Age-sensitive T cell phenotypes covary in genetically heterogeneous mice and predict early death from lymphoma

A novel role for CD4+ T cells in the control of cachexia

Cachexia is the dramatic weight loss and muscle atrophy seen in chronic disease states, including autoimmunity, cancer, and infection, and is often associated with lymphopenia. We have previously shown that CD4(+) T cells that express the lowest density of CD44 (CD4(+)CD44(v.low)) are significantly reduced in diabetic NOD mice that are cachexic compared with diabetic mice that are not cachexic. Using this model, and a model of cancer cachexia, we test the hypothesis that CD4(+)CD44(v.low) cells play an active role in protecting the host from cachexia. CD4(+)CD44(v.low) cells, but not CD4(+) cells depleted of CD44(v.low) cells, delay the onset of wasting when infused into either diabetic or prediabetic NOD recipients. However, no significant effect on the severity of diabetes was detected. In a model of cancer cachexia, they significantly reduce muscle atrophy, and inhibit muscle protein loss and DNA loss, even when given after the onset of cachexia. Protection from wasting and muscle atrophy by CD4(+)CD44(v.low) cells is associated with protection from lymphopenia. These data suggest, for the first time, a role for an immune cell subset in protection from cachexia, and further suggest that the mechanism of protection is independent of protection from autoimmunity.

Cachexia in the non-obese diabetic mouse is associated with CD4+ T-cell lymphopenia

One of the long-term consequences of Type I diabetes is weight loss with muscle atrophy, the hallmark phenotype of cachexia. A number of disorders that result in cachexia are associated with immune deficiency. However, whether immune deficiency is a cause or an effect of cachexia is not known. This study examines the non-obese diabetic mouse, the mouse model for spontaneous Type I diabetes, as a potential model to study lymphopenia in cachexia, and to determine whether lymphopenia plays a role in the development of cachexia. The muscle atrophy seen in patients with Type I diabetes involves active protein degradation by activation of the ubiquitin-proteasome pathway, indicating cachexia. Evidence of cachexia in the non-obese diabetic mouse was determined by measuring skeletal muscle atrophy, activation of the ubiquitin-proteasome pathway, and apoptosis, a state also described in some models of cachexia. CD4+ T-cell subset lymphopenia was measured in wasting and non-wasting diabetic mice. Our data show that the mechanism of wasting in diabetic mice involves muscle atrophy, a significant increase in ubiquitin conjugation, and upregulation of the ubiquitin ligases, muscle RING finger 1 (MuRF1) and muscle atrophy F box/atrogin-1 (MAFbx), indicating cachexia. Moreover, fragmentation of DNA isolated from atrophied muscle tissue indicates apoptosis. While CD4+ T-cell lymphopenia is evident in all diabetic mice, CD4+ T cells that express a very low density of CD44 were significantly lost in wasting, but not non-wasting, diabetic mice. These data suggest that CD4+ T-cell subsets are not equally susceptible to cachexia-associated lymphopenia in diabetic mice.

Alteration of intestinal intraepithelial lymphocytes after massive small bowel resection

BACKGROUND

Intraepithelial lymphocytes (IEL) comprise the inner most layer of the gut immune system, and play a critical role in protecting the host from enteric organisms. Massive small bowel resection (MSBR) is one such clinical condition where patients are at particularly high risk for the development of such enteric infectious complications. Because of this, we hypothesized that the IEL may change significantly after the formation of a MSBR. To address this, a mouse model of MSBR was created and the acute phenotypic and functional characteristics of the IEL were studied.

MATERIALS AND METHODS

Mice underwent a 70% mid-small bowel resection. After 7 days, IEL were isolated and analyzed for phenotypic changes by flow cytometry. IEL cytokine expression was performed with semiquantitative polymerase chain reaction techniques. To assess the functional significance of these changes, IEL proliferative response was assessed in vitro.Results. MSBR led to significant decreases in specific IEL subpopulations: CD 44+ (used as a marker of cell maturity); CD 8alphabeta+ (marker of thymic derivation), and CD 69+ (marker of T cell activation). Compared with controls, IEL TNF-alpha mRNA expression increased 84%, while IL-2 and IL-10 mRNA expression decreased by 69 and 72%, respectively. Spontaneous proliferation of IEL in the MSBR group was significantly higher than controls, however, proliferation failed to increase with T cell stimulation.Conclusion. These changes suggest a shift to a more immature and possibly less activated cell population. It is possible that such alterations may play an important role in the increase in enterically derived infections in patients with MSBR.

Value of immunological markers in predicting responsiveness to influenza vaccination in elderly individuals

Elderly individuals are at high risk for morbidity and mortality when infected with influenza virus. Vaccinations with inactivated virus are less effective in the elderly due to the declining competency of the aging immune system. We have explored whether immunological parameters predict poor anti-influenza virus vaccine responses and can be used as biological markers of immunosenescence. One hundred fifty-three residents of community-based retirement facilities aged 65 to 98 years received a trivalent influenza vaccine. Vaccine-induced antibody responses were determined by comparing hemagglutination inhibition titers before and 28 days after immunization. The composition of the T-cell compartment was analyzed by flow cytometry and the sizes of three T-cell subsets, CD4(+) CD45RO(+) cells, CD4(+) CD28(null) cells, and CD8(+) CD28(null) cells, were determined. Only 17% of the vaccine recipients were able to generate an increase in titers of antibody to all three vaccine components, and 46% of the immunized individuals failed to respond to any of the three hemagglutinins. The likelihood of successful vaccination declined with age and was independently correlated with the expansion of a particular T-cell subset, CD8(+) CD28(null) T cells. The sizes of the CD4(+) CD45RO(+) memory T-cell and CD4(+) CD28(null) T-cell subsets had no effect on the ability to mount anti-influenza virus antibody responses. Frequencies of CD8(+) CD28(null) T cells are useful biological markers of compromised immunocompetence, identifying individuals at risk for insufficient antibody responses.

Activated CD8(+) T cells from aged mice exhibit decreased activation-induced cell death

To uncouple the defects of activation and apoptosis of T cells from aged mice, we used anti-CD3 plus IL-2 stimulation to induce an activation response and analyzed the subsequent activation-induced cell death (AICD) response of T cells from 16-month-old mice. The results herein demonstrate that T cells from 16-month-old mice could be activated by anti-CD3-induced activation signals but exhibited distinct phenotypic and functional features compared to young (2-month-old) mice. These include a decrease in AICD, a delayed entry into the cell cycle, and a decreased telomerase activity. The decreased AICD of T cells from 16-month-old mice is associated with a decreased expression of Fas and Fas ligand (FasL), decreased susceptibility to anti-Fas-induced apoptosis, and an increased expansion of a CD8(+) T-cell population. Prior to activation, these T cells exhibit a phenotype that is CD44(hi)CD62L(hi). After stimulation, these T cells produced high levels of the pro-inflammatory cytokine, IFN-gamma, and developed an increased population of IFN-gamma(+)IFN-gamma R(-) T cells. Our results suggest that there is a dysregulation in T-cell homeostasis in aged mice associated with a decrease in AICD of CD8(+) T cells.

Intrinsic and environmental influences on immune senescence in the aged monkey

Several factors associated with the age-related decline in immunity were examined in three studies on aged rhesus monkeys. Natural killer (NK) cell activity was found to be low in many monkeys after 20 years of age, but exceptionally long-lived animals, older than 25 years, often had vigorous cytolytic responses. When NK activity was decreased in an aged monkey, it was predictive of fewer years of survival and a younger age at death. This prediction of mortality was associated with one nonimmune biomarker of aging in the monkey: nail growth rate. Monkeys with very slow nail growth and low NK activity were likely to die sooner. Although these findings might suggest an immutable course for the aging process, the housing conditions of old monkeys also had a pronounced effect on their NK activity. The highest NK responses were found in old monkeys housed with just one other old animal when compared to living alone or with just a young, juvenile monkey. It remains to be determined whether this type of psychosocial influence could have a sustained effect on immunity and ultimately change the pace of aging and time to mortality.

Immunogenetics of longevity. Is major histocompatibility complex polymorphism relevant to the control of human longevity? A review of literature data

Literature data suggest that human longevity may be directly correlated with optimal functioning of the immune system. Therefore, it is likely that one of the genetic determinants of longevity resides in those polymorphisms for the immune system genes that regulate immune responses. Accordingly, studies performed on mice have suggested that the Major Histocompatibility Complex (MHC), known to control a variety of immune functions, is associated with the life span of the strains. In the last 25 years, a fair number of cross-sectional studies that searched for the role of HLA (the human MHC) genes on human longevity by comparing HLA antigen frequencies between groups of young and elderly persons have been published, but conflicting findings have been obtained. In fact, the same HLA antigens are increased in some studies, decreased in others and unchanged in others. On the whole, that could lead us to hypothesize that the observed age-related differences in the frequency of HLA antigens are due to bias. In our opinion, this hypothesis is real for most studies owing to major methodological problems. However, some studies that do not meet these biases have shown an association between longevity and some HLA-DR alleles or HLA-B8,DR3 haplotype, known to be involved in the antigen non-specific control of immune response. Thus, HLA studies in man may be interpreted to support suggestions derived from the studies on congenic mice on MHC effects on longevity. However, in mice the association may be by way of susceptibility to lymphomas whereas, in human beings, the effect on longevity is likely, via infectious disease susceptibility. Longevity is associated with positive or negative selection of alleles (or haplotypes) that respectively confer resistance or susceptibility to disease(s), via peptide presentation or via antigen non-specific control of the immune response.

Biomarkers of aging: prediction of longevity by using age-sensitive T-cell subset determinations in a middle-aged, genetically heterogeneous mouse population

Seven T-cell subset values were measured in each of 559 mice at 8 months of age, and then again in the 494 animals that reached 18 months of age. The group included virgin males, virgin females, and mated females, and it was produced by using a four-way cross-breeding system that generates genetic heterogeneity equivalent to a very large sibship. An analysis of covariance showed that four T-cell subsets-CD4, CD4 memory, CD4 naïve, and CD4 cells expressing P:-glycoprotein-were significant predictors (p <.003) of longevity when measured at 18 months of age after adjustment for the possible effects of gender and mating. The subset marked by CD4 and P:-glycoprotein expression showed a significant interaction effect: this subset predicted longevity only in males. Among subsets measured when the mice were 8 months of age, only the levels of CD8 memory cells predicted longevity (p =.016); the prognostic value of this subset was largely limited to mated females. A cluster analysis that separated mice into two groups based upon similarity of T-cell subset patterns measured at 18 months showed that these two groups differed in life expectancy. Specifically, mice characterized by relatively low levels of CD4 and CD8 memory cells, high levels of CD4 naïve cells, and low levels of CD4 cells with P:-glycoprotein (64% of the total) lived significantly longer (50 days = 6%; p <.0007) than mice in the other cluster. The results are consistent with the hypothesis that patterns of T-cell subsets vary among mice in a manner than can predict longevity in middle age, and they suggest that these subsets may prove to be useful for further studies of the genetics of aging and age-sensitive traits.

Age-dependent alterations in the assembly of signal transduction complexes at the site of T cell/APC interaction

TCR interaction with peptide-MHC complexes triggers migration of protein kinases, actin-binding proteins, and other accessory molecules to the T cell/APC synapse. We used confocal immunofluorescence methods to show that the adapter protein LAT (linker for activation of T cells) and the guanine nucleotide exchange factor Vav also move to the APC interface in mouse CD4 T cells conjugated to anti-CD3 hybridoma cells, and in TCR-transgenic CD4 cells conjugated to APC bearing agonist (but not closely related nonagonist) peptides. The proportion of CD4+ T cells able to relocalize LAT or Vav, or to relocate cytoplasmic NT-AT (NF-ATc) from cytoplasm to nucleus, declines about 2-fold in aged mice. The decline in LAT relocalization is accompanied by a similar decline in tyrosine phosphorylation of LAT in CD4 cells stimulated by CD3/CD4 cross-linking. Two-color experiments show that LAT redistribution is strongly associated with relocalization of both NF-ATc and protein kinase C-theta among individual cells. LAT migration to the immunological synapse depends on actin polymerization as well as on activity of Src family kinases, but aging leads to only a small change in the percentage of CD4 cells that redistribute F-actin to the site of APC contact. These results suggest that defects in the ability of T cells from aged donors to move kinase substrates and coupling factors, including LAT and Vav, into the T cell/APC contact region may contribute to the decline with age in NF-ATc-dependent gene expression, and thus to defects in T cell clonal expansion.

Regulation of extrathymic T cell development and turnover by oncostatin M

Chronic exposure to oncostatin M (OM) has been shown to stimulate extrathymic T cell development. The present work shows that in OM transgenic mice, 1) massive extrathymic T cell development takes place exclusively the lymph nodes (LNs) and not in the bone marrow, liver, intestines, or spleen; and 2) LNs are the sole site where the size of the mature CD4+ and CD8+ T cell pool is increased (6- to 7-fold). Moreover, when injected into OM transgenic mice, both transgenic and nontransgenic CD4+ and CD8+ T cells preferentially migrated to the LNs rather than the spleen. Studies of athymic recipients of fetal liver grafts showed that lymphopoietic pathway modulated by OM was truly thymus independent, and that nontransgenic progenitors could generate extrathymic CD4+CD8+ cells as well as mature T cells under the paracrine influence of OM. The progeny of the thymic-independent differentiation pathway regulated by OM was polyclonal in terms of Vbeta usage, exhibited a phenotype associated with previous TCR ligation, and displayed a rapid turnover rate (5-bromo-2'-deoxyuridine pulse-chase assays). This work suggests that chronic exposure to OM 1) discloses a unique ability of LNs to sustain extrathymic T cell development, and 2) increases the number and/or function of LN niches able to support seeding of recirculating mature T cells. Regulation of the lymphopoietic pathway discovered in OM transgenic mice could be of therapeutic interest for individuals with thymic hypoplasia or deficient peripheral T cell niches.

Lifelong treatment with oral DHEA sulfate does not preserve immune function, prevent disease, or improve survival in genetically heterogeneous mice

OBJECTIVES

To determine whether lifelong exposure to dehydroepiandrosterone sulfate extends the lifespan or retards immune senescence in mice.

DESIGN

Double-blind, placebo-controlled intervention trial.

SETTING

A specific pathogen-free rodent vivarium.

PARTICIPANTS

120 mice bred as a cross between CB6F1 females and C3D2F1 males.

INTERVENTION

DHEAS at 100 microg/mL in drinking water from weaning until death.

MEASUREMENT

Age at death, cause of death, antibody production after erythrocyte immunization, and T cell subset profiles in peripheral blood at ages 8 and 18 months.

RESULTS

DHEAS ingestion did not lead to a significant increase in mean or maximal longevity: the 95% confidence interval for DHEAS effect on mean lifespan ranged from +35 days to -80 days. There were no significant effects of DHEAS on incidence of lethal illnesses, except for a trend toward higher levels of mammary adenocarcinoma in DHEAS-treated females and mouse urinary syndrome in DHEAS-treated males. DHEAS treatment did not improve the ability of middle-aged mice to produce antibody to a foreign particulate antigen, and it did not alter the proportions of age-sensitive T cell subsets in middle-aged animals.

CONCLUSION

Although differences among species in pharmacokinetics complicate interpretation of studies in which DHEA or DHEAS is administered to rodents, our data provide no support for the idea that chronic exposure to this steroid retards immune senescence or prevents late life illness.

Genes as gerontological variables: genetically heterogeneous stocks and complex systems

In gerontological research utilizing animal models, a major general strategy has been the use of uniform genotypes of inbred strains or their F1 hybrids. These animal models provide standard reference groups that are of major importance in establishing a reliable data base on aging phenomena. There are limitations to their usage, however, particularly in respect to descriptions or evaluations of variances or of covariance relationships. For these purposes, genetically heterogeneous stocks have the advantage that phenotypic variance (and covariance) has a genetic as well as an environmental component. The advantages of genetic heterogeneity are best realized when the stock has been systematically derived (usually by intercrossing of inbred strains) and maintained by a mating scheme of sufficient size to minimize inbreeding. Genetically heterogeneous stocks are of particularly high potential value in the study of complex systems. Some examples of their use in a gerontological context are provided.

Multiple-trait quantitative trait loci analysis using a large mouse sibship

Quantitative trait loci influencing several phenotypes were assessed using a genetically heterogeneous mouse population. The 145 individuals were produced by a cross between (BALB/cJ x C57BL/6J)F1 females and (C3H/HeJ x DBA/2J)F1 males. The population is genetically equivalent to full siblings derived from heterozygous parents, with known linkage phase. Each individual in the population represents a unique combination of alleles from the inbred grandparents. Quantitative phenotypes for eight T cell measures were obtained at 8 and 18 mo of age. Single-marker locus, repeated measures analysis of variance identified nine marker-phenotype associations with an experimentwise significance level of P < 0.05. Six of the eight quantitative phenotypes could be associated with at least one locus having experiment-wide significance. Composite interval, repeated measures analysis of variance identified 13 chromosomal regions with comparisonwise (nominal) significance associations of P < 0.001. The heterozygous-parent cross provides a reproducible, general method for identification of loci associated with quantitative trait phenotypes or repeated phenotypic measures.

Age-related changes in T cell surface markers: a longitudinal analysis in genetically heterogeneous mice

In a longitudinal design in which each animal was examined repeatedly throughout its life, we used flow cytometry to determine the numbers or proportions of a variety of T lymphocyte subsets in the peripheral blood of mice aged 8-20 months. Half of the 128 mice were given a low calorie diet which is known to extend lifespan and to reduce the rate of age-associated change in T cell immune function. In these genetically heterogeneous mice, bred as the progeny of CB6F1 females and C3D2F1 males, aging led to statistically significant increases in the number of CD3 cells and the proportions of CD4 memory and CD8 memory cells, and declines in the proportions of CD4 cells and CD4 virgin cells. Older mice also had increased proportions of CD4 and CD8 cells that were able to extrude the fluorochrome R123 through the action of P-glycoprotein. Caloric restriction delayed or prevented most of these age-dependent changes, but had little effect on expression of P-glycoprotein. Correlation analysis showed that those individual mice with high levels of CD4 memory or CD8 memory T cells tended also to have relatively low levels of CD4 virgin cells and low proportions of CD4 T cells, particularly at older ages. In addition, those mice which had the greatest rate of increase in CD4 memory and CD8 memory T cells also tended to show the greatest decline in CD4 virgin and in the proportion of CD4 cells. High numbers of CD4R (and high rates of change in the CD4R subset) were associated with high numbers (and change scores) for the CD8R subset, but there were no strong correlations between the R123-extruding subsets and other age-sensitive markers. Thus some, but not all, age-sensitive T cell subsets show correlated levels and correlated rates of change throughout the middle of the lifespan.

Increased apoptosis of CD45RO- T cells with aging

Increasing susceptibility to infectious and autoimmune phenomena have long been recognized to accompany advancing age in otherwise healthy individuals. Recently animal models of aging have suggested that age-associated immune dysfunction may correlate with defects in T cell apoptosis. We have examined activation-induced apoptosis defects in human peripheral T cells from young individuals (mean age = 31 +/- 3 years old) compared to aged individuals (mean age = 67 +/- 8 years old). Following in vitro activation of T cells with PHA and IL-2, apoptosis was measured in T cell subsets using 7-amino actinomycin D (7-AAD) staining and analysis via three colour flow cytometry. There was no significant difference in apoptosis of the total CD3+ T cell population at early and late time points. Interestingly, increased apoptosis in the CD3+ CD45RO- T cell population of older adults was observed by culture day 6. While the total number of CD3+ CD45RO- cells was not different between young (< 33 years) and old (> 65 years) individuals, 32% of these cells did not undergo apoptosis in younger individuals while only 10% of these cells avoided this fate in older individuals. These results suggest that accumulation of CD45RO+ T cells may occur in aged subjects due in part to preferential elimination of CD45RO- cells with activation. Furthermore, as new or continued immune response requires differentiation of CD45RO+ T cells to CD45RO+ T cells after activation, increased apoptosis instead of survival in aged individuals could lead to observed T cell immune deficiency.

The T cell in the ageing individual

Aged persons frequently manifest declining parameters of those immune functions which protect the young against disease. Longitudinal studies are beginning to show that number, type and function of T cells may be associated with longevity, morbidity and mortality in free-living elderly humans. Multi-faceted alterations in the ability of T cells from old donors to respond to stimulation are being dissected, and pathways which are compromized in the elderly compared to the young are being defined. Successful immune responses depend upon waves of rapid and extensive clonal expansion to combat primary infection, followed by death of most T cells, survival of memory cells and their later reactivation and further expansion. This implies that the finite replicative potential of T cells might impose a critical limiting factor on the maintenance of immune responses in the face of thymic involution and drastically reduced capacity to generate new naive T cells. This type of 'clonal exhaustion' can readily be studied in vitro using human T cell clones and the findings can be applied to the in vivo situation. Understanding the processes of replicative senescence in such in vitro models may shed light not only on some of the underlying mechanisms of immunosenescence but also in situations of chronic antigenic stimulation in vivo. Moreover, it might begin to indicate how the system could be manipulated on the one hand to prevent or reverse T cell senescence without nullifying the control mechanisms of tumor suppression, and on the other hand, to reconstitute possibly faulty suppression, for example in autoimmune disease.

Lifespan and lesions in genetically heterogeneous (four-way cross) mice: a new model for aging research

Genetically heterogeneous animal models provide many advantages for research on aging but have been used infrequently. We present here lifespan and lesion data from a study of mice bred as a cross between (AKR/J x DBA/2J)F1 females and (C57BL/6J x SJL/J)F1 males. In such a four-way cross population, each mouse is genetically unique, but replicate populations of essentially similar genetic structure can be generated quickly, at low cost, and of arbitrary size from commercially available, genetically stable hybrid parents. We employed a protocol in which mice judged to be severely ill were euthanatized to obtain tissue in optimal condition for necropsy, and we were able to infer a likely cause of illness in 42 of 44 animals. Malignant lymphoma, including at least four histopathologically distinct subtypes, was the most common cause and was also a frequent incidental finding in mice dying of other causes. Neoplastic disease, benign or malignant, was the sole or a contributing cause of illness in 90% of the mice for which a cause could plausibly be assigned. A wide range of lethal and nonlethal degenerative lesions was also noted. The coefficient of variation for lifespan in these genetically heterogeneous mice was 26%, similar to that seen in analyses of recombinant inbred mouse lines. Baseline lifespan and pathology data on four-way cross mice is a useful prelude to the exploitation of this rodent model in tests of genetic and mechanistic hypotheses about aging.

The aging immune system: primer and prospectus

Changes in T lymphocyte populations underlie much of the age-related decline in the protective immune response. Aging leads to the replacement of virgin T cells by memory T cells and to the accumulation of cells with signal transduction defects. Studies of antibody gene assembly, accessory cell function, post-thymic T cell development, skewed selection of T cell receptor repertoire, and the clinical concomitants of immune senescence will shed new light on the causes and consequences of age-dependent immune failure.