Understanding the mechanism of the age-related decline in immune function

Assessment of Age-Related Decline of Immunological Function and Possible Methods for Immunological Restoration in Elderly

The immune system plays an important role in protection against infection and cancer, and in the maintenance of the internal environment of the body. However, such important immune functions are known to decline with age in many mammals, including humans. It is a matter of clinical importance that the incidence of various age-associated diseases such as infections, cancer, and vascular disorders increases with a decrease in immunological vigor. The extent of immunologic decline is variable and exhibits wide interindividual variations. Thus, it is important to assess the extent of immunologic decline in both patients suffering from various diseases and in healthy people in order to maintain healthy conditions. To this end, we have developed a scoring system that analyzes immune parameters according to a database of known age-associated immune changes obtained from a healthy population. Using this scoring system, we can combine several different immunological parameters and express the immune status of individuals as a simple numeral. Several methods of immunological restoration were introduced and the magnitude of restoration was evaluated by the quantitative assessment of immunological level.

Chronic retinal necrosis: cytomegalovirus necrotizing retinitis associated with panretinal vasculopathy in non-HIV patients

PURPOSE

To characterize a unique cytomegalovirus (CMV)-associated retinopathy in patients with limited immune dysfunction.

METHODS

Retrospective observational case series. CMV was confirmed as the pathogenic agent via polymerase chain reaction analysis of aqueous or vitreous humor samples or via immunohistochemical analysis of retinal biopsy specimens.

RESULTS

Five non-HIV patients with granular necrotizing retinitis, vitritis, and severe occlusive vasculopathy were identified. Patient histories all suggested a basis for limited immune dysfunction including advanced age (n = 4), diabetes mellitus (n = 4), and noncytotoxic immunotherapy (n = 3). Diagnosis of CMV retinitis was delayed in all cases and patients received either no antiviral therapy (n = 2) or incorrect antiviral therapy (n = 3) for presumed herpes simplex/varicella zoster-related acute retinal necrosis. Retinitis subsequently regressed in all cases with introduction of systemic ganciclovir/valganciclovir (n = 5) and/or intravitreal foscarnet (n = 2). Four of five patients developed neovascularization because of extensive retinal ischemia.

CONCLUSION

The clinical expression of CMV-associated retinopathy is strongly related to immune status. In patients with limited immune dysfunction, a mixed clinical picture of intraocular inflammation with panretinal occlusive vasculopathy, more characteristic of acute retinal necrosis, and peripheral slowly progressive granular retinitis, more characteristic of classic CMV retinitis, is observed. Recognition of this atypical clinical presentation, which the authors term chronic retinal necrosis, should prompt molecular testing for CMV to determine the appropriate antiviral therapy. Consideration should also be given to prophylactic panretinal photocoagulation in such eyes, given the high risk of neovascular complications.

Evaluating safety and efficacy of rabbit antithymocyte globulin induction in elderly kidney transplant recipients

OBJECTIVES

The optimal immunosuppression regimen for elderly kidney transplant recipients is poorly defined. We sought to evaluate the short-term efficacy and safety of thymoglobulin in geriatric recipients of deceased-donor kidneys.

MATERIALS AND METHODS

A single-center, retrospective analysis was undertaken between elderly (≥ 65 years) (n=137) and nonelderly (n=276) kidney transplant recipients who received rabbit antithymocyte globulin induction and calcineurin inhibitor, mycophenolic acid, and prednisone maintenance.

RESULTS

The mean age was 70 versus 52 years. Fewer elderly patients had an earlier transplant or panel reactive antibodies > 20%, but had more machine perfused, older, and extended criteria donor kidneys. Elderly patients received lower rabbit antithymocyte globulin (5.4 vs 5.6 mg/kg; P = .04) and initial mycophenolic acid doses (1620 vs 1774 mg; P = .002), and experienced less delayed graft function (31.1% vs 50.0%; P < .001). Death-censored graft survival and graft function at 3 years and biopsy-proven acute rejection at 1 year were comparable; however, there was lower 3-year patient survival in elderly patients. Donor age was the only factor associated with reduced patient survival. Rates of malignancy, infection, or thrombocytopenia were similar; however, leukopenia occurred less frequently in elderly patients (11.7% vs 19.9%; P = .038).

CONCLUSIONS

Elderly kidney transplant recipients receiving rabbit antithymocyte globulin did not experience different short-term graft survival, graft function or rates of infection, malignancy or hematologic adverse reactions than did nonelderly patients; they experienced fewer episodes of delayed graft function, but had lower 3-year patient survival.

High-dose immunoembolization: survival benefit in patients with hepatic metastases from uveal melanoma

PURPOSE

To retrospectively evaluate prognostic factors for survival in patients with uveal melanoma who received chemoembolization (CE) with 1,3-bis (2-chloroethyl)-1-nitrosourea or immunoembolization (IE) with granulocyte-macrophage colony-stimulating factor (GM-CSF) for hepatic metastases.

MATERIALS AND METHODS

Fifty-three consecutive patients with uveal melanoma were treated by using CE or IE in clinical trials approved by the Institutional Review Board. Prognostic factors associated with overall survival (OS) and progression-free survival (PFS) in the liver and extrahepatic (systemic) organs were retrospectively evaluated. Covariates of age, sex, preexisting extrahepatic metastases, liver enzyme levels, tumor volume, radiologic response in hepatic metastases, and treatment type were analyzed.

RESULTS

Compared with CE, high-dose (>or=1500 microg of GM-CSF) IE resulted in significantly better OS (20.4 vs 9.8 months, P = .005) and systemic PFS (12.4 vs 4.8 months, P = .001) at univariate analysis. Overall, women outlived men (14.4 vs 9.8 months, P = .01). Patients who achieved regression of hepatic metastases after embolization lived much longer than did those who did not achieve regression (27.2 vs 9.9 months, P < .001). At multivariate analysis, prolonged OS was confirmed for women, patients who underwent high-dose IE, younger patients (age < 60 years), and patients with regression of hepatic metastases. Independent predictors of longer systemic PFS included high-dose IE, younger age, and regression of hepatic metastases. No covariate predicted liver PFS except for hepatic response.

CONCLUSION

Treatment with high-dose IE prolonged survival of patients with uveal melanoma who received embolization of hepatic metastases and possibly delayed progression of extrahepatic metastases.

BONE MARROW, THYMUS AND BLOOD: CHANGES ACROSS THE LIFESPAN

The aim of this review is to present age-related changes in the bone marrow and thymus and their effects in later life. Age-related hematologic changes are marked by a decline in marrow cellularity, increased risk of myeloproliferative disorders and anemia, and a decline in adaptive immunity. The exact mechanisms that produce these changes remain undefined. For the most part, the changes in function that are a consequence of aging alone rarely have meaningful clinical consequences. However, in the face of the stresses induced by other illnesses, the decreased physiologic reserve can slow or prevent an appropriate response to the stressors.

Assessment of Age-related Decline of Immunological Function and Possible Methods for Immunological Restoration in Elderly

The immune system plays an important role in protection against infection and in the maintenance of the internal environment of the body. However, such important immune functions are known to decline with age in many mammals, including humans. It is a matter of clinical importance that the incidence of various age-associated diseases such as infections, cancer and vascular disorders increases with a decrease in immunological vigor. The extent of immunologic decline is variable and exhibits wide inter-individual variations. Thus, it is important to assess the extent of immunologic decline in both patients suffering from various diseases and in healthy people in order to maintain healthy conditions. To this end, we have developed a scoring system that analyzes immune parameters according to a database of known age-associated immune changes obtained from a healthy population. Using this scoring system, we can combine several different immunological parameters and express the immune status of individuals as a simple numeral.

After determining immunological vigor for individuals, it is necessary to replenish immune defects and restore them to normalcy for individuals with depressed immunological scores. This chapter provides methods of immunological restoration in animal models and introduces some similar attempts in humans. The effect of any immunological restoration varies with the individual and must therefore verified. Currently, the proposed immune scoring system proposed is useful to determine whether the methods employed are effective for the restoration of immune functions.

Physical activity and cancer prevention : pathways and targets for intervention

The prevalence of obesity, an established epidemiological risk factor for many cancers, has risen steadily for the past several decades in the US and many other countries. Particularly alarming are the increasing rates of obesity among children, portending continuing increases in the rates of obesity and obesity-related cancers for many years to come. Modulation of energy balance, via increased physical activity, has been shown in numerous comprehensive epidemiological reviews to reduce cancer risk. Unfortunately, the effects and mechanistic targets of physical activity interventions on the carcinogenesis process have not been thoroughly characterized. Studies to date suggest that exercise can exert its cancer-preventive effects at many stages during the process of carcinogenesis, including both tumour initiation and progression. As discussed in this review, exercise may be altering tumour initiation events by modifying carcinogen activation, specifically by enhancing the cytochrome P450 system and by enhancing selective enzymes in the carcinogen detoxification pathway, including, but not limited to, glutathione-S-transferases. Furthermore, exercise may reduce oxidative damage by increasing a variety of anti-oxidant enzymes, enhancing DNA repair systems and improving intracellular protein repair systems. In addition to altering processes related to tumour initiation, exercise may also exert a cancer-preventive effect by dampening the processes involved in the promotion and progression stages of carcinogenesis, including scavenging reactive oxygen species (ROS); altering cell proliferation, apoptosis and differentiation; decreasing inflammation; enhancing immune function; and suppressing angiogenesis. A paucity of data exists as to whether exercise may be working as an anti-promotion strategy via altering ROS in initiated or preneoplastic models; therefore, no conclusions can be made about this possible mechanism. The studies directly examining cell proliferation and apoptosis have shown that exercise can enhance both processes, which is difficult to interpret in the context of carcinogenesis. Studies examining the relationship between exercise and chronic inflammation suggest that exercise may reduce pro-inflammatory mediators and reduce the state of low-grade, chronic inflammation. Additionally, exercise has been shown to enhance components of the innate immune response (i.e. macrophage and natural killer cell function). Finally, only a limited number of studies have explored the relationship between exercise and angiogenesis; therefore, no conclusions can be made currently about the role of exercise in the angiogenesis process as it relates to tumour progression. In summary, exercise can alter biological processes that contribute to both anti-initiation and anti-progression events in the carcinogenesis process. However, more sophisticated, detailed studies are needed to examine each of the potential mechanisms contributing to an exercise-induced decrease in carcinogenesis in order to determine the minimum dose, duration and frequency of exercise needed to yield significant cancer-preventive effects, and whether exercise can be used prescriptively to reverse the obesity-induced physiological changes that increase cancer risk.

Combination of physical activity, nutrition, or other metabolic factors and vaccine response

A number of lifestyle factors that reduce cancer risk in the primary prevention setting may be potential new targets for use in combination with cancer vaccines. This review discusses the modulation of energy balance (physical activity, calorie restriction, and obesity prevention), and the supplementation with natural and synthetic analogs of vitamins A and E, as potential interventions for use in combination with cancer vaccines. Additionally, the pharmacologic manipulation of nutrient metabolism in the tumor microenvironment (e.g., arachidonic acid, arginine, tryptophan, and glucose metabolism) is discussed. This review includes a brief overview of the role of each agent in primary cancer prevention; outlines the effects of these agents on immune function, specifically adaptive and/or anti-tumor immune mechanisms, when known; and discusses the potential use of these interventions in combination with therapeutic cancer vaccines. Modulation of energy balance through exercise and strategies targeting nutrient metabolism in the tumor microenvironment represent the most promising interventions to partner with therapeutic cancer vaccines. Additionally, the use of vitamin E succinate and the retinoid X receptor-directed rexinoids in combination with cancer vaccines offer promise. In summary, a number of energy balance- and nutrition-related interventions are viable candidates for further study in combination with cancer vaccines.

Cancer and aging: symposium of the 27th annual meeting of the Japanese society for biomedical gerontology, Tokyo

Although many hypotheses have been proposed to explain the strong link between aging and cancer, the exact mechanisms responsible for the increased frequency of occurrence of cancer with advancing age have not been fully defined. Recent evidence indicates that malregulation of the apoptotic process may be involved in some aging process as well as in the development of cancer. Although it is still under debate how apoptosis is expressed during aging in vivo, this phenomenon is an important factor in unwinding the complicated mechanisms that link cancer and aging. In this review, we report on the discussion at the symposium of the 27th annual meeting of the Japanese society for biomedical gerontology, regarding recent findings from aging and carcinogenesis studies using animal models, the characteristics of cancer in patients with Werner's syndrome, the epigenetic changes in human cancers and aging, and the characteristics of human cancers in the elderly. It was concluded that apoptosis plays a role in the aging process and carcinogenesis in vivo, likely as an inherent protective mechanism against various kinds of damages to genes/chromosomes.

Effects of Maharishi Amrit Kalash 5 as an Ayurvedic herbal food supplement on immune functions in aged mice

Background

Maharishi Amrit Kalash (MAK) 5, one of the Ayurvedic food supplements, belongs to a group of substances known as Rasayana. MAK5 and other Rasayanas are believed to enhance the body's resistance to infections and disease, and enhance longevity. In this study, we determined the effects of administration of MAK5, one of the Ayurvedic food supplements on immune functions in young and old mice.

Methods

Male C3H/He N mice were divided into five groups: two no treatment groups (old control: 22-month-old and young control: 2-month-old) and three MAK5 treated groups with differing dose of MAK5. MAK5 was given p.o. at 50 mg/kg, 100 mg/kg or 200 mg/kg per day (3 days/week) for 2 months.

Results

We found that glucose consumption of peritoneal macrophages from old mice treated with MAK5 at all doses and incubated for 48 and 72 h were significantly greater than that in the control group. Nitric oxide production of peritoneal macrophages stimulated by lipopolysaccharide (LPS) in old mice treated with MAK5 at all doses was significantly greater than that in the old control group, but not compared to the young control group. Stimulation index (S.I.) in old mice gavaged with MAK5 at all doses was significantly higher than that in the old control group. IL-2 production stimulated by Con A in old mice given MAK5 at all doses was significantly higher than that in the old control group. Production of IFN-γ stimulated by Con A in old mice given MAK5 at doses of 100 mg/kg and 200 mg/kg were significantly higher than that in the old control group. IL-4 production of splenic lymphocyte stimulated by Con A in old mice given MAK5 at dose levels of 100 and 200 mg/kg were significantly higher than that in the old control group.

Conclusion

The results suggest that MAK5 suppressed the age associated glucose consumption of peritoneal macrophages and cellular immune function reduction, and that it contributes to the prevention of the immunosenescence.

Influence of age and physical activity on the primary in vivo antibody and T cell-mediated responses in men

The aging immune system is characterized by the progressive decline in the antibody and T cell-mediated responses to antigen. Little is known, however, about the benefits of exercise in aging on the generation of a primary immune response to antigen and the subsequent antibody and memory T cell-mediated response. Most in vivo immune research to date has utilized vaccines or recall antigens to elicit an immune response. Therefore, the purpose of this experiment was to examine the association of aging and physical activity on the primary antibody and T cell response to the novel protein antigen keyhole-limpet hemocyanin (KLH). Forty-six physically active and sedentary, young (20-35 yr) and older (60-79 yr) men were recruited. Subjects were intramuscularly immunized with 100 microg of KLH, and blood samples were collected at days 0, 7, 14, 21, and 28. Samples were measured for anti-KLH IgM, IgG, IgG1, and IgG2 by ELISA. On day 21 after intramuscular KLH administration, subjects received an intradermal injection with 1 microg of KLH of inflammation recorded at 24, 48, 72, 96, and 120 h to assess anti-KLH delayed-type hypersensitivity response. There was a significant reduction in all anti-KLH measures with aging except for anti-KLH IgG2. The physically active older group had significantly higher anti-KLH IgM, IgG, IgG1, and delayed-type hypersensitivity responses, but not IgG2 compared with the sedentary older group. In conclusion, regular physical activity in older men is associated with a more robust immune response to novel antigenic challenge.

Ovarian Cell-Mediated Immune Response to Salmonella enteritidis Infection in Laying Hens (Gallus Domesticus)

The aim of this study was to examine the response of cell-mediated ovarian immunity against Salmonella infection in hens. Laying hens were injected intraperitoneally with PBS (control) or Salmonella enteritidis (SE). Ovarian stroma containing stromal follicles, small white follicles (SWF), and third largest (F3) and the largest (F1) follicles were collected 12 or 24 h after inoculation and fixed in periodate-lysine-paraformaldehyde. Frozen sections were stained first for CD3+, CD4+, or CD8+ T cells and then for SE by a double immunostaining method. Immunoreaction products for SE were detected in the ovarian stroma, theca of stromal follicles, SWF, F3, and F1 at 12 and 24 h after inoculation. Immunopositive T-cell subsets were localized in the stroma and theca of follicles in birds inoculated with or without SE. The populations of CD3+, CD4+, and CD8+ T cells were significantly greater in the stroma and the theca of follicles 12 h after SE inoculation than in those of control birds (P < 0.01). Their frequencies were further increased in those tissues 24 h after inoculation (P < 0.01). Injection of SE did not cause significant differences in the CD4+:CD8+ T-cell ratio as both subsets increased proportionately. The current results indicate that the population of T-cell subsets increases in the ovarian stroma and the follicular tissues in response to SE invasion within 12 h of inoculation. Thus, cell-mediated immune response against SE, their products, or both may be induced in the hen ovary.

Involvement of growth factors in thymic involution

The thymus undergoes an age-dependent degenerative process which is mainly characterized by a progressive loss of lymphoid tissue. Thymic involution is particularly important in relation to immunosenescence and its various associated diseases; this fact has prompted many studies aimed at understanding the causes and mechanisms of thymic degeneration which may, ultimately, lead to the possibility of manipulating it. In this sense, one of the aspects which has deserved most attention is the thymic microenvironment, and more precisely, the many growth factors to which the cells present in the organ are exposed. Thus, the levels of several of such factors have been reported to undergo age-dependent changes in the thymus, which may point at an influence on the regression of the organ. In this article we consider which growth factors and growth factor receptors occur in the vertebrate thymus. Then, focusing on those whose influences are better documented, i.e., neurotrophins, cytokines and IGFs, we discuss their potential role in the organ and the possibility of their being involved in thymic involution.

Thymic generation and regeneration

The thymus is a complex epithelial organ in which thymocyte development is dependent upon the sequential contribution of morphologically and phenotypically distinct stromal cell compartments. It is these microenvironments that provide the unique combination of cellular interactions, cytokines, and chemokines to induce thymocyte precursors to undergo a differentiation program that leads to the generation of functional T cells. Despite the indispensable role of thymic epithelium in the generation of T cells, the mediators of this process and the differentiation pathway undertaken by the primordial thymic epithelial cells are not well defined. There is a lack of lineage-specific cell-surface-associated markers, which are needed to characterize putative thymic epithelial stem cell populations. This review explores the role of thymic stromal cells in T-cell development and thymic organogenesis, as well as the molecular signals that contribute to the growth and expansion of primordial thymic epithelial cells. It highlights recent advances in these areas, which have allowed for a lineage relationship amongst thymic epithelial cell subsets to be proposed. While many fundamental questions remain to be addressed, collectively these works have broadened our understanding of how the thymic epithelium becomes specialized in the ability to support thymocyte differentiation. They should also facilitate the development of novel, rationally based therapeutic strategies for the regeneration and manipulation of thymic function in the treatment of many clinical conditions in which defective T cells have an important etiological role.

Seasonal changes in the physiology of male Virginia opossums (Didelphis virginiana): signs of the Dasyurid semelparity syndrome?

Semelparity, which is multiplying once in a lifetime, is a rare reproductive strategy among mammals. Several species of the marsupial family Dasyuridae experience 100% male mortality following an intense mating period. We investigated seasonal physiological changes that may be associated with early mortality in the male Virginia opossum (Didelphis virginiana; Didelphidae) and compared these changes with those of semelparous, male dasyurids. Free-ranging male Virginia opossums (n=36) were collected during 2001 at the Oklahoma State University Cross Timbers Experimental Range. Seasonal data were collected on hematological, morphological, and helminth parameters of these individuals. We used one-way ANOVA to determine whether there were seasonal differences among means for each parameter. It appeared that male Virginia opossums experienced some physiological changes similar to those of male dasyurids exhibiting semelparity. All males collected in summer (August) were juveniles of the year. Lack of adult males in August suggests high mortality of this cohort during the breeding season. Opossum characteristics exhibiting the dasyurid semelparity syndrome included packed cell volume, adrenal mass, and helminth numbers. Minor lymphocytopenia, neutrophilia, and testosterone concentrations also were similar to semelparous dasyurids. However, a lack of change in serum cortisol concentration and body mass and dynamics in immunoglobulin protein, serum protein, and testes mass were not consistent with previous reports of semelparous dasyurid physiology. Evolutionary divergence and differences in breeding behavior between dasyurids and didelphids may be responsible for the lack of consistency between the taxa.

Kidney transplantation in older patients: benefits and risks

The proportion of older patients accepted for dialysis is increasing every year both in the US and abroad. Of the two treatment modalities for end-stage renal disease, i.e. dialysis and transplantation, the latter offers more freedom and is associated with better clinical outcome. Most elderly patients seem to have excellent functional rehabilitation after a kidney transplant. However, in view of the wide gap between the availability of cadaver organs and the people in need, giving the precious organ to the elderly who have a shorter expected lifespan may present an ethical problem. Therefore, it has become increasingly important to offer the kidney to only those who have no significant comorbid conditions or other high risk factors, so as to improve the odds of success after renal transplantation.

Age-related quantitative alterations in lymphocyte subsets and immunoglobulin isotypes in healthy horses

OBJECTIVE

To characterize age-associated changes in lymphocyte population subsets and immunoglobulin isotypes.

ANIMALS

30 healthy young light-breed horses (5 to 12 years old) and 30 healthy aged light-breed horses (> 20 years old).

PROCEDURE

Lymphocyte subset populations were identified, using monoclonal antibodies to cell surface markers CD5, CD4, CD8, and IgG. Subset populations were quantitated by use of flow cytometric analysis of antibody-stained cells. Serum immunoglobulin concentration was determined using single radial immunodiffusion.

RESULTS

Absolute cell counts of total lymphocytes, T cells, CD4+ and CD8+ T cells, and B cells were decreased in aged horses, compared with young horses. There was a significant decrease in the percentage of CD8+ cells and an increase in the CD4+-to-CD8+ cell ratio in the aged population, compared with young horses. However, serum concentration of IgG, IgG(T), IgM, or IgA did not differ with age.

CONCLUSIONS AND CLINICAL RELEVANCE

In horses, total lymphocyte count and lymphocyte subset cell counts decrease with age. Age-matched control values are necessary for optimal evaluation of hematologic variables in aged horses. The decrease in lymphocyte subset cell counts in healthy aged horses mimics that seen in other species and may contribute to an age-associated decrease in immunocompetency.

Role of lymphoid cells in age-related change of susceptibility to Friend leukemia virus-induced leukemia

Susceptibility for Friend leukemia virus (FLV)-induced leukemogenesis was examined in the C3H/He (C3H)-->C57BL/6 (B6) radiation bone marrow chimeras of various age groups, and the effect of aging of host mice on the susceptibility was determined. The bone marrow chimera system provided the various age of FLV-resistant host mice (B6) possessing the same age of FLV-susceptible target cells from C3H mice. Using this system, we could determine the aging effect on the host resistancy against FLV without an influence of the aging effect on target cells. First, the young C3H-->young B6 chimeras and young C3H-->old B6 chimeras were compared. The young-->old chimeras were more susceptible to FLV-induced acute disease than the young-->young chimeras. The spleen CD4+ as well as CD8+ T cells were reduced in young-->old chimeras compared with young-->young chimeras. Similarly, the old C3H-->old B6 chimeras were more susceptible than old-->young chimeras and revealed the lower CD4+ T cell ratio in the spleen. Discussion was made on the possible implication of these findings on the role of T cells in age-related change of resistance to FLV-induced leukemogenesis.

The immune system in the elderly: I. Specific humoral immunity

Profound and complex changes in the immune response occur during the aging process. Immunosenescence is reflected by a sum of disregulations of the immune system and its interaction with other systems. Many of the changes would appear to implicate age-related deficiencies of the immune responses. The term immunosenescence designates therefore a sort of deterioration of the immune function which is believed to manifest itself in the increased susceptibility to cancer, autoimmune disease, and infectious disease. Evidence has been accumulating from several studies which suggest an association between immune function and individual longevity. However, there are observations, especially in very old healthy people, that several immune functions are unexpectedly well preserved and substantially comparable to those observed in young subjects. These findings raise the question of whether the alterations that can be observed in the immune parameters of the elderly are a cause or a result of underlying disease processes. Moreover, studies on centenarians revealed a remodeling of the immune system rather than a deterioration, suggesting that the changes observed during immunosenescence do not correspond to immunodeficiency. The underlying mechanisms of these events are however still unclear. The purpose of the present review is to assess the status of research on the immunobiology of aging. In this first section, we focus attention on the B cell biology of aging. In clinical practice, the changes in humoral immune responsiveness and antibody-mediated defense mechanisms could greatly influence the incidence and outcome of bacterial infections and autoimmune diseases as well as the response to vaccines.

Age- and disease-related decline in immune function: an opportunity for "thymus-boosting" therapies

The thymus is the site of production of mature T lymphocytes and thus is indispensable for the development and maintenance of the T cell-mediated arm of the immune system. Thymic production of mature T cells is critically dependent on an influx of bone marrow-derived progenitor T cells that undergo replication and selection within the thymus. Thymus cellularity and thymic hormone secretion reach a peak during the first year of life and then decline gradually until the age of 50-60 years, a process known as "thymic involution." A rapid reduction of thymus cellularity occurs in young patients following injuries, chemotherapy, and other forms of stress. The mechanisms underlying the involution process appear to be dependent on factors intrinsic to the thymic tissue, such as the local production of cytokines and chemoattractants, promoting the recruitment, growth, and differentiation of bone marrow-derived T cell progenitors in the thymus, as well as extrinsic factors, such as systemic levels of endocrine hormones and mediators released by intrathymic nerves of the autonomic nervous system. Knowledge of these factors provides a rational basis for the development of an approach based on tissue engineering that could be used to provide either temporary or permanent reconstitution of thymic function.

Immunological changes in the elderly

Immunosenescence is a complex remodelling of the immune system which may contribute significantly to morbidity and mortality in the elderly. Much evidence suggests an association between immune function and longevity. It was advanced that individuals who have survived in good health to the maximum life span are equipped with optimal cell defense mechanisms. Despite the great number of studies on the immune system in the elderly, little is known of the biological basis of immunosenescence in humans. This is partly due to the contrasting results often obtained by the various investigators. One source of discrepancy is that diseases are frequent in aging, and the alterations observed in the immune parameters of the elderly could be a cause or alternatively a consequence of the underlying pathological processes. Undoubtedly some diseases to which aged people are particularly susceptible, such as infectious, autoimmune and neoplastic pathologies, include dysregulation of several immune functions in their pathogenesis. On the other hand, recent studies in healthy centenarians suggest that the immunological changes observed during aging are consistent with a reshaping, rather than a generalized deterioration, of the main immune functions. Considering that the number of old people is dramatically increasing, and that geriatric pathology is becoming an important aspect of clinical practice, it seems particularly interesting to review the peculiar findings in the immune system of the elderly so as to better understand their susceptibility to certain diseases, and the links between health and longevity.

Effects of aging and sex steroids on the localization of T cell subsets in the ovary of chicken, Gallus domesticus

The goal of this study was to determine the effects of aging and sex steroids on the frequency of T cells in hen ovary. Cryostat sections of ovarian tissues of immature and laying hens and those of immature hens treated with or without diethylstilbestrol (DES) or progesterone were immunostained for T cells using mouse anti-chicken CD3 (antigen of mature T cells), CD4 (antigen of helper T cells), and CD8 (antigen of cytotoxic T cells) monoclonal antibodies. Positive cells were observed under a light microscope and counted using a computer-assisted image analyzer. The frequency of CD3(+), CD4(+), and CD8(+) cells in the ovarian stroma and theca of primary follicles was significantly greater in young laying hens than in immature and old laying hens (P < 0.01). The CD4:CD8 ratio was significantly higher in the ovarian stroma of old laying hens than that of immature hens (P < 0.01), which was due to a greater decrease of CD8(+) cells than of CD4(+) cells. The frequency of CD3(+), CD4(+), and CD8(+) cells was significantly greater in the stroma and theca of primary follicles of DES-treated birds than in those of progesterone-treated and control birds (P < 0.01). Progesterone had no significant effect on the population of each subset of T cells. These results suggest that T cell frequency increases in association with sexual maturation and decreases thereafter during aging with an increase of CD4:CD8 ratio. Also, it is likely that estrogen is one of the factors which stimulates the influx of T cells in the hen ovary.

Perioperative cytokine release during coronary artery bypass grafting in patients of different ages

Surgical interventions and cardiopulmonary bypass (CPB) induce a systemic inflammatory response with cytokine release. Ageing is perceived as a process of impaired immune functions: IL-1beta, IL-6 and tumour necrosis factor-alpha (TNF-alpha) secretion are increased while IL-2 release is reduced in advanced age. At present, little information is available about perioperative immune reactions at different stages of ageing. The aim of the present study was to compare IL-6, IL-1beta, TNF-alpha, IL-10 and soluble IL-2 receptor (sIL-2R) in younger and older patients undergoing cardiac surgery. Male patients (n = 14) undergoing elective coronary artery bypass grafting (CABG) surgery employing CPB with moderate hypothermia were divided into two groups according to their age: group 1 included seven patients < 50 years old, group 2 included seven patients > 65 years old. All patients received general anaesthesia using a balanced technique with sufentanil, isoflurane and midazolam. Blood samples were collected pre-operatively (T1); intra-operatively during CPB (T2); post-operatively on the day of surgery (T3); on the first post-operative day (T4). Blood concentrations of IL-6, IL-1beta, IL-10, TNF-alpha and sIL-2R were measured using commercially available ELISA kits and corrected for plasma cell volume. Statistical analysis was performed by non-parametric analysis of variance and Mann-Whitney U-test. Significance level was set to P<0.05. There were no statistically significant differences in the perioperative release of TNF-alpha, IL-6, IL-1beta, IL-10 and sIL-2R among the two groups. We conclude that the perioperative course of cytokine release in patients undergoing CABG surgery with CPB and comparable perioperative management does not significantly differ in the two age groups.

Autoantibodies to T-lineage cells in aged mice

Aging is accompanied by a marked decline in protective immune function. This loss of effective immunity is largely due to alterations in the T-cell compartment. There are major impairments in both the production of new T-cells within the thymus and in the functions of mature T-cells in peripheral lymphoid organs. The mechanism(s) underlying this age-related decline in T-lineage cells is not clear. Here, we demonstrate that aging is accompanied by the appearance of appreciable titers of anti-T-lineage autoantibodies. The autoantibodies, which are exclusively of the IgM class, begin to appear at 1 year of life and are universally found in the sera of 2-year-old mice. Among thymocytes, all CD4/CD8 subsets reacted with the autoantibodies, with the CD4+8+ subset showing the greatest reactivity. The autoantibodies also bound to resting peripheral CD4+ and CD8+ cells. Following activation with either anti-CD3 or with TCR-independent stimulators, reactivity to peripheral T-cells was diminished, suggesting that the determinants recognized by the autoantibodies are downregulated in response to activation signals. Lastly, thymocytes freshly isolated from old, but not young, mice have IgM antibodies bound to their surfaces. Thus, circulating autoantibodies in old mice have access to the thymus and bind to thymocytes in situ. These results lead to the proposal that the presence of anti-T-lineage autoantibodies in vivo interferes with normal T-cell development and/or function in aged animals.

Hypothalamic control of development and aging of the thymus

Removal of pituitary gland results in atrophy of the thymus. As the pituitary gland is under the control of the hypothalamus, destruction of the anterior portion of the hypothalamus (AHTL) is expected to negatively influence the thymic function. Contrary to our expectation, the thymus became hypertrophic and the serum level of the growth hormone (GH) markedly increased, when the anterior portion of the hypothalamus was widely destroyed in rats at 1 month and over. The results suggested that AHTL removed the cells secreting GHRIH (growth hormone release inhibitory hormone), but not GHRH (growth hormone releasing hormone), leading to increased secretion of GH from pituitary gland and thymic hyperplasia. In other words, the development and aging of thymus appears to be under the balance of the positive (GHRH) and negative (GHRIH) signals of the hypothalamus. It is most likely that the positive signal is high just after the birth and decreases thereafter with a concomitant increase of the negative signal, leading to the onset of thymic atrophy at around puberty.

From naive to effector--alterations with aging

We have used a T-cell receptor transgenic mouse model to study the role of antigen in the changes that occur as T cells age. We find that the characteristic shift in the CD4 population to a predominance of memory phenotype T cells which accompanies aging in non-transgenic mice does not occur, suggesting that this shift is a result of antigenic stimulation. Thus at least one component of aging must be antigen dependent. When responses of naive CD4 T cells from aged and young mice are directly compared in vitro, the former are relatively deficient in their ability to produce IL-2 and IL-3, they express altered levels of P-glycoprotein and they proliferate less well in the absence of exogenous cytokines. When the ability of both naive populations to generate effectors is compared, the number of effectors generated from aged naive cells is much reduced and the effectors generated express lower levels of IL-2R alpha and produce reduced levels of cytokines. Importantly, addition of IL-2 restores proliferation of aged naive T cells, restores efficient effector generation and results in effectors seemingly indistinguishable from those derived from young CD4 cells. Similar phenotypic and functional changes seen with aging are also found in T-cell populations from IL-2 and IL-2R alpha knockout mice. Thus the loss of optimal IL-2 production may participate in the aging process and may represent the main antigen-independent defect in the CD4 T-cell population.

Thymocyte development in vitro: implications for studies of ageing and thymic involution

Functional defects that accumulate in the T cell compartment are thought to be responsible for the pronounced immunodeficiency that develops during ageing, and reduced production of T cells by the thymus as it undergoes involution has been suggested to contribute to this phenomenon. Understanding the mechanisms responsible for thymic involution requires a thorough knowledge of how thymopoiesis is regulated. Obtaining such information is dependent upon the availability of defined experimental systems that permit analysis of thymopoiesis at the cellular and molecular levels. Recent advances have been made in the development of such human and murine in vitro systems, and their analysis has the potential to identify thymic microenvironmental signals that regulate T cell production. This information should, in turn, provide a basis for understanding changes in thymopoiesis that occur during ageing. The features of these culture systems are reviewed in this article, and their potential application to the study of T cell production during ageing is discussed.

Reversing and restoring immune functions

Restoration of immunological functions is keenly needed for the improvement of quality of life of the elderly as the elderly population is rapidly increasing throughout the world. A brief review was made on the methods to restore or reverse immunological functions in the aged human and animals, including those presented in the Mini-Symposium at the 1st International Conference on Immunology and Aging. The methods discussed were (1) grafting of cells and tissues, (2) dietary manipulation, (3) free radical scavengers or anti-oxidants, (4) thymic peptides, (5) endocrine manipulation and (6) physical exercise. There is no easy and simple method for immunological restoration, as people are variable in terms of genetics, habit and culture. We need comprehensive study to test the effect of combination of a few or several methods for immunological restoration.

Time to systemic metastases in patients with posterior uveal melanoma

A total of 116 patients, all of whom had systemic metastases from posterior uveal melanoma, were evaluated to identify potential indicators for time to systemic metastasis. In the multivariate Cox proportional hazards model with clinically available variables, the age at initial treatment for uveal melanoma, gender and diameter of the primary tumor were revealed to be independent predictive factors for time to systemic metastasis. Age older than 60 years, male gender, and diameter of the primary uveal melanoma more than 10 mm were proved to be independent unfavorable factors. The estimated median time to systemic metastasis for the most unfavorable group (age > 60, male, diameter > 10 mm) was 20.2 months in contrast with 76.1 months for the most favorable group (age < or = 60, female, diameter < or = 10 mm). Although the results of this study cannot be applied to all patients with posterior uveal melanoma, predictive factors for time to systemic metastasis in those patients who have recurred supplement the information obtained from prognostic factors for the likelihood of metastasis or survival. They contribute not only to our understanding of the biology of metastasizing posterior uveal melanoma, but also in developing appropriate strategies for follow-up and treatment.

Atypical, severe toxoplasmic retinochoroiditis in elderly patients

BACKGROUND

The diagnosis of toxoplasmic retinochoroiditis is based primarily on characteristic ocular findings, with supportive serologic evidence. Clinical recognition of atypical presentations is critical for timely antiparasitic drug therapy.

METHODS

Case histories were reviewed for seven presumed immunocompetent elderly patients with atypically severe (multifocal or diffuse or both) toxoplasmic retinochoroiditis. Three cases initially were misdiagnosed as acute retinal necrosis syndrome. The correct diagnosis was confirmed in each case by response to antiparasitic drug therapy, polymerase chain reaction studies of intraocular specimens, or histopathologic analysis.

RESULTS

The patients ranged in age from 69 to 82 years (median, 74 years). Only three patients had intercurrent medical conditions that may be associated with subtle immune dysfunction (diabetes mellitus and hepatitis C). The extensive necrotizing retinochoroiditis in each patient was nonhemorrhagic and not associated with occlusive retinal arteritis. Despite prompt response to antiparasitic drug therapy, prolonged treatment usually was required, and four patients had retinitis reactivation after discontinuing treatment. Significant visual loss accompanied the infection in most eyes.

CONCLUSION

Toxoplasmosis should be considered as a cause of multifocal or diffuse necrotizing retinitis or both in elderly patients. Older patients may be more susceptible to severe ocular Toxoplasma infections because of age-related decline in cell-mediated immunity and chronic underlying diseases.

Serum protein electrophoresis: potential test for use in geriatric companion animal health programmes

The electrophoretic patterns of 117 serum samples from 37 clinically healthy old dogs (age: 10.0 +/- 2.5 years, mean +/- SD) 47 old dogs (age: 9.7 +/- 2.0 years) with different diseases, 18 clinically healthy young dogs (age: 2.9 +/- 1.6 years) and 15 young dogs (age: 2.0 +/- 1.0 years) with different diseases were evaluated using agarose as a supporting matrix. Three major electrophoretic patterns were identified after densitometric scanning. The first pattern was a predominant pattern for the young healthy dogs (found in 67% of dogs in that group) and was considered normal for healthy dogs. The second pattern had relatively higher proportions of beta and gamma globulins (polyclonal immunoglobulinaemia) and was a predominant pattern among the old healthy dogs (found in 51% of dogs in that group). The findings regarding the second pattern appear to suggest that they had been exposed to antigens during their lives and that they had a well developed and responsive humoral immune response. The third pattern was characterized by high levels of alpha globulins, it was the most common pattern in the old diseased dogs (found in 70% of the dogs in that group). The third pattern was considered to indicate an inflammatory response among old dogs when compared to young dogs (P < 0.01). These patterns appear to suggest that because of aging and/or accumulated injury geriatric dogs will have high levels of polyclonal gamma-globulinaemia or acute phase reactants. The observed patterns, especially the one showing high levels of alpha-globulins, could be a valuable parameter in the search for individuals requiring special attention and thus for the establishment of health programmes for geriatric dogs. With further effort, serum protein electrophoresis might prove to be a useful test for the evaluation of geriatric companion animals for diagnostic, prognostic and therapeutic reasons.

Patient death after renal transplantation--an analysis of its role in graft outcome

Whether patient deaths among renal transplant recipients should be counted as transplant failures when they occur while the transplant is still functioning is a controversial issue. Analyses of more than 45,000 first cadaver transplants reported to the UNOS Scientific Renal Transplant Registry between October 1987 and March 1995 showed that deaths among transplant recipients were strongly associated with the patient's age and presence of insulin-dependent diabetes. Other factors associated with poor early graft function were also associated with a significantly increased risk of death. Deaths within the first 5 years increased from 9% of recipients aged 2-15 to 30% of those over age 45 (P < 0.001). Deaths with a functioning graft occurred in 2% of the youngest patients and 13% in the older age group (P < 0.001). Among diabetics, 32% died within 5 years (12% with a functioning graft) compared with 10% (6% with graft function) of patients with glomerulonephritis (P < 0.001). When the transplanted kidney failed to function immediately or the patient required dialysis during the first week after transplant, 30% of patients died within 5 years compared with 20% when the graft functioned (P < 0.001). There was no difference in the percentage of deaths with a functioning graft. We conclude that deaths among renal transplant recipients follow an expected pattern in which the likelihood of death increases with age and diabetes.

Tumor necrosis factor-alpha (TNF-alpha) induces a reversible, time- and dose-dependent adhesion of progenitor T cells to endothelial cells

Recent in vivo studies suggest that tumor necrosis factor-alpha (TNF-alpha) is involved in the development of the thymus. We postulated that this inflammatory mediator could regulate the influx of progenitor T cells into the thymus. Using an in vitro static adhesion system, we found that TNF-alpha increases the adhesion of a murine progenitor T cell line (FTF1) to a bovine aortic endothelial cell line (1F8), human umbilical vein endothelial (HUVE) cells, and a murine arterial endothelial (MAE) cell line. TNF-alpha treatment of the 1F8 cells resulted in a time- and dose-dependent increase in the adherence of FTF1 cells. Adherence increased during the first 6 hr of treatment with TNF-alpha concentrations ranging from 10(-11) to 10(-9) M. Maximal adherence (6 hr treatment with 10(-10) M of TNF-alpha) was approximately 4.5-fold larger than that of untreated monolayers. A slow decrease in adherence, down to approximately 2-fold at 48 hr, was observed beyond 12 hr of TNF-alpha treatment; in contrast, removal of TNF-alpha after 6 hr of continued stimulation caused the adherence to return to pre-stimulation levels within 24-30 hr. Adhesion of FTF1 cells to TNF-alpha treated 1F8 cells was almost completely blocked by a monoclonal antibody against murine CD49d (very late antigen-4) expressed on FTF1 cells. TNF-alpha-induced adhesion of FTF1 cells to MAE cells was also blocked by monoclonal antibodies against murine CD49d and CD106 (vascular cell adhesion molecule-1). These results support the notion that local secretion of TNF-alpha could modulate the dynamics of adhesion of progenitor T cells to the thymic endothelium.

Human lymphocytes incubated in vitro share multiple characteristics with geriatric-derived lymphocytes: a potential in vitro model for aging?

Aging involves a complicated set of parallel reactions that result in multiple cellular and organismic changes and may eventuate in chronic illness. In the immune system, several alterations that correlate with age have been established. In the present study, we report the results of incubating lymphocytes in vitro in whole blood and, employing measures known to be age-dependent, compare these cells 'aged' in vitro with cells from geriatric patients aged in vivo. Cells from blood aged in vivo and incubated in vitro share a number of common characteristics that include decreased growth capacity, shifted growth patterns, increased suppression by adherent cells, decrease in CD5 surface antigen, similar responses to addition of exogenous IL-1, IL-2, PGE2, or indomethacin, and similar production of PGE2. Differences found between in vivo aging and in vitro incubation are IL-2 plasma levels and IL-2 production by activated cells monitored in conditioned minimal medium. Based on these observations, this in vitro system provides a simple method to generate cells that exhibit a very significant subset, but not all, of the characteristics associated with in vivo aging in lymphocytes.

Renal transplantation for patients 60 years of older. A single-institution experience

OBJECTIVE

The authors reviewed renal transplant outcomes in recipients 60 years of age or older.

BACKGROUND

Before cyclosporine, patients older than 45 years of age were considered to be at high risk for transplantation. With cyclosporine, the age limits for transplantation have expanded.

METHODS

The authors compared patient and graft survival, hospital stay, the incidence of rejection and rehospitalization, and the cause of graft loss for primary kidney recipients 60 years of age or older versus those 18 to 59 years of age. For those patients > or = 60 years transplanted since 1985, the authors analyzed pretransplant extrarenal disease and its impact on post-transplant outcome. In addition, all surviving recipients > or = 60 years completed a medical outcome survey (SF-36).

RESULTS

Patient and graft survival for those > or = 60 years of age versus those 18 to 59 years of age were similar 3 years after transplant. Subsequently, mortality increased for the older recipients. Death-censored graft survival was identical in the two groups. There were no differences in the cause of graft loss. Those 60 years of age or older had a longer initial hospitalization, but had fewer rejection episodes and fewer rehospitalizations. Quality of life for recipients 60 years of age or older was similar to the age-matched U.S. population.

CONCLUSION

Renal transplantation is successful for recipients 60 years of age or older. Most of them had extrarenal disease at the time of transplantation; however, extrarenal disease was not an important predictor of outcome and should not be used as an exclusion criterion. Post-transplant quality of life is excellent.

Immunological alterations with aging—laying a stress on recent progress in Japan

Age-related decline of immune functions mainly occurs in the T-cell-dependent immune system and this is precede by physiological thymic involution starting after puberty. Age-related alterations of T cells are seen in their number, subsets and qualities. In relation to the qualitative change of aging T cells, disturbance of intracellular signal transduction is responsible for the impairment of proliferation and cytokine production upon antigenic stimulation. Thymus, but not bone marrow, is responsible for aging of the T-cell-dependent immune system. The thymic capacity to induce T cells starts to decline early in life. Older thymus induces different subsets of T cells which are functionally less active T cells than those of young thymus. In association with a decline in immune functions to exogenous antigens, autoimmune phenomena increase with advance of age, which are observed as production of autoantibodies and auto-reactive T cells. The possible site for controlling thymic function is discussed.

Aged lymphocyte proliferation following incorporation and retention of dietary omega-3 fatty acids

T cell activation involves events at the plasma membrane; therefore, molecules such as long chain omega-3 fatty acids that alter the structure of the plasma membrane may affect the activation of aged T cells. In this project we investigated whether the incorporation of omega-3 fatty acids (from fish oil), in the presence of vitamin E, improves age-diminished T cell proliferation. Young and old mice were fed diets rich in either fish (menhaden) oil or saturated fat for various lengths of time. Splenocytes were harvested from these mice and stimulated in culture with either mitogen or the antigen keyhole limpet hemocyanin (for a secondary response); proliferation was estimated by [3H]thymidine incorporation. We found no discernible effect of dietary omega-3 fatty acids (with vitamin E supplementation) on lymphocyte proliferation stimulated by the mitogens concanavalin A or phytohemagglutinin. We did, however, find that the saturated fat diet and the menhaden oil diet in young mice lowered protein kinase C activities in the particulate fractions of spleen cells when compared to chow-fed mice. Middle-aged and old mice were less affected by the experimental diets than young mice, but they demonstrated decreased protein kinase C activity as well. These alterations did not affect the ability of splenocytes to respond to mitogenic stimulation. Fatty acid analysis revealed that lymphocytes from mice fed saturated fat for 8.5 months retained significant amounts of the omega-3 fatty acid docosahexaenoic acid, despite the lack of dietary omega-3 fatty acids. However, when aged (but not young) lymphocytes were clonally expanded by antigen in vivo in the presence of dietary omega-3 fatty acids, they produced a greater secondary proliferative response than old lymphocytes expanded during a saturated fat diet. Although our results suggest that omega-3 fatty acids may enhance aged lymphocyte proliferation, the tenacious retention of these fatty acids makes comparison with omega-3-depleted lymphocytes difficult.

Understanding the mechanism of the age-change of thymic function to promote T cell differentiation

Immunological functions peak at around puberty and gradually decline thereafter with advancing age. The immunological decline mainly occurs in the T cell-dependent immune system and is generally associated with an increase in not only susceptibility to infections but also incidence of autoimmune phenomena. The age-related changes in T-cell dependent immune functions can be mainly ascribed to the physiological thymic involution which starts in the early phase of life. The age-related thymic involution can be ascribed to either extrinsic or intrinsic factors. Bone marrow stem cells can be one of the extrinsic factors for the thymic involution, but their role is estimated to be marginal as compared with alteration of the thymic microenvironment. With advancing age, the thymic capacity to promote T-cell differentiation declines together with a change in the composition of T-cell subsets produced. Such an alteration of the thymic environment is responsible for the age-related change in peripheral T cells in number and in composition. Age change is observed in several intrinsic factors in the thymic environment which influence proliferation of thymocytes. These thymic intrinsic factors can either promote or inhibit proliferation of thymocytes, and promoting factors generally decrease with age with a concomitant increase in inhibitory factors. Various endocrine hormones are important extrinsic factors influencing the thymic function. In fact, physiological thymic involution can be intervened by manipulation of the endocrine system, sometimes resulting in rejuvenation of immune functions to a certain extent.(ABSTRACT TRUNCATED AT 250 WORDS)

Humoral immunity in aging

The interactions between B and T lymphocytes, leading to the development of humoral responses, are reviewed with references to the changes occurring in aged people. Aging is perceived as a process of impairment of immune functions; it is known that T cells from aged subjects have a reduced ability to produce IL-2. However, other functions seem to be upregulated in elderly subjects; indeed, IL-1, IL-3, IL-4, IL-6 and TNF alpha production are increased both in aged mice and humans. These cytokines are known to control B cell differentiation, through isotype switch and Ig production. A significant increase in IgG subclasses and IgA is observed in sera of aged subjects. This contrasts with the significant decrease in circulating B lymphocytes. The impairment of primary responses to immunization, and other aspects of humoral immunity, including mucosal responses, autoantibody production and correlations with phenotypic markers of T and B cell subsets, are discussed.

Renal transplantation in older people

Renal transplantation in people 60 years old or more is controversial due to the morbidity associated with immunosuppression and the scarcity of renal allografts. We have reviewed the outcome of 1222 consecutive renal transplants done at a single institution with a uniform immunosuppressive protocol over 10 years. 5-year graft survival was the same in the under sixties as in the sixties and over. Patient survival was worse in the older group (p = 0.0001), but there were significantly fewer immunological graft losses: 11% vs 31% (p = 0.0009; relative risk [RR] = 0.36 [95% confidence interval 0.19-0.66]). A majority of the deaths in both groups were secondary to cardiovascular disease, not due to complications of immunosuppression. We conclude that renal transplantation in people 60 and over has results equivalent to a younger population. Age 60 and over should not be a major factor in considering if a patient is eligible for renal transplantation.

Effects of a protein-free diet or food restriction on the immune system of Wistar and Buffalo rats at different ages

The effects of a protein-free diet or food restriction on the immune system were examined in two rat strains, Wistar and Buffalo, in different age-groups. Unlike Wistar rats, Buffalo rats have an unusually hyperplastic thymus and a large number of peripheral T cells. The protein-free diet (PFD) in rats resulted in marked thymic involution together with a reduction of splenic T cells, both in number and in antibody response to sheep red blood cells. The depressive effect of the PFD on the immune system was more serious in young immature rats than in older rats, but less serious in Buffalo rats having enhanced T cell functions regardless of age. Thymic involution was also accelerated in both strains of rats by feeding them a restricted amount of the control diet containing well-balanced nutrients (food restriction, FR). In the FR experiment, no significant change was observed in immune functions of Wistar rats. A slight reduction was observed in the immune functions of Buffalo rats with FR, but absolute levels were distinctly higher in Buffalo rats than in Wistar rats even after FR. These results suggested (1) that the thymic function is sensitive to protein deficiency; (2) that a well-balanced dietary condition is necessary for immunological maturation in the early stage of life and preservation of immune functions at older age; (3) that animals having higher immune functions are more resistant to malnutrition than ordinary ones.