Immunosenescence. Clinical and pharmacologic considerations

Physical inactivity and smoking increase risk for serious infections in older women

OBJECTIVE

This study examined health and behavioral risk factors for infections that required hospitalization in postmenopausal women who were enrollees of a large health maintenance organization (HMO).

METHODS

Participants were 1,365 generally healthy women aged 55 to 80 years who were followed for up to 6 years. Infection diagnoses listed first in the automated hospital discharge records were used to identify hospitalizations for which infections were the primary cause of admission. Potential risk factors for these serious infections were identified from baseline questionnaire information and automated HMO records from before baseline and during follow-up. Risks for infections associated with hospital admission were examined using multivariate logistic regression methods.

RESULTS

Seventy-three women had a total of 90 hospital admissions in which infection was the primary discharge diagnosis. Behaviors that were independent predictors of infection were physical inactivity (adj. odds ratio = 4.08; 95% CI, 1.73-9.63) and smoking (adj. odds ratio = 2.64; 95% CI, 1.11-6.26). Incident cancer and lung disease were also associated with increased risk of infection. These associations were independent of age, body mass index, functional status, and other measures of health.

CONCLUSIONS

Modifiable risk factors such as physical inactivity and smoking may place older women at risk for serious infections although the causal link is yet to be explained. Further research in this area may lead to new strategies aimed at reducing the serious burden of infections in the older population.

Aging, immunity, and cancer

BACKGROUND

The prime function of the immune system is to protect the entire organism from a variety of insults and illnesses, including the development of cancer. The question of how age-related declines in immune function contribute to an increasing incidence of malignancies continues to be a focus of discussion and speculation.

METHODS

The recent literature from the National Library of Medicine database (1990 through the present) was searched for articles using the medical subject headings (MeSH terms) of aging, immunity, cancer, senescence, and apoptosis. Bibliographies of articles retrieved were also scanned.

RESULTS

Data from in vitro and in vivo animal and human studies demonstrate clear age-related alterations in both the cellular and humoral components of the immune system, but there is little evidence supporting direct causal links between immune senescence and most malignancies.

CONCLUSIONS

Senescent decline in immune surveillance leads to the accumulation of cellular and DNA mutations that could be a significant factor in the development of malignancy and programmed cell death or apoptosis observed in the elderly.

Age-associated changes in interferon-gamma and interleukin-4 secretion by purified human CD4+ and CD8+ T cells

Aging is associated with a decline in immune function. Interferon-gamma (IFN-gamma) and interleukin-4 (IL-4), two important immune deviation-related cytokines, are mainly produced by type 1 and type 2 T cells, respectively. To investigate the age-associated changes in the secretion of these two cytokines, 20 elderly and 20 young subjects fulfilling the SENIEUR protocol were enrolled. The ratios of CD4+ to CD8+ T cells were not different between the two age groups. The CD4+ and CD8+ T cells were purified by a magnetic cell sorting system, and then activated by concurrent anti-CD3 and anti-CD28 stimulation. The released cytokines were determined by ELISA. Both the CD4+ and the CD8+ T cells of the elderly individuals secreted a significantly larger amount of IFN-gamma after activation. Profound IL-4 production by CD8+ T cells was observed in the older subjects compared with that of the young subjects. These data suggested that age-associated decrease in immunity may be related to an imbalance in the secretion of immune deviation cytokines. The number of IL-4-secreting CD8+ T cells (T cytotoxic 2) rose significantly in the older individuals. Our design also provided a useful way to differentiate the T cell subsets secreting the same cytokine, such as IFN-gamma-producing T helper 1 and T cytotoxic 1 cells.

Modulating effects of the synthetic thymic dipeptide pidotimod on the immune system in the aging rat

We have investigated the in vivo and in vitro effect of pidotimod, a synthetic thymic-derived drug, on the immune response in young (2 month-old), and aging (24 month-old) Sprague-Dawley rats. We studied the effect of different doses of pidotimod on the responsiveness of both cultured peripheral blood lymphocytes and splenocytes to mitogenic stimuli, as well as on interleukin-2 production by peripheral blood lymphocytes after stimulation with interleukin-1 and phytohemagglutinin. Treatment with pidotimod in vivo as well as in vitro resulted in an increase of tritiated thymidine incorporation in both mitogen-stimulated lymphocytes and splenocytes from 24 month-old rats. Production of IL-2 from lymphocytes of 24 month-old rats was significantly increased in groups of animals treated with pidotimod. On the other hand, treatment with pidotimod did not influence the responsiveness of 2 month-old rat lymphocytes to mitogens, nor affected IL-2 production. Our results suggest a possible specific modulatory activity of pidotimod on the aging immune system.

Increased oxygen tensions influence subset composition of the cellular immune system in aged mice

In acute and chronic experiments, each of eight groups of aged mice were assigned separately to different pressures of oxygen to which it was to be exposed. Lymphocytes from spleen, thymus, and peripheral blood were analyzed following oxygen exposure. Subset populations changed depending on the oxygen tension. Variable changes were observed in total numbers of lymphocytes, lymphocyte subsets, B cells, and macrophages depending on the organ studied and the oxygen pressure to which the mice were exposed. There were differences between acute and chronic exposure suggestive of adaptation to environmental stressors. The suggestion is made that the immune system has a reserve capacity that can be influenced by oxygen and, thereby, theoretically capable of being pharmacologically manipulated to assist patients with altered immune systems to promote defense mechanisms or, under certain circumstances, reduce autoimmunity. It is hypothesized that an underlying hypoxia may be involved in the age-associated decline in the immune system.

Investigations of the lymphokine system in elderly individuals

Elderly people are at risk from an increased incidence of infections. Therefore we have studied the correlation between the production of several immunological parameters such as interferon-gamma (IFN-gamma), interferon-alpha-2 (IFN-alpha-2), interleukin-2 (IL-2), soluble interleukin-2 receptors (sIL-2R) and interleukin-6 (IL-6) in young controls of 25-34 years old and old individuals with a minimum age of 65 years. All persons were selected according to the basic concept of the 'Senieur protocol'. Heparinized blood was taken and cultured in the whole-blood assay. The determination of all cytokines in the supernatants of stimulated cultures was done by the ELISA technique. We found significantly decreased levels of sIL-2R and IFN-alpha-2 after stimulation, whereas the values of IFN-gamma and IL-2 showed no significant difference between elderly and young persons. The values of IL-6 showed a distinct trend towards an increased synthesis for the elderly. We also studied the lymphocyte subpopulations T4 and T8 by flow cytometry. Elderly individuals showed a significantly increased T4/T8 ratio, caused by a slightly but not significantly decreased level of T8 cells. These results show that the elderly have decreased values of some immunological parameters such as IFN-alpha-2 and sIL-2R, which might explain an increased susceptibility of elderly individuals to bacterial and viral infections.

Antibody affinity disturbance in the immunoglobulin immune response to mucosal antigenic stimulation in lung cancer. The Betalactoglobulin Model

BACKGROUND

This study is a continuation of a recent study, in which a defect in the immunoglobulin G (IgG) response to some natural antigens (bovine betalactoglobulin [BLG] from cow's milk and antigen p1 from the house dust mite Dermatophagoïdes pteronyssinus), usually presented at the mucosal level, was documented in lung cancer patients. The present study further characterizes this difference in terms of antibody relative functional affinity in the BLG model.

METHODS

Relative functional affinity was evaluated by solid-phase enzyme-linked immunosorbent assay in terms of the relationship between specific IgG retention, assessed with peroxidase-labeled protein A, and serial dilutions of IgG fractions isolated from 24 sera from lung cancer patients and 24 sera from healthy control subjects matched for their anti-BLG IgG antibody titers. The procedure was performed in the presence and absence of low concentrations of diethylamine, which was expected to prevent low-affinity antigen-antibody binding without affecting the binding of high-affinity antibodies. Anti-BLG IgG antibody affinity also was evaluated in 25 patients with early-stage lung cancer, before and after (5 +/- 1 week) complete surgical excision of the tumor.

RESULTS

Results, expressed as the slope of the binding curves and their leftward shift induced by diethylamine, showed different antibody populations between the two groups. Control sera showed a heterogeneous population of anti-BLG IgG antibodies, including antibodies of higher (steeper slope) and lower (more gradual slope) functional affinity. Cancer sera exhibited a less heterogeneous population of anti-BLG IgG antibodies, mostly with lower functional affinity. No change was observed in anti-BLG IgG antibody affinity in the 25 lung cancer patients tested 5 +/- 1 week after complete surgical excision of the tumor.

CONCLUSIONS

These results document a persistent qualitative immunologic disturbance in patients with lung cancer, regardless of the type and extent of tumor. The potential relationship between this observation and the development of lung cancer, however, is presently unknown.

Immune parameters in a population of institutionalized elderly subjects: influence of depressive disorders and endocrinological correlations

Twenty-six institutionalized elderly subjects, selected as healthy according to the SENIEUR protocol, were compared to adult controls to establish correlations between affective disorders and immune abnormalities and to investigate underlying neuroendocrine mechanisms. After an extensive psychodiagnostic examination, 35% of the aged subjects were classified as depressed. Cutaneous delayed hypersensitivity tests showed reduced responses in the aged, but no correlation was found with the psychological status. Examination of the peripheral blood lymphocyte subsets revealed no imbalance in the percentages of CD3+, CD4+, CD8+ cells in the aged. A slight reduction in the CD4+/CD8+ cell ratio could however be detected in the non-depressed aged, as compared to adult controls. The CD4+/CD45R+ cell subset was reduced in non-depressed aged. The percentage of B lymphocytes was reduced in the aged, mostly in the non-depressed subjects. No changes were detected in the percent of OKDR+ cells. The percentage of CD16+ cells was found unchanged, while that of Leu7+ cells was significantly higher in the aged than in the adults and in the non-depressed than in the depressed aged. Leu7+ cell levels were negatively correlated with the depression score. On double labelling, the percent of CD16+/Leu7+ cells appears increased in the subgroup of depressed aged and positively correlated with age. Plasmatic and urinary cortisol levels were both positively correlated with depression score. Urinary cortisol level was higher in the depressed aged. These parameters, as well as plasmatic ACTH, beta-endorphin and urinary catecholamines, were not correlated with immune responses. Based on these findings, we recommend that the neuroendocrinological conditions should be taken into account when healthy subjects are examined in studies of immune senescence.

Lymphocyte immunophenotyping in an elderly population: age, sex and medication effects--a flow cytometry study

Flow cytometry studies of 179 individuals aged 55-95 years reveal correlations of various hematological and immune cell measures (quantification of leukocytes, leukocyte subtypes, platelets, and erythrocytes) with age, sex, common medications (aspirin, ulcer therapy, estrogen replacement therapy), and health history variables (minor arthritis, allergy, smoking, stress and exercise). Possible reasons for some of these findings are discussed.

Anergy testing in nursing home residents

Delayed cutaneous hypersensitivity (DCH) testing is commonly used to determine exposure to Mycobacterium tuberculosis and in the evaluation of cellular-mediated immunity. Many reports indicate that anergy to ubiquitous antigens is common in the elderly. Recent studies suggest that anergy in the aged is not common when five or more antigens are used. Because it is often difficult to purchase singularly or apply a larger number of quality DCH antigens, we investigated the usefulness of the Multitest CMI in 29 nursing home residents with chronic diseases. This device simultaneously applies seven skin test antigens and a negative control. Ten young healthy subjects served as controls. DCH reactions were scored based on the sum of induration and total number of positive responses. Although elderly subjects had significantly lower scores than the young subjects, only 7% of elderly subjects were anergic. Our data indicate that the Multitest CMI is a highly effective device to test for DCH in geriatric subjects with chronic diseases. Although skin test responses in these subjects were blunted, in most residents cellular-mediated immunity remained intact.

Pharmacologic immunoenhancement in the elderly: in vitro effects of isoprinosine

The loss of immune competence that occurs with aging may be responsible for increased morbidity and mortality in elderly individuals. Pharmacologic modulation of the immune response might reverse the immunologic aberrations associated with aging. We, therefore, investigated the effects of isoprinosine, an immunoenhancing drug, on selected in vitro immune responses in elderly subjects. Subjects studied were 65 years of age or older, and all had chronic diseases. We chose this population since they were at greatest risk for morbid events. Isoprinosine significantly enhanced mitogen-stimulated mononuclear cell proliferation, did not affect unstimulated cell growth, and needed to be present for the entire culture period for maximum effect. Isoprinosine is a potent in vitro immunoenhancing agent in aged humans.

The influence of host factors on the outcome of a viral infection

The clinician confronted with a patient that has an infectious disease, particularly one caused by a virus, faces a series of difficult problems: diagnostic confirmation of the infection, instituting appropriate therapy, duration of treatment, preventing secondary complications, and preventing transmission of the virus to susceptible animals. Yet, it is the complex relationship between the patient, as host to a pathogenic virus, the virus, and the environment that ultimately influences the clinical course of an infection. The ability to accurately prognose the outcome of any infection is, therefore, predicated on the clinician's awareness of biological and environmental variables that apply to the individual patient.