Sci. Aging Knowl. Environ., 30 November 2005
Vol. 2005, Issue 48, p. pe37
[DOI: 10.1126/sageke.2005.48.pe37]

PERSPECTIVES

T Cell Immunity and Aging

Sven Dominik Koch, Juergen Kempf, and Graham Pawelec

The authors are at the Center for Medical Research at the University of Tuebingen, D-72072 Tuebingen, Germany. E-mail: sven-dominik.koch{at}student.uni-tuebingen.de (S.D.K.), graham.pawelec{at}uni-tuebingen.de (G.P.)

http://sageke.sciencemag.org/cgi/content/full/2005/48/pe37

Key Words: immunosenescence • heat shock protein • p53 polymorphism • chronic antigenic stimulation • cytomegalovirus • DNA damage and repair

Introduction

The immune system undergoes a variety of changes during aging (see "Immunity Challenge"); T cells, lymphocytes that orchestrate cell-mediated immunity, are particularly vulnerable to the effects of aging. A conference was recently held to provide project participants and invited experts with a scientific update on progress of the European Union's 5th Framework "T Cell Immunity and Ageing" (T-CIA) program (see Koch Perspective) and to review future steps for the next 6 months. Claudio Franceschi (University of Bologna, Italy) and co-workers acted as hosts for this conference on aging, which appropriately took place in Europe�s oldest university in the city of Bologna, 16 to 18 June 2005. Presentations from the meeting are briefly summarized in this Perspective.

Development of an in vitro T Cell Model

One of the core activities of the T-CIA project is to develop an in vitro model of T cell clonal expansion and contraction under conditions of chronic antigenic stress, such as exist in vivo in certain pathological or quasi-pathological states (for example, persistent viral infection, cancer, and possibly autoimmune reactions). To this end, monoclonal T cell populations are generated and aliquots cryopreserved over their entire finite culture life span (ranging up to ~80 population doublings). T cell clones (TCCs) have been derived from centenarians, 85-year-olds, and young donors, and their aging characteristics followed longitudinally in culture. The clones are distributed to project members for concerted investigations of multiple parameters on the same standardized materials. Biomarkers of aging are sought, and interventions to prevent the appearance of these biomarkers are developed. Changes seen in the in vitro clonal models are used as guides to examine alterations ex vivo in T cells from elderly donors.

Heat Shock Proteins

The meeting started with an update and overview on the use of these T cell clones, which are all provided by the Tuebingen Ageing and Tumour Immunology group headed by the T-CIA project coordinator, Graham Pawelec (University of Tuebingen, Germany). Specifically, work from this group has recently focused on the expression and regulation of the heat shock proteins hsp27, hsp72, hsc70 (hsp73), and hsp90{alpha} in TCCs at different in vitro ages and from donors of different ages, as described by Juergen Kempf (University of Tuebingen). No informative alterations in the induction or levels of expression of the constitutively expressed hsc70 or hsp90{alpha} were observed, but preliminary data suggest that the heat stress response as reflected in hsp72 (but not hsp27) expression may distinguish between shorter and longer lived TCCs and that differential regulation of hsp72 may contribute to longevity (see Longo Perspective for further discussion of heat shock proteins and aging).

Genomic and Proteomic Studies

For a broader view of age-associated changes in these TCCs, Dawn Mazzatti (Unilever PLC, Colworth, United Kingdom) presented preliminary genomic and proteomic studies using in-house cDNA arrays for the former and Ciphergen-surface enhanced laser/desorption ionization (SELDI) technology for the latter. Interestingly, gene array data suggested age-associated changes in the expression of genes encoding molecules involved in T cell homing to the endothelium, a process in which T cells are guided through the endothelium by binding to other cells bearing appropriate cell adhesion molecules. This mechanism is very important for certain immunological processes, such as tissue infiltration of immunological cells from the blood to the inflammation site or lymphatic tissue. These molecules include Selectin 1, CD7, CCR7, CXCL10, and other chemokines. Proteomic studies are less well developed, but application of the newest SELDI platform is revealing differences that were less clear in data derived from the old machine. These potential markers are now being analyzed by focused application of mass spectrometry techniques (specifically, matrix-assisted laser desorption/ionization reflectron time-of-flight and Nano-LC-ion trap tandem mass spectrometry).

Attention was drawn to the complexities and potential pitfalls of bioinformatics analysis of gene array data (and these caveats potentially apply to proteomics, too). These were emphasized in the next presentation by Daniel Remondini (University of Bologna), who, together with Gastone Castellani (University of Bologna) is developing innovative "complex network" data analysis methods to handle data from the arrays of 19,000 DNA oligomers employed by D. Mazzatti.

DNA Damage

p53

However, for the foreseeable future, the alternative method of preselecting target gene products of interest based on evidence from other experiments, and examining these products in TCCs and different populations of donors, is still preeminent in efforts to understand and manipulate immune aging. To this end, C. Franceschi presented genetic analyses of p53 and its important polymorphism at codon 72 (resulting in a proline rather than arginine codon at this position), which influences susceptibility to apoptosis and is increased in frequency in centenarians. Thus, codon 72 proline allele carriers (Pro+) have a higher level of expression of the p53-induced p21/WAF1 gene (which mediates cell cycle arrest) in fibroblasts and a lower susceptibility to apoptosis. The functional differences between these two p53 codon 72 alleles may therefore have a broad impact in different aging cells. The p53-mediated response of T cells as well as fibroblasts to DNA damage may well also be influenced by these polymorphisms.

Poly(ADP-ribosyl)ation

DNA damage and repair mechanisms are being investigated in TCCs by Yvonne Barnett (Nottingham Trent University, United Kingdom), who reported a decline in the poly(ADP-ribosyl)ation capacity of TCCs derived from young and middle-aged donors with increasing in vitro culture age. This posttranslational modification is induced by DNA damage and has been linked to DNA repair. In contrast, TCCs derived from very healthy elderly people (selected based on a set of guidelines for very good health, called the SENIEUR protocol) did not show any evidence of such a decline, suggesting that intrinsic differences in the cells from these donors were maintained through extensive rounds of cell division in vitro. Whether these differences are related to polymorphisms in p53 or other genes is not yet known.

Mismatch repair

Associated with genetic damage and chromosomal instability, several dysfunctions in repair mechanisms are conceivable. Simona Neri (University of Bologna) presented data obtained from screening a large number of TCCs from different sources and of different ages for mismatch repair (MMR) capacity and differences in the expression level of the enzymes involved, such as hMutS and hMutL. Malfunctioning MMR leads to microsatellite instability and thus to some age-related diseases. She screened for mutation and methylation in the genes encoding CD4, VWA31, Fes/FPS, Tpox, and p53 (primarily chosen as markers) and found quite remarkable stability in the majority of clones, with the notable exception of those derived from adult CD34+ hematopoietic progenitor cells. The implications of these findings for aging are unclear but may augur ill for stem cell transplantation.

Chronic Antigenic Stimulation

The final session of the meeting focused on the emerging role of chronic antigenic stimulation, especially by cytomegalovirus (CMV), on immunosenescence. CMV is a relatively harmless virus carried by most adults, which may play a role in immune dysfunction in the elderly (see "T Cell Tunnel Vision" and "All Pain, No Gain"). CMV-specific T cells (which carry receptors recognizing CMV peptides) can be identified using tetramer technology. Tetramers are fluorescent staining reagents containing four major histocompatibility (MHC) class I molecules and an antigenic peptide epitope that allow direct staining of antigen-specific T cells. Olga de la Rosa (University of Córdoba, Spain) screened human CMV-specific T cells for surface markers defining naïve T cells (which have never had contact with an antigen) and the various populations of memory cells (which have divided after an initial response to an infection and are ready to respond faster to a second exposure) and effector cells (which carry out immune effector functions, especially cytotoxicity and cytokine production). Using CD45RA, CCR7, and CD27 as markers to distinguish between these subsets, she investigated differential expression of natural killer (NK) cell receptors, such as killer cell immunoglobulin-like receptors and killer cell lectin-like receptors (KLRs), that are also expressed in subpopulations of T cells. The CMV-specific CD8 T cells [that is, cytotoxic T cells that kill only CMV infected cells with foreign CMV peptide on their surface (presented by MHC-class-I molecules)] express high levels of NK cell-associated activating (CD244 and NKG2D) or inhibitory (CD85j) receptors as well as KLRG-1. They also contain large amounts of perforin (a protein that forms tubular transmembrane structures at the sites of cell lysis triggered by NK and cytotoxic T cells). The majority of CMV-specific cells in the elderly are therefore likely to be end-stage effector cells expressing different NK cell receptors with little remaining proliferative capacity.

Following the presentation of these results, Sine Reker (Danish Cancer Society, Copenhagen, Denmark) described the development of the concept of the immune risk phenotype (IRP) in the very elderly, based on longitudinal studies of Swedish octogenarians and nonagenarians (from the work of Anders Wikby, University of Jönköping, Sweden). Using denaturing gradient gel electrophoresis, she found an increased number of CD8 T cell clonal expansions in the nonagenarians as compared with middle-aged people, which were associated with CMV seropositivity. However, in nonagenarian donors with the IRP, there was a significantly lower number of clones compared with non-IRP individuals of the same age, and this characteristic was associated with shorter survival time. This finding may result from clonal expansion eventually resulting in clonal exhaustion, leading to shrinkage of the CD8 repertoire, which is associated with decreased survival. Finally, Milena Ivanova (University of Sofia, Bulgaria) reported on classical immunogenetic studies performed on Bulgarian families with long-lived members, including both human leukocyte antigen typing and evaluation of markers such as CD4, CD8, CD28, CD56, and CD57, as well as sophisticated cytokine polymorphism analyses. These results will be related to CMV viral load. Preliminary analyses, however, do not seem to show a correlation between viral load and the presence of CD8 cells bearing markers of advanced differentiation such as KLRG-1 (Sven Koch, University of Tuebingen).

Concluding Note

At the end of 2005, a final T-CIA conference will take place 13 to 16 December on the edge of the Black Forest in Freudenstadt, Germany. For details, please contact T-CellsInAgeing{at}web.de.


November 30, 2005 Citation: S. D. Koch, J. Kempf, G. Pawelec, T Cell Immunity and Aging. Sci. Aging Knowl. Environ. 2005 (48), pe37 (2005).








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