Increased expression of major histocompatibility complex antigens on lymphocytes from aged mice

Seasonal and geographic variation in packed cell volume and selected serum chemistry of platypuses

Platypuses (Ornithorhynchus anatinus) inhabit the permanent rivers and creeks of eastern Australia, from north Queensland to Tasmania, but are experiencing multiple and synergistic anthropogenic threats. Baseline information of health is vital for effective monitoring of populations but is currently sparse for mainland platypuses. Focusing on seven hematology and serum chemistry metrics as indicators of health and nutrition (packed cell volume (PCV), total protein (TP), albumin, globulin, urea, creatinine, and triglycerides), we investigated their variation across the species' range and across seasons. We analyzed 249 unique samples collected from platypuses in three river catchments in New South Wales and Victoria. Health metrics significantly varied across the populations' range, with platypuses from the most northerly catchment, having lower PCV, and concentrations of albumin and triglycerides and higher levels of globulin, potentially reflecting geographic variation or thermal stress. The Snowy River showed significant seasonal patterns which varied between the sexes and coincided with differential reproductive stressors. Male creatinine and triglyceride levels were significantly lower than females, suggesting that reproduction is energetically more taxing on males. Age specific differences were also found, with juvenile PCV and TP levels significantly lower than adults. Additionally, the commonly used body condition index (tail volume index) was only negatively correlated with urea, and triglyceride levels. A meta-analysis of available literature revealed a significant latitudinal relationship with PCV, TP, albumin, and triglycerides but this was confounded by variation in sampling times and restraint methods. We expand understanding of mainland platypuses, providing reference intervals for PCV and six blood chemistry, while highlighting the importance of considering seasonal variation, to guide future assessments of individual and population condition.

Impact of ageing on the response and repertoire of influenza virus-specific CD4 T cells

BACKGROUND

Ageing has been shown to reduce CD8 T cell repertoire diversity and immune responses against influenza virus infection in mice. In contrast, less is known about the impact of ageing on CD4 T cell repertoire diversity and immune response to influenza virus infection.

RESULTS

The CD4 T cell response was followed after infection of young and aged C57BL/6 mice with influenza virus using a tetramer specific for an immunodominant MHC class II epitope of the influenza virus nucleoprotein. The appearance of virus-specific CD4 T cells in the lung airways of aged mice was delayed compared to young mice, but the overall peak number and cytokine secretion profile of responding CD4 T cells was not greatly perturbed. In addition, the T cell repertoire of responding cells, determined using T cell receptor Vβ analysis, failed to show the profound effect of age we previously described for CD8 T cells. The reduced impact of age on influenza-specific CD4 T cells was consistent with a reduced effect of age on the overall CD4 compared with the CD8 T cell repertoire in specific pathogen free mice. Aged mice that were thymectomized as young adults showed an enhanced loss of the epitope-specific CD4 T cell response after influenza virus infection compared with age-matched sham-thymectomized mice, suggesting that a reduced repertoire can contribute to impaired responsiveness.

CONCLUSIONS

The diversity of the CD4 T cell repertoire and response to influenza virus is not as profoundly impaired by ageing in C57BL/6 mice as previously shown for CD8 T cells. However, adult thymectomy enhanced the impact of ageing on the response. Understanding the impact of ageing on CD4 T cell responses to influenza virus infection is an important prerequisite for developing better vaccines for the elderly.

Immunosenescence and immune response in organ transplantation

The immune system undergoes a complex and continuous remodeling with aging. Immunosenescence results into both quantitative and qualitative changes of specific cellular subpopulations that have major impact on allorecognition and alloresponse, and consequently on graft rejection and tolerance. Here, we are going to review the immunological changes associated with the aging process relevant for transplantation. Interventions to selectively target changes associated with the senescence process seem promising therapeutic strategies to improve transplantation outcome.

Immunosenescence and organ transplantation

Increasing numbers of elderly transplant recipients and a growing demand for organs from older donors impose pressing challenges on transplantation medicine. Continuous and complex modifications of the immune system in parallel to aging have a major impact on transplant outcome and organ quality. Both, altered alloimmune responses and increased immunogenicity of organs present risk factors for inferior patient and graft survival. Moreover, a growing body of knowledge on age-dependent modifications of allorecognition and alloimmune responses may require age-adapted immunosuppression and organ allocation. Here, we summarize relevant aspects of immunosenescence and their possible clinical impact on organ transplantation.

Potent early immune response after kidney transplantation in patients of the European senior transplant program

BACKGROUND

The increasing age of organ donors and the transplantation of older recipients have become clinical practice. Age-adapted immunosuppressive protocols considering these changes are currently not established. This study analyzed the age-dependent immune response after human kidney transplantation.

METHODS

One hundred renal allograft recipients were prospectively evaluated from 2004 to 2005. Patients older than 65 years of the European Senior Program receiving kidneys from donors older than 65 years were compared with recipients younger than 65 years receiving kidneys from donors younger than 65 years. Age-dependent modifications of the immune response were evaluated before transplantation and 7 days and 6 months after grafting by flow cytometry analysis of lymphocyte surface markers in peripheral blood. The cytokine pattern was determined by Cytometric Bead Array, T-cell alloreactivity by enzyme-linked immunospot analysis.

RESULTS

There were no differences between the groups regarding patient survival, graft survival, and function at 6 months after transplantation. Before transplantation, 7 days and 6 months thereafter recipients older than 65 years demonstrated significantly elevated numbers of memory T-cells while counts for naive T-cells were significantly reduced. Numbers of activated cytotoxic cells were elevated with increasing age before and 7 days after transplantation. T-cell alloreactivity was more pronounced in older recipients at all time points. Seven days after transplantation tumor necrosis factor-alpha (TNF-alpha) levels were significantly higher, whereas TNF-alpha and interleukin-10 (IL-10) concentrations were significantly reduced after 6 months in older recipients.

CONCLUSIONS

Our data demonstrate an initially pronounced immune response in elderly recipients receiving grafts from elderly donors. This observation supports the concept of a donor and recipient age-adapted immunosuppression.

Renal transplantation in the elderly

Elderly patients are increasingly being considered for kidney transplantation due to a global explosion of the aging population with end-stage renal disease (ESRD). However, mounting scarcity of available organs for transplant has led to a wider disparity between organ supply and demand. Consequently, the criteria for accepting kidneys for transplantation have been extended in an attempt to allow the use of organs from elderly donors or those with significant co-morbidities, so-called "expanded criteria donor" (ECD) kidneys. Excellent outcomes have been achieved from ECD kidneys with appropriate donor and recipient profiling and selection. With increasing recovery efforts directed at older donors, the concept of age-matching is becoming more accepted as a method of optimizing utilization of organs in elderly donors and recipients. Utilization of pulsatile perfusion has further improved ECD outcomes and helped the decision-making process for the UNOS (United Network for Organ Sharing) offer. However, age-related immune dysfunction and associated co-morbidities make the elderly transplant recipients ever more susceptible to complications associated with immunosuppressive agents. Consequently, the elderly population is at a higher risk to develop infections and malignancy in the post-transplant period notwithstanding improved transplant outcomes. Appropriate immunosuppressive agents and dosages should be selected to minimize adverse events while reducing the risk of acute rejections and maximizing patient and renal allograft survival.

Differential effects of age on circulating and splenic leukocyte populations in C57BL/6 and BALB/c male mice

BACKGROUND

Despite several reports on age-related phenotypic changes of the immune system's cells, studies that use a multipoint age comparison between the specific and innate immune cell populations of prototypical Th1- and Th2-type polarized mouse strains are still lacking.

RESULTS

Using a multipoint age comparison approach, cells from the two major immune system compartments, peripheral blood and spleen, and flow cytometry analysis, we found several principal differences in T cell and professional antigen presenting cell (APC) populations originating from a prototypical T helper (Th) 1 mouse strain, C57BL/6, and a prototypical Th2 strain, BALB/c. For example, regardless of age, there were strain differences in both peripheral blood mononuclear cells (PBMC) and spleens in the proportion of CD4+ (higher in the BALB/c strain), CD8+ T cells and CD11b+/CD11c+ APC (greater in C57BL/6 mice). Other differences were present only in PBMC (MHC class II + and CD19+ were greater in C57BL/6 mice) or differences were evident in the spleens but not in circulation (CD3+ T cells were greater in C57BL/6 mice). There were populations of cells that increased with age in PBMC and spleens of both strains (MHC class II+), decreased in the periphery and spleens of both strains (CD11b+) or did not change in the PBMC and spleens of both strains (CD8+). We also found strain and age differences in the distribution of naïve and memory/activated splenic T cells, e.g., BALB/c mice had more memory/activated and less naive CD8+ and CD4+ T cells and the C57BL/6 mice.

CONCLUSION

Our data provide important information on the principal differences, within the context of age, in T cell and professional APC populations between the prototypical Th1 mouse strain C57BL/6 and the prototypical Th2 strain BALB/c. Although the age-related changes that occur may be rather subtle, they may be very relevant in conditions of disease and stress. Importantly, our data indicate that age and strain should be considered in concert in the selection of appropriate mouse models for immunological research.

Age and immune response in organ transplantation

The immune system undergoes a complex and continuous remodeling as the result of aging. These changes have a major impact on allorecognition and alloresponse. In addition, immunosuppression in the elderly is challenging as a consequence of an increased incidence of associated comorbidities and altered pharmacokinetics. Both advanced donor and recipient age should be considered independent risk factors for poor patient and graft survival rates, albeit acting in a synergistic manner. Consequently, modifications of the immune system because of aging may request an age-adapted allocation and immunosuppression in parallel with close patient monitoring. Interventions to selectively target changes associated with the senescence process seem to be promising therapeutic strategies to improve transplantation outcome. Here, we are going to review the immunologic changes associated with the aging process relevant for transplantation and their impact on immunosuppressive protocols, organ allocation policies, and transplantation outcome.

Alterations of the immune response with increasing recipient age are associated with reduced long-term organ graft function of rat kidney allografts1

BACKGROUND

Clinically, an increasing number of older recipients are listed for transplantation. We examined recipient age-associated alterations of the immune response and their effects on graft function.

METHODS

Three- and 18-month-old Lewis (LEW) rats received kidneys from 3- and 18-month-old Fischer 344 (F344) rats (1.5 mg/kg/d cyclosporine A for 10 days; n=6/group) and were observed for 180 days. In additional groups, double kidney transplantations were performed to determine the impact of nephron mass and recipient age on graft outcome.

RESULTS

All young recipients but only 66% of old recipients survived the observation period. Increasing recipient age resulted in a significant decrease in renal allograft function (P<0.001), more advanced morphologic evidence of chronic allograft damage (P<0.001), and greater cellular infiltration (P<0.05) and major histocompatibility complex expression (P<0.01) within grafts. Additional in vitro studies examined age-related changes in the cellular immune response by enzyme-linked immunosorbent assay, fluorescence-activated cell sorter analysis, and alloreactive enzyme-linked immunospot: splenocytes from old LEW rats produced significantly more interleukin (IL)-2 (P<0.0001), IL-4 (P<0.05), interferon (IFN)-gamma (P<0.0001), and tumor necrosis factor-alpha (P<0.05). IFN-gamma-producing memory-type T cells were significantly elevated in older rats (P<0.0001). Moreover, they revealed significantly more alloreactive T cells directed against F344 (146 +/- 64.2 and 512 +/- 277/10(6) T cells; P<0.05). Double renal allografts from young donors into old recipients confirmed an independent effect of recipient age on the acceleration of chronic graft deterioration.

CONCLUSIONS

The enhanced cellular immune responsiveness in elderly recipients was associated with advanced chronic graft injury. Clinically, older recipients may need a modified immunosuppression.

Antigen-independent expansion of CD28hi CD8 cells from aged mice: cytokine requirements and signal transduction pathways

Memory CD8+ T cells from old mice can proliferate in nonirradiated recipients. Transfer of labeled cells from aged donors into young recipients showed that proliferation of aged donor CD8 cells requires host cells that can both respond to interferon-gamma and produce interleukin-15. Reisolation of transferred CD8 cells from host mice showed that LAT (linker for activated T cells) translocation to the immunological synapse, and translocation of NF (nuclear factor)-kappaB to the nucleus were diminished in recovered CD8 T cells from old donors, whether they had divided in vivo or not. Cells able to proliferate in vivo could be isolated based on their unusually high levels of CD28 expression, but were found not to differ from other aged CD8 cells in their low levels of LAT and protein kinase C-theta (PKC-theta) translocation to the immunological synapse. Thus in vivo proliferation of CD28hi CD8 cells from aged mice cannot be attributed to retention of T-cell receptor signaling.

Enhanced allostimulatory activity of host antigen-presenting cells in old mice intensifies acute graft-versus-host disease

Older bone marrow transplantation (BMT) recipients are at heightened risk for acute graft-versus-host disease (GVHD) after allogeneic BMT, but the causes of this association are poorly understood. Using well-characterized murine BMT models we have explored the mechanisms of increased GVHD in older mice. GVHD mortality, morbidity, and pathologic and biochemical indices were all worse in old recipients. Donor T cell responses were significantly increased in old recipients both in vivo and in vitro when stimulated by antigen-presenting cells (APCs) from old mice, which also secreted more TNF-alpha and IL-12 after LPS stimulation. In a B6 --> B6D2F1 model, CD4(+) donor T cells but not CD8(+) T cells mediated more severe GVHD in old mice. We confirmed the role of aged APCs in GVHD using B6D2F1 BM chimeras created with either old or young BM. Four months after chimera creation, allogeneic BMT from B6 donors caused significantly worse GVHD in old BM chimeras. APCs from these mice also stimulated greater responses from allogeneic cells in vitro. These data demonstrate a hitherto unsuspected mechanism of amplified donor T cell responses by aged allogeneic host APCs that increases acute GVHD in aged recipients in this BMT model.

HLA-A and HLA-B transcription decrease with ageing in peripheral blood leucocytes

Immunosenescence involves modifications of humoral and cellular immunity. In a previous study, we have shown a locus-dependent reduction of HLA class-I cell surface expression on peripheral lymphocytes and monocytes with advancing age. Here we report the quantitative analysis of HLA-A and -B transcripts from PBL of 54 healthy subjects aged 21-90 years. Using a competitive RT-PCR method, we observed a significant decrease of HLA-A (P < 0.0001) and -B (P = 0.0025) mRNA contents with increasing age. Secondly, to investigate this locus-dependent alteration of HLA class-I transcription, we performed EMSA using nuclear extracts from PBL of five young (24-31-year-old) and 5 elderly (58-69 years old) donors with locus A and B sequences of the Enh-A as probes. No qualitative variation of EMSA profiles appeared between the two groups of donors with 6 and 4 bandshift for the locus A and B, respectively. Quantitatively, we observed a significant increase of B4 intensity in the elderly group compared to the young group (P < 0.05). These results suggest that the variation of DNA binding protein could contribute to the lower transcription of HLA-A and -B with ageing. These alterations of HLA class-I expression at the transcriptional level could lead to the unresponsiveness of CD8 T cells due to default of antigen presentation with ageing.

Phenotypic and functional characteristics of circulating monocytes of elderly persons

Aging is associated with impairment of immune functions. Age-dependent alterations in T-cells are well known. Although the pivotal role of monocytes in immune regulation by their production of proinflammatory and inhibitory cytokines is acknowledged, limited information is available on monocyte changes in aging. The present study focused on phenotypic changes in circulating monocytes in elderly subjects and in the level of cytokines they produce. The results demonstrated a significant expansion of CD14dim/CD16bright circulating monocytes in elderly. In contrast, the majority of circulating monocytes of healthy young individuals were CD14bright/CD16dim. The CD14dim/CD16bright monocytes are considered to have phenotypic evidence for activation. Furthermore, significant increases of constitutive production of monocytic cytokines including interleukin (IL)-1beta. IL-1 receptor antagonist, and IL-6 by nonstimulated monocytes from elderly was also indicative of activation. This was also observed when monocytes from elderly were cultured with autologous lymphocytes. However, after stimulation, significantly lowered IL-1beta production was observed and IL-6 and IL-10 tended to be higher in the elderly. Collectively, these results indicate that monocytes of aged individuals, in contrast to a younger population exhibit in vivo activation as well as imbalanced production of cytokines. Such age-related alterations in monocytes may contribute to impaired immune competence of aging.

Cluster formation by protein kinase Ctheta during murine T cell activation: effect of age

Protein kinase Ctheta; (PKCtheta;) is thought to play an important role in T cell activation, in that exposure of cloned T cells to antigen-presenting cells bearing agonist peptides, but not antagonist peptides, leads to clustering of PKCtheta; molecules in the section of the T cell plasma membrane that is in contact with the APCs. To see whether aging affects this PKCtheta; clustering reaction in mouse T lymphocytes, we used immunofluorescence staining and confocal microscopy to observe the localization of PKCtheta; in CD4 and CD8 T lymphocytes activated by coincubation with anti-CD3 hybridoma cells. Aging led to a twofold decline in the proportion of both CD4 and CD8 T cells in which PKCtheta; underwent cluster formation. This decrease with age was not due to differences in the number of cell conjugates formed, nor to kinetic differences of PKCtheta; clustering, nor to the accumulation of memory T cells in old mice. There were no effects of aging on the levels or kinase activity of PKCtheta; in murine T cells. Our data suggest alterations in the upstream signals that regulate PKCtheta; translocation.

Chronic Modulation of the TCR Repertoire in the Lymphoid Periphery

Using TCR Vβ5 transgenic mice as a model system, we demonstrate that the induction of peripheral tolerance can mold the TCR repertoire throughout adult life. In these mice, three distinct populations of peripheral T cells are affected by chronic selective events in the lymphoid periphery. First, CD4+Vβ5+ T cells are deleted in the lymphoid periphery by superantigens encoded by mouse mammary tumor viruses-8 and -9 in an MHC class II-dependent manner. Second, mature CD8+Vβ5+ T cells transit through a CD8lowVβ5low deletional intermediate during tolerance induction by a process that depends upon neither mouse mammary tumor virus-encoded superantigens nor MHC class II expression. Third, a population of CD4−CD8−Vβ5+ T cells arises in the lymphoid periphery in an age-dependent manner. We analyzed the TCR Vα repertoire of each of these cellular compartments in both Vβ5 transgenic and nontransgenic C57BL/6 mice as a function of age. This analysis revealed age-related changes in the expression of Vα families among different cellular compartments, highlighting the dynamic state of the peripheral immune repertoire. Our work indicates that the chronic processes maintaining peripheral T cell tolerance can dramatically shape the available TCR repertoire.

Increased Zap-70 association with CD3zeta in CD4 T cells from old mice

Aging diminishes the amount of phosphotyrosine in the CD3zeta chains of resting and activated mouse CD4 T cells by about threefold and might therefore be expected to a corresponding decline in Zap-70 association with CD3zeta and in Zap-70 kinase function in CD3zeta complexes. We show here that aging leads, unexpectedly, to an approximately twofold increase in the amount of Zap-70 associated with CD3zeta in resting CD4 T cells. There is, however, no effect of age on total intracellular Zap-70 content. Cross-linking CD3 to CD4 leads to an increase of only 50% in the functional activity of Zap-70 in CD3zeta complexes from freshly isolated CD4 T cells of young donors. Compared to Jurkat and HT-2 cells, fresh T cells show both higher baseline levels and lower induced levels of Zap-70 function in CD3zeta complexes. CD4 T cells from old mice have baseline levels of Zap-70 activity similar to those seen in activated T cells from young mice, and these levels do not increase after CD3/CD4 cross-linking. Tyrosine-specific phosphorylation of Zap-70 is also higher at rest in old T cells than in young T cells and inducible only in cells from young donors. These data suggest that age-related defects in T cell activation are not likely to be attributable simply to a decline in Zap-70 association with CD3zeta or to diminished Zap-70 phosphorylation. The increase with age in CD3zeta-Zap association, despite the loss with age in CD3zeta tyrosine phosphorylation, suggests that the pattern of tyrosine phosphate groups among CD3zeta ITAM groups may be different in T cells from young and old donors or that access to ITAM regions within CD3zeta may be blocked by inter- or intramolecular steric hindrance in young CD4 T cells.

Modification of HLA expression on peripheral lymphocytes and monocytes during aging

Immunosenescence involves modifications of humoral and cellular immunity. Here we report the analysis of human leukocyte antigen (HLA) expression on T lymphocytes, B lymphocytes and monocytes of 58 healthy subjects aged 23-95 years old. Using a double staining immunofluorescence and flow cytometry analysis, we have determined the percentages of cells expressing HLA class-I and HLA-DR antigens. The number of antigenic sites expressed per cell were evaluated for HLA-ABCw, HLA-A, HLA-B, HLA-DR locus with a flow cytometry quantification technique. With advancing age, we observed: (i) a significant decrease of the percentage of T cells and B cells expressing HLA-A products; (ii) a decrease of the number of HLA class-I antigenic sites expressed per cell on the three populations tested, predominantly on B cells and in a locus-dependent fashion; (iii) a decrease of the number of HLA-DR molecules expressed per T cell, although the percentage of T cells expressing DR products was increased; (iv) a significant diminution of the percentage of B cells expressing HLA-DR molecules, without changes of the number of HLA-DR antigenic sites per cells. These changes in HLA expression with increasing age could contribute to the decreased level of immunologic responsiveness observed with ageing and contribute to the modification of antigen recognition.

Spontaneous autoimmune disease in (NZB x NZW)F1 mice is ameliorated by treatment with methimazole

(NZB x NZW)F1 mice spontaneously develop with age an autoimmune disease that resembles the human disease, systemic lupus erythematosus (SLE). The present study demonstrates that methimazole (MMI), an agent used in the treatment of autoimmune thyroid disease, is effective in mitigating the development of this SLE-like autoimmune disease in (NZB x NZW)F1 mice. MMI significantly reduces the incidence and severity of proteinuria and deposition of immune complexes in the kidney. Previous studies have demonstrated that development of an experimentally induced SLE, which was prevented by MMI treatment, depended on the expression of MHC class I molecules. We now report that class I levels on both T cells and B cells from old (NZB x NZW)F1 MHC class I are markedly elevated relative to those from young F1 mice. Furthermore, treatment of (NZB x NZW)F1 mice with MMI reduced MHC class I expression on their PBL concomitant with amelioration of disease, raising the possibility that class I molecules may play a role in the generation of spontaneous autoimmune disease in these mice.

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.

Anti-CD3-induced apoptosis in T-cells from young and old mice

Light scatter measurements using flow cytometry indicated that T cells from young and old mice undergo apoptosis following activation with immobilized anti-CD3. The percentage of cells in apoptosis after 20 h activation was significantly greater (p < .001) in cultures containing cells from older animals. The mean percentages of apoptotic T cells from young and old mice after 20 h activation were 19.3% and 33.0%, respectively. The proportion of viable cells after 20 h activation was significantly higher (p < .003) in the young (mean = 78.4%) than in the old animals (mean = 65.8%). Simultaneous measurements of light scatter and fluorescence indicated that apoptotic T cells contained both the CD4+ and the CD8+ T-cell phenotypes. The frequency of apoptotic CD8+ T cells was elevated (p < .007) in older animals, where the mean percentage was 15.1%, compared to 5.3% in the young. The most dramatic difference between young and old (p < .0008) was seen in the percentages of viable CD4+ T cells after 20 h activation. The mean viable CD4+ T-cell percentage was 33.7% in- the young and 21.4% in the old. CD4+ cells expressing high levels of CD45RB (CD45RBhi) after activation for 20 h possessed light scatter and bright fluorescence properties characteristic of viable cells, whereas CD4+/CD45RBlo density cells could be identified as apoptotic based on their decreased CD4 fluorescence and scatter characteristics. CD4+ cells from young animals were predominantly CD45RBhi, whereas CD4+ cells from the old had greater levels of CD454RBlo cells. In addition to light scatter changes, measurement of DNA content after 40 h activation revealed the presence of a sub-G1 DNA apoptotic peak and a viable cell cycle distribution. After 40 h of activation, there was an increase in the percentage of apoptotic cells in both young and old mice, with the greatest increase seen in the cells from older animals. Further evidence supporting the process of apoptosis in 40 h-activated cells was confirmed by the appearance of DNA strand breaks detected by in situ nick translation.

Physiological T-cell death: susceptibility is modulated by activation, aging, and transformation, but the mechanism is constant

It is not surprising that the recent explosion of interest in physiological cell death has been centered particularly on lymphocytes. Physiological cell death responses are singularly important in the biology of T lymphocytes, especially in the establishment and maintenance of a diverse, non-autoreactive, and self-limiting repertoire. Cell death responses can be triggered in T cells by a variety of stimuli; sensitivity to these inducers is altered as a function of differentiation, activation, aging, and transformation. The elimination of autoreactive T cells occurs by a process that involves comitogenic stimulation at high dose with antigenic and/or mitogenic agents. The control of susceptibility to this activation-driven cell death with differentiation and with prior activation provides a mechanistic explanation for the development of central and peripheral tolerance. Enhanced lymphocyte activation with aging also leads to an augmented activation-driven cell death response. However, aging does not alter cell death responses generally, and aging-associated changes in cell death responses cannot account for aging-associated immunopathology. Oncogenic transformation also alters the activation-driven cell death response by supplanting one of the required signals for activation-driven cell death. This difference provides a rationale for selective anti-tumor therapy. A single mechanism underlies all cases of physiological cell death and involves out-of-phase mitotic activity. We now know that of the two hallmarks of cell death, genome digestion is dispensable and mitotic-like events associated with cell cycle arrest are critical. T cells triggered to undergo physiological cell death arrest in a post-mitotic compartment of the cell cycle and die when they attempt a precocious and abortive mitosis.

Increased serum HLA class I molecule levels in elderly human responders to influenza vaccination

Increased cell surface expression and serum levels of HLA class I molecules have been shown to occur in normal elderly humans. Elderly subjects (65 years and older) generally also have a poorer response to influenza vaccine than younger adults. Some 30 to 40% of elderly subjects do not respond to influenza vaccination. Sera from 20 elderly subjects with a positive response to influenza vaccine (HAI antibody titer > 40) and 20 subjects who did not respond (HAI antibody titer < 40) were randomly selected and the levels of soluble HLA class I molecules determined before and after vaccination. The subjects who responded had higher serum HLA class I levels both before and after vaccination than did non-responders. Two weeks after vaccination non-responders showed similar serum HLA class I levels (1.78 mg/ml +/- 0.62) as compared to prevaccination levels (1.73 mg/ml +/- 0.49). The responders showed significantly higher levels of soluble HLA class I molecules following vaccination (2.64 mg/ml +/- 0.99) as compared to pre-vaccination (2.08 mg/ml +/- 0.85, p = 0.00001). Our results suggest that measuring soluble HLA class I molecules in the serum may be useful in assessing the adequacy of response to influenza vaccination in the elderly population.

Genes of the major histocompatibility complex and the evolutionary genetics of lifespan

Mice that presumably differ just in the major histocompatibility complex (MHC) chromosomal region provide the best evidence that MHC genes affect lifespan. Further evidence is that MHC region genes in some cases are known to influence reproduction, growth, and development. Moreover, MHC genetic associations with disease are well documented. This paper summarizes and defines aspects of the molecular biology, cellular function, and evolution of MHC genes (with special emphasis on the polymorphic MHC class I and II genes) which are important in aging, and attempts to integrate these into an evolutionary genetic perspective of senescence. It is suggested that MHC genes provide a mammalian paradigm for the genetics of lifespan because of their intra- and interspecies diversification, evolutionary selection, and age-specific effects.

Differential effect of aging on B-cell immune responses to cholera toxin in the inductive and effector sites of the mucosal immune system

The age-associated primary immune response of B cells from the Peyer's patches (PP), the lamina propria (LP), the mesenteric lymph nodes (MLN), and the spleen of mice following oral immunization with cholera toxin (CTx) was investigated. The induction of immune responses was assessed in 4-, 11-, and 24-month-old, individual C57BL/6J male mice by determining the number and isotype of anti-CTx ELISPOT-forming cells (SFC) in the PP, LPL, MLN, and spleen and the titer and isotype of serum anti-CTx antibody. The data indicate a significant age-associated decline in immunoglobulin G (IgG) and IgA anti-CTx SFC in the LP B cells but only in IgA anti-CTx SFC in the PP. No decline was seen in the anti-CTx SFC response in the MLN and spleen. Peroral immunization of mice with CTx resulted in a serum anti-CTx antibody response which was predominantly of the IgG class in all three age groups of mice tested. There was no age-associated decline in anti-CTx IgM, IgG, or IgA titers in serum. Isoelectric focusing and affinity immunoblotting revealed several distinct new antibody clonotypes in the immune serum of old mice following oral immunization with CTx. The results indicate a loss of immune responsiveness to CTx following oral immunization in senescent PP and LP B cells. The MLN and spleen B-cell responses were found to be refractory to the loss of immune function with aging. These findings suggest a differential effect of aging in the inductive and effector sites of the mucosal immune system, and the loss of antigen-specific IgA responses at mucosal sites may have adverse effects on the host's defense against potential pathogens.

T-cell function in aging: mechanisms of decline

The above sections have provided numerous facts, many of which are conflicting, regarding the changes that occur with increasing age in T lymphocytes. Although it is impossible to state with absolute certainty the alterations that are responsible for decreased proliferation of lymphocytes from elderly subjects, the following summarizes the current status of the data: 1. The interaction of T lymphocytes with foreign stimuli appears to be generally intact. 2. Changes in numbers of CD3+, CD4+, or CD8+ cells before interaction with foreign stimuli or in the density of these markers or of mitogen receptors on the surface of aged T cells have not been consistently observed. When reported to occur, the changes are not sufficient to account for the significant decrease in T-cell proliferation that occurs with increasing age. 3. A defect in the ability of the membrane interaction with foreign stimulus to signal subsequent internal events may occur, because stimulation with phorbol esters and calcium ionophore can result in increased proliferation in some elderly subjects. 4. Decreased accumulation of cytosolic calcium after stimulation of elderly T cells occurs in mice and may be a major component of the defective activation system. This defect appears to be most apparent in the "memory" T cells (T cells expressing high levels of Pgp-1), which increase in number with increasing age. Decreases in Ca++ accumulation have not been observed in humans, but this may be due to different stimuli used. Further, investigation of an increase in "memory" T cells and of their inability to mobilize Ca++ has not been done in humans and rats. 5. Decreases in mRNA for c-myc, IL-2 receptor, and IL-2 have been reported in some, but not all, species. Whether these decreases are the result of decreases in Ca++ mobilization or are independent events in unknown. 6. Decreases in membrane expression of the activation marker RL388 and of TfR have been reported. 7. Lymphokines: a. Decreases in IL-2 production occur in mice and humans, but not in rats. In individuals with decreased IL-2 production, addition of exogenous IL-2 totally restores proliferative ability in only some individuals. Changes in IL-2R expression (number or affinity) may be an additional defect. b. Decreases in IFN-gamma occur in humans, but not in mice or rats. c. No change in IL-1 occurs in any species. Genotypic effects must be considered when evaluating the preceding observations. The heterogeneity among individuals, even within an inbred strain, cannot be discounted.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging and immune function

Since it is too difficult to study aging of the organism as a whole, most investigators try to focus on a specific physiological system that exhibits age-dependent functional changes, in the hopes that elucidation (in biochemical and developmental terms) of the mechanism of senescent change will provide insight into the aging process itself. The immune system is among the most maleable of such models, in that well-defined cell types will produce well-defined molecules with predictable functions in vitro and in vivo. The increasing power of basic immunological science should, in the next decade, permit an increasingly fine appreciation of how aging leads to immune decline. This expanding conceptual framework will then suggest new ideas about the role of immunosenescence in degenerative, infectious, and neoplastic illnesses and may also generate increasingly rational strategies for therapeutic intervention.

Analysis of age-related degeneracy of T-cell repertoire: localized functional failure in CD8+ T cells

The repertoire and frequency of alloreactive T cells in aged mice were examined by limiting dilution analysis of the mixed-lymphocyte reaction (MLR). Mice were aged in specific pathogen-free conditions up to 31 months, and MLR of their spleen cells under limiting dilution conditions was examined at various stages of ageing. The frequency of alloreactive T cells was found to decrease in mice more than 14 months of age, and the value reached about 1/3 of that of young mice of 2 months of age. The slope analysis of cell dose-response curves of MLR indicated the existence of two interacting T-cell populations, i.e. CD4+ and CD8+, cooperation between which is required for the full manifestation of MLR in limiting dilution conditions. The decrease in the alloreactivity of aged spleen cells was ascribed to the selective functional loss of the CD8+ population, because the CD4+ but not the CD8+ T-cell fraction from aged mice could restore the limiting factor in MLR. The decrease in the cooperative activity of CD8+ T cells in allo-MLR starts much earlier than the decrease in the number of CD8+ T cells in the spleen.