Raquel Tarazona

Innate immunosenescence: effect of aging on cells and receptors of the innate immune system in humans.

Components of the innate immune response, including neutrophils and macrophages, are the first line of defense against infections. Their role is to initiate an inflammatory response, phagocyte and kill pathogens, recruit natural killer cells (NK), and facilitate the maturation and migration of dendritic cells that will initiate the adaptive immune response. Extraordinary advances have been made in the last decade on the knowledge of the receptors and mechanisms used by cells of the innate immunity not only to sense and eliminate the pathogen but also to communicate each other and collaborate with cells of adaptive immunity to mount an effective immune response. The analysis of innate immunity in elderly humans has evidenced that aging has a profound impact on the phenotype and functions of these cells. Thus altered expression and/or function of innate immunity receptors and signal transduction leading to defective activation and decreased chemotaxis, phagocytosis and intracellular killing of pathogens have been described. The phenotype and function of NK cells from elderly individuals show significant changes that are compatible with remodeling of the different NK subsets, with a decrease in the CD56bright subpopulation and accumulation of the CD56dim cells, in particular those differentiated NK cells that co-express CD57, as well as a decreased expression of activating natural cytotoxicity receptors. These alterations can be responsible of the decreased production of cytokines and the lower per-cell cytotoxicity observed in the elderly. Considering the relevance of these cells in the initiation of the immune response, the possibility to reactivate the function of innate immune cells should be considered in order to improve the response to pathogens and to vaccination in the elderly.

Immunological biomarkers of ageing in man: changes in both innate and adaptive immunity are associated with health and longevity.

Scientific and clinical advances in the last century have led to increased numbers of individuals living to older ages. Thus a major concern is how to live these years with a high quality of life. The ageing immune system is less well able to cope with infectious diseases than the youthful immune system probably as a consequence of altered immune response to pathogens. Thus, both innate and adaptive immune responses show age-related changes that could be decisive for healthy ageing and survival. Longitudinal studies in healthy elderly have allowed the definition of the ″immune risk phenotype” (IRP) a predictor of mortality in elderly individuals that is based on several parameters of the adaptive immune response. Here, we hypothesize that failures in innate immunity observed in frail elderly are related to those alterations described in adaptive immunity defined as the IRP. It will be important to include assays of NK cell markers and functions in future longitudinal studies in order to investigate this point in detail as well as to consider the trace element zinc as an essential co-factor for optimal NK cell activity.

Selective depletion of CD56dim NK cell subsets and maintenance of CD56bright NK cells in treatment-naive HIV-1-seropositive individuals

Human immunodeficiency virus-1 (HIV-1) infected patients show a gradual loss of natural killer (NK) cells that correlates with disease progression. However, the effect of HIV-1 infection on different NK cell subsets has not been fully characterized. In healthy individuals most NK cells are CD3−CD56+ and two different subpopulations, CD56dim and CD56bright, can be distinguished by the mean fluorescence intensity. Although it was originally suggested that CD56bright NK cells represent the precursors of the CD56dim subpopulation, recent cumulative data indicate that CD56bright and CD56dim NK cells are phenotypically, functionally, and developmentally different NK cell subsets. In this study, the analysis of CD56bright and CD56dim NK subsets showed that neither the number nor the phenotype of CD56bright NK cells were significantly altered in treatment-naive HIV-1-infected individuals, whereas the number of CD56dim NK cells was decreased. We also have studied NK cell subsets defined by the expression of CD56 in combination with CD16, CD161, or CD94 molecules. Our results demonstrated a preferential decrease of CD3−CD56+ NK cells coexpressing CD16 and CD161 but lacking CD94 molecules. On the contrary an increased percentage of NK cells that do not express CD56 molecules but express CD16, CD161, or CD94 was also found in HIV-1-infected individuals. As it has been proposed that these CD56-negative NK cells expressing other NK cell receptors represent immature NK cells with low cytolytic capacity, our results support that a defective differentiation from immature CD56 negative NK cells to mature CD56dim NK cells occurs in HIV-1 infection.

Immunosenescence of human natural killer cells.

Natural killer (NK) cells are a key component of innate immunity involved not only in the elimination of virus-infected or tumor cells but also in the regulation of the immune response by producing cytokines and chemokines that can activate other cellular components of innate and adaptive immunity. NK cell subsets are differentially affected by aging. Whereas CD56bright cells are decreased in healthy elderly individuals, the CD56dim subset is expanded. The expression of CD57, a marker of highly differentiated NK cells, is increased in the elderly; this supports the notion that a remodeling process of NK cell subsets occurs in aging with a gradual decrease in more immature CD56bright NK cells and an increase in highly differentiated CD56dim CD57+ NK cells. This NK cell redistribution can explain many of the phenotypic and functional changes in NK cells associated with healthy aging such as decreased proliferation and the maintenance of CD16-dependent cytotoxicity.

CMV and Immunosenescence: from basics to clinics

Alone among herpesviruses, persistent Cytomegalovirus (CMV) markedly alters the numbers and proportions of peripheral immune cells in infected-vs-uninfected people. Because the rate of CMV infection increases with age in most countries, it has been suggested that it drives or at least exacerbates “immunosenescence”. This contention remains controversial and was the primary subject of the Third International Workshop on CMV & Immunosenescence which was held in Cordoba, Spain, 15-16th March, 2012. Discussions focused on several main themes including the effects of CMV on adaptive immunity and immunosenescence, characterization of CMV-specific T cells, impact of CMV infection and ageing on innate immunity, and finally, most important, the clinical implications of immunosenescence and CMV infection. Here we summarize the major findings of this workshop.

Immunosenescence: Implications for response to infection and vaccination in older people

People aged 60 and older represent over 11% of the world population and it is expected to rise 22% by 2050. Population aging is associated to an increased frequency of age-related diseases including higher susceptibility to infections, cancer, cardiovascular and neurodegenerative diseases. Immunosenescence refers to the decline of the immune system associated to aging. It affects both, innate and adaptive immunity limiting the response to pathogens and to vaccines. The analyses of the immune system in elderly individuals determined several immune signatures constituting an immune risk phenotype that predicts mortality. An inverse CD4/CD8 ratio, loss of naïve T cells, increased numbers of terminally-differentiated T cells and oligoclonal expansions of virus-specific T cells constitute hallmarks of immunosenescence. Natural killer (NK) cells are also found severely altered in the elderly. The contribution of latent cytomegalovirus infection to immunosenescence of T and NK cells has been shown. Considering the worldwide ageing of the population in the next decades, the impact of infections will be a real health problem for older individuals requiring preventive strategies. Thus, further studies are required to analyse the bases of immunosenescence and to establish protocols to overcome the age-associated alterations of the immune response in order to define effective vaccines against those pathogens, such as influenza, contributing to increased morbidity and mortality in the elderly.

Immunomodulatory potential of human adipose mesenchymal stem cells derived exosomes on in vitro stimulated T cells

In the recent years, it has been demonstrated that the biological activity of mesenchymal stem cells (MSCs) is mediated through the release of paracrine factors. Many of these factors are released into exosomes, which are small membranous vesicles that participate in cell–cell communication. Exosomes from MSCs are thought to have similar functions to MSCs such as repairing and regeneration of damaged tissue, but little is known about the immunomodulatory effect of these vesicles. Based on an extensive bibliography where the immunomodulatory capacity of MSCs has been demonstrated, here we hypothesized that released exosomes from MSCs may have an immunomodulatory role on the differentiation, activation and function of different lymphocyte subsets. According to this hypothesis, in vitro experiments were performed to characterize the immunomodulatory effect of human adipose MSCs derived exosomes (exo-hASCs) on in vitro stimulated T cells. The phenotypic characterization of cytotoxic and helper T cells (activation and differentiation markers) together with functional assays (proliferation and IFN-γ production) demonstrated that exo-hASCs exerted an inhibitory effect in the differentiation and activation of T cells as well as a reduced T cell proliferation and IFN-γ release on in vitro stimulated cells. In summary, here we demonstrate that MSCs-derived exosomes are a cell-derived product that could be considered as a therapeutic agent for the treatment of inflammation-related diseases.

Decreased expression of DNAM-1 on NK cells from acute myeloid leukemia patients.

This study tested the hypothesis that the expression of CD112 and CD155 (DNAM‐1 ligands) on leukemic blasts induces a decreased expression of the activating receptor DNAM‐1 on natural killer (NK) cells from acute myeloid leukemia (AML) patients. DNAM‐1 is a co‐receptor involved in the activation of NK cell cytotoxicity after its interaction with its ligands CD112 and CD155 on target cells. Here we study the expression of DNAM‐1 on NK cells and DNAM‐1 ligands on blasts from AML patients stratified by age. The results demonstrate that NK cells from AML patients younger than 65 years have a reduced expression of DNAM‐1 compared with age‐matched controls. The analysis of DNAM‐1 ligands showed a high expression of CD112 and CD155 on leukemic blasts. An inverse correlation between CD112 expression on leukemic blasts and DNAM‐1 expression on NK cells was found. Furthermore, downregulation of DNAM‐1 was induced on healthy donors’ NK cells after in vitro culture with leukemic blasts expressing DNAM‐1 ligands. In conclusion, these results support the hypothesis that receptor–ligand crosslinking downregulates DNAM‐1 expression on NK cells from patients <65 years of age. Considering the relevance of DNAM‐1 in NK recognition and killing of leukemic cells, the reduced expression of this receptor on NK cells from AML patients can represent an additional mechanism of tumor escape.

Vα24+ NKT cells are decreased in elderly humans

Natural killer T (NKT) cells represent a novel cell lineage characterized by the restricted expression of an invariant TCRα chain encoded by Vα24/JαQ gene segments in humans and Vα14/Jα281+ in mice. Different aspects of the immune response are severely affected by age. Thus, we have studied the effect of aging on NKT cells from healthy elderly individuals. Our results demonstrated a decreased percentage of CD3+Vα24+ cells in peripheral blood from elderly donors, whereas mainstream T lymphocytes showed an age-associated decrease in the expression of CD28, the vast majority of CD3+Vα24+ cells from old individuals were CD28+. A significant increase in the percentage of Vα24+ cells with the CD4−CD8+ phenotype was also found in the elderly, indicating a redistribution of Vα24+ subsets according to the CD4/CD8 phenotype. Given the important immunoregulatory role of these cells, the decrease of NKT cells will contribute to the deleterious immune response in the elderly.

Expression of killer inhibitory receptors on cytotoxic cells from HIV-1-infected individuals.

Dysfunction of cytotoxic activity of T and natural killer (NK) lymphocytes is a main immunological feature in patients with AIDS, but its basis are not well understood. It has been recently described that T and NK cell‐mediated cytotoxicity can be regulated by HLA killer inhibitory receptors (KIR). In this work, we have determined on cytotoxic T cells and NK cells from HIV‐1‐infected individuals the expression of the following KIR molecules: p58, p70, and ILT2 (immunoglobulin‐like family KIR) as well as CD94 and NKG2A (C‐lectin‐type family KIR). With some exceptions, no significant changes were found on the expression of immunoglobulin‐like KIR in either CD8+ or CD56+ cells. Interestingly, the percentages of CD8+ and CD56+ cells expressing CD94 were significantly increased in these individuals. We also show that, in vitro, IL‐10 up‐regulates CD94 expression on CD8+ and CD56+ cells obtained from normal individuals, suggesting that the augmented expression observed in HIV‐infected individuals could be related to the high levels of IL‐10 previously described in HIV‐1‐infected individuals.