of central memory CD4+ T cells in CMV-seronegative individuals, whereas after CMV infection, polyfunctional T cells become highly differentiated, which allows efficient eradication of infections. We extend previous observations of the impact of CMV on CD8+ T cell functionality to the CD4+ T cell compartment, revealing CD57 as a polyfunctionality marker of T cells which expands after CMV infection. CD57+ T cells have been associated with inflammatory conditions, but their potential role in the response against infectious disease and vaccination should now be investigated.

Vδ2+ and α/ß T cells show divergent trajectories during human aging.

Chronological aging and a variety of stressors are driving forces towards immunosenescence. While much attention was paid to the main T cell component, α/ß T cells, few studies concentrate on the impact of age on γ/δ T cells' characteristics. The latter are important players of adaptive immunity but also have features associated with innate immunity. Vδ2+ are the main component of γ/δ while Vδ1+ T cells expand upon Cytomegalovirus (CMV) infection and with age. The Vδ2+ T cells are not influenced by persistent infections but do contribute to immunosurveillance against bacterial pathogens. Here, we focus on Vδ2+ T cells and report that their composition and functionality is not altered in older adults. We have performed a side-by-side comparison of α/ß and Vδ2 cells by using two robust markers of T cell replicative history and cell differentiation (CD28 and CD27), and cytokine secretion (IFN-γ and TNF-α). Significant differences in Vδ2 versus α/ß homeostasis, as well as phenotypic and functional changes emerged. However, the data strongly suggest a sustained functionality of the Vδ2 population with age, independently of the challenge. This suggests differential trajectories towards immunosenescence in α/ß and Vδ2+ T cells, most likely explained by their intrinsic functions.

Markers of T-cell senescence and physical frailty: insights from Singapore Longitudinal Ageing Studies.

BACKGROUND: Elderly individuals have an eroded immune system but whether immune senescence is implicated with the development of frailty is unknown. The underlying immune mechanisms and the link between markers of senescence and physical frailty is not well established. METHODS: We explored the association of specific T-cell subset markers of immune differentiation and senescence on CD4+ and CD8+ cells (CD28-, CD27- and CD57+) and the immune risk profile (inverted CD4/CD8 ratio <1) with physical frailty among 421 participants who were frail (N=32), prefrail (N=187) and robust (N=202) in the Singapore Longitudinal Ageing Study cohort. RESULTS: In ordinal logistic regression models relating tertile category rank scores of immune biomarker with frailty status (robust, prefrail and frail), CD8+CD28-CD27+ (odds ratio (OR)=1.35, P=0.013), CD4+CD28-CD27+ (OR=1.29, P=0.025), CD8+CD28- (OR=1.31, P=0.022), and CD4/CD8 ratio (OR=1.27, P=0.026) were positively associated with frailty, controlling for age, sex and multimorbidity. CD4/CD8 ratio less than one was not associated with frailty (OR=0.84, P=0.64). In stepwise multinomial logistic regression controlling for age, sex and comorbidity, only CD8+CD28-CD27+ was the independent predictor of prefrailty: highest tertile of the immune marker significantly predicted prefrailty (versus low tertile, OR=1.72, P=0.037) and frailty (OR=2.56, P=0.06). CONCLUSION: The study supports the hypothetical role of immune senescence in physical frailty, particularly in regard to the observed loss of CD28 expression from both CD8+ cells and CD4+ cells, but not for CD27 or CD4/CD8 ratio as a marker of senescence. The potential of CD8+CD28-CD27+ as a biological marker of frailty should be further investigated in prospective studies.

Genome-wide analysis of the genetic regulation of gene expression in human neutrophils.

Neutrophils are an abundant immune cell type involved in both antimicrobial defence and autoimmunity. The regulation of their gene expression, however, is still largely unknown. Here we report an eQTL study on isolated neutrophils from 114 healthy individuals of Chinese ethnicity, identifying 21,210 eQTLs on 832 unique genes. Unsupervised clustering analysis of these eQTLs confirms their role in inflammatory responses and immunological diseases but also indicates strong involvement in dermatological pathologies. One of the strongest eQTL identified (rs2058660) is also the tagSNP of a linkage block reported to affect leprosy and Crohn's disease in opposite directions. In a functional study, we can link the C allele with low expression of the ß-chain of IL18-receptor (IL18RAP). In neutrophils, this results in a reduced responsiveness to IL-18, detected both on the RNA and protein level. Thus, the polymorphic regulation of human neutrophils can impact beneficial as well as pathological inflammatory responses.

γ/δ T cell subsets in human aging using the classical α/ß T cell model.

Aging is associated with an increased susceptibility to infections and diseases. It has also been associated with reduced functionality and altered distribution of immune cells, especially T cells. Whereas classical α/ß T cells, especially CD8(+) T cells, were shown to be highly susceptible to aging, the effects of viral persistent stimulations on the fate of γ/δ T cells are much less documented. Healthy, elderly individuals of Chinese ethnical background were recruited under the aegis of SLAS-II. In this observational study, γ/δ T cell populations were characterized by flow cytometry and compared with the α/ß CD4(+) and CD8(+) T cells in elderly and young controls. In our study, we identified a reduced frequency of γ/δ T cells but not α/ß T cells with aging. The classical markers of α/ß T cell aging, including CD28, CD27, and CD57, did not prove significant for γ/δ T cells. The extreme range of expression of these markers in γ/δ T cells was responsible for the lack of relationship between γ/δ T cell subsets, CD4/CD8 ratio, and anti-CMV titers that was significant for α/ß T cells and, especially, CD8(+) T cells. Although markers of aging for γ/δ T cells are not clearly identified, our data collectively suggest that the presence of CD27 γ/δ T cells is associated with markers of α/ß T cell aging.

The immune system in the aging human.

With the improvement of medical care and hygienic conditions, there has been a tremendous increment in human lifespan. However, many of the elderly (>65 years) display chronic illnesses, and a majority requires frequent and longer hospitalization. The robustness of the immune system to eliminate or control infections is often eroded with advancing age. Nevertheless, some elderly individuals do cope better than others. The origin of these inter-individual differences may come from genetic, lifestyle conditions (nutrition, socio-economic parameters), as well as the type, number and recurrence of pathogens encountered during life. The theory we are supporting is that chronic infections, through life, will induce profound changes in the immune system probably due to unbalanced inflammatory profiles. Persistent viruses such a cytomegalovirus are not eliminated and are a driven force to immune exhaustion. Because of their age, elderly individuals may have seen more of these chronic stimulators and have experienced more reactivation episodes ultimately leading to shrinkage of their repertoire and overall immune robustness. This review integrates updates on immunity with advancing age and its impact on associated clinical conditions.