Age-related impaired proliferation of peripheral blood mononuclear cells is associated with an increase in both IL-10 and IL-12.

Reflective of age-associated decline in immune function among elderly individuals is a decrease in in vitro T cell proliferative ability. Impaired T cell proliferation in the elderly may result from disruption of the well-balanced network of regulatory cytokines produced during an immune response. The purpose of this study was to identify age-related changes in the production of interleukin (IL)-10 and IL-12, and to determine whether in vitro T cell proliferation can be enhanced in the elderly by modulation of these two key cytokines. The superantigen Staphyloccocus entertoxin B (SEB) was used to stimulate proliferation and IL-10 and IL-12 production in peripheral blood mononuclear cells (PBMC) in vitro. Proliferation was determined by standard tritiated thymidine uptake. Cytokine levels in culture supernatants were measured by ELISA. We observed impaired SEB-induced proliferation of PBMC in the elderly that is comparable to that seen with the polyclonal mitogen Con A. This age-related decline in proliferation was associated with increased production of both IL-10 and IL-12. Modulation of PBMC proliferative response with either recombinant IL-12 or IL-10-neutralizing antibodies can boost proliferation of elderly PBMC to the levels seen in unmodulated young controls.

Antigen presenting cell function is enhanced in healthy elderly.

Aging is associated with a progressive decline in T cell-mediated immune responses. Little is known about the effect of aging on antigen presenting cells (APC). We have recently reported an age-related decline in proliferative response of peripheral blood mononuclear cells from elderly volunteers to Staphylococcus enterotoxin B (SEB). Since SEB-induced stimulation of T cells is not restricted by major histocompatibility complex, experiments were conducted in which T cells and APC from young and healthy elderly subjects were combined. We initially demonstrated the decreased SEB-induced proliferative capacity of elderly T cell elderly APC co-cultures when compared with young T cell young APC co-cultures. Combination of purified T cells from elderly donors with APC from young donors maintained a reduced T cell proliferative response. Age-related decline in T cell function was also established by the reduced proliferative capacity of elderly T cells co-cultured with a reference monocyte cell line. Surprisingly, co-culture of APC from healthy elderly donors with purified T cells from young donors enhanced T cell proliferation. APC from elderly donors also marginally enhanced the proliferative response of an SEB-specific T cell line.

T cells are the cellular target of the proliferation-augmenting effect of chronic low-dose ionizing radiation in mice.

The proliferative response to mitogenic stimulation by splenocytes can be augmented by exposing mice to whole-body, chronic, intermittent low doses of ionizing radiation, referred to here as low-dose irradiation. The purpose of this study was to identify the cell(s) in the spleen which is responsive to the proliferation-augmenting effect of low-dose irradiation, i.e., the cellular target. C57BL/6 mice were subjected to low-dose irradiation (0.04 Gy/exposure/day, 5 consecutive days/week, 2 weeks) or to sham irradiation. Three days after the last exposure, spleens were removed, separated into cell fractions which were nonadherent and adherent to plastic surfaces and reconstituted in various combinations, and their proliferative responses to various mitogens were determined. Highly purified T cells were also used in place of the nonadherent cell fraction in the reconstitution studies. The target cells were shown to be T cells. The target T cells of low-dose-irradiated mice possessed elevated constitutive levels of HSP-70 mRNA and HSP-72, and they responded to T-cell receptor-specific anti-CD3 stimulation by producing more HSP-70 mRNA and HSP-72 and by proliferating more extensively than T cells of sham-irradiated mice.

Combined chronic low dose radiation-caloric restriction: a model for regression of spontaneous mammary tumor.

PURPOSE: This study was carried out to determine whether chronic low dose radiation can act alone or in synergy with restricted diet in down-regulating spontaneously occurring mammary tumor in tumor-susceptible female C3H/He mice and whether immune cells are involved. METHODS AND MATERIALS: At 7 months of age, one-half of the experimental mice were maintained on an ad lib diet, and the other half was adapted over a period of 1 month to a diet of 70% of the daily amount of food consumed by the ad lib-fed mice. The food of the restricted diet was enriched such that the vitamin and mineral intake was the same for both groups. Half of the mice in each group was then subjected to chronic low dose radiation (0.04 Gy per exposure from a 60Co source, 3 x-per-week for 4 weeks) and the other half was sham irradiated. The 70% calorically restricted diet was maintained throughout the study. RESULTS: Chronic low dose radiation alone was ineffective in down-regulating spontaneous mammary tumor, unlike caloric restriction. However, chronic low dose radiation when combined with caloric restriction promoted regression of mammary tumors, which were infiltrated with massive numbers of CD8+ T cells. These phenomena were not seen in mice subjected to caloric restriction alone. CONCLUSION: Combined chronic low dose radiation-caloric restriction appears to be a useful model for promoting spontaneous mammary tumor regression.

Double-negative (L3T4-, Lyt2-) thymocytes of autoimmune lpr/lpr mice are resistant to down-regulation of DNA synthesis by a thymic stromal cell product.

The murine autosomal recessive gene, lpr, induces a progressive lymphadenopathy and lupus-like autoimmune syndrome characterized by the accumulation of immature, dull Thy 1.2+, TCR+, L3T4-/Lyt 2- (double-negative, DN) T cells in peripheral lymphoid organs. Previous studies demonstrated that the thymic microenvironment is required for the generation of the abnormal, peripheral DN T cells, while a more recent report linked the lpr gene defect with a failure of thymocytes to express a functional form of the Fas antigen, which mediates apoptosis. Thus, the lpr gene defect apparently prevents lpr thymocytes from responding to the ordered sequence of differentiation and proliferation signals involved in normal thymocyte maturation and selection. We compared the responses of thymocytes from C57BL/6 +/+ (normal) and congenic C57BL/6 lpr/lpr (lpr) mice to a thymic stromal cell product which down-regulates DNA synthesis in vitro. The results indicate that (a) thymic stromal cells from lpr mice produce a factor that can down-regulate DNA synthesis as efficiently as that from normal mice, even at an age when massive lymphadenopathy is present, (b) mitogen-stimulated thymocytes of normal, but not lpr, mice are sensitive to the inhibitory factor, (c) normal DN thymocytes are the cellular target of the inhibitory factor, which acts at some postmembrane receptor-ligand binding event during mitogen-stimulated proliferation, and (d) IL-4-dependent DN thymocyte proliferation seems to be the main target of the inhibitory factor.

Mice chronically exposed to low dose ionizing radiation possess splenocytes with elevated levels of HSP70 mRNA, HSC70 and HSP72 and with an increased capacity to proliferate.

The purpose of this study was to determine whether the enhanced proliferative activity of splenocytes induced by exposing mice to whole body, chronic, intermittent low doses of ionizing radiation is associated with an increase in the expression of stress protein genes. Mice were exposed to a gamma-irradiation protocol of 0, 0.04 or 0.10 Gy/day for 5 consequent days/week, for 4 weeks. Splenocytes were then assessed for their levels of heat shock protein (HSP) 70 mRNA, glyceraldehyde 3-phosphate dehydrogenase (GAPD) mRNA, HSC70 (a constitutively-expressed isoform of HSP70) and HSP72 (an inducible isoform of HSP70), before and 1 day after mitogenic stimulation. Splenocytes from mice exposed to 0.04 Gy/exposure contained elevated constitutive levels of HSP70 mRNA, HSC70 and HSP72. These splenocytes responded to T, but not B, cell mitogens by further increasing their levels of HSP70 mRNA, HSC70 and HSP72 and by mounting a heightened proliferative response. However, an exposure of 0.10 Gy was ineffective. Thus, the constitutive levels of HSP70 mRNA, HSC70 and HSP72 and the mitogen-stimulated levels of HSC70 and HSP72 of splenocytes from mice exposed to 0.10 Gy/exposure were comparable with those of sham-irradiated mice. Moreover, their proliferative activity in response to mitogenic stimulation was also comparable with that of splenocytes from sham-irradiated mice.

DNA strand breaks and DNA repair response in lymphocytes after chronic in vivo exposure to very low doses of ionizing radiation in mice.

In contrast to the well-documented negative effects of high-dose oxidant exposure, accumulating evidence supports a positive, perhaps essential physiologic role for very low-level oxidant stress. For example, low-level oxidant exposure, within or below the physiologic range, has been reported to stimulate membrane signal transduction, proliferation, antioxidant defense and DNA repair. In the present study, we have examined whether whole-body exposure to low-dose radiation (LDR) results in an alteration in constitutive (steady state) levels of DNA-strand breaks and whether an adaptive increase in DNA-repair response is induced. C57B1/6J mice were exposed to 0.04 Gy (4 cGy) of gamma-radiation as a model of low level oxidant stress. End points measured after chronic in vivo LDR included: (1) constitutive expression of DNA-strand breaks in quiescent spleen cells; (2) sensitivity to DNA damage after high-dose radiation exposure in vitro; (3) repair of constitutive and radiation-induced DNA strand breaks after mitogen stimulation: (4) activity of the DNA-repair associated enzyme, poly(ADP-ribose)transferase (ADPRT) and its substrate, NAD. The results indicated that the constitutive expression of DNA-strand breaks is significantly decreased after chronic LDR; however, DNA-repair capacity after high-dose radiation exposure is not increased above that observed in sham-irradiated mice. Associated with the reduction in constitutive DNA-strand break accumulation was a decrease in resting levels of the DNA-repair-associated enzyme poly(ADP-ribose) transferase (ADPRT). These results are consistent with the interpretation that cumulative DNA damage and associated DNA-repair activity in unstimulated cells are both reduced after chronic LDR exposure.

Immunological changes in young and old adults during brief laboratory stress.

Few data are available on the response of the human immune system to acute psychological stressors under controlled laboratory conditions. Young female subjects (21-41 years) showed increases in natural killer (NK) cell activity, and in the numbers of circulating CD8 suppressor/cytotoxic T cells, and natural killer lymphocytes following a brief (12 minute) stressful mental arithmetic examination. Older female subjects (65-85 years) failed to show the stress-related increase in NK activity. The psychological stress did lead to increases in the numbers of circulating CD8 suppressor/cytotoxic T cells and NK lymphocytes in old subjects to a similar degree as that seen in the young group. No changes in the numbers of helper/inducer T cells (CD4), total T cells (CD3), or B cells (CD20) were found following the stressor for either group. Cardiovascular, catecholamine, and subjective stress responses were similar for the two age groups. These results demonstrate that brief psychological stress is associated with some rapid immune cell changes, including release of CD8 suppressor/cytotoxic T cells and NK cells into circulation, and in young subjects, increases in NK activity. The absence of an NK activity increase in the older subjects indicates that NK cell mobilization and cell lysis induced by NK cells may be differentially affected by stress. The results also suggest the possibility of an age-related deficit in the up-regulation of NK activity under some environmental demands.

Cellular immunosenescence: an overview.

Recent studies on space flights suggest that certain T cell immunologic activities are vulnerable to microgravitation. It would be desirable to know the extent to which these changes can be prevented or reversed. Since the changes observed are analogous to the effects of aging on immunity, a brief overview is presented of our current knowledge of age-related changes in immune cells and of the various interventional methods which have been used successfully in preventing the decline with age and in elevating the levels of immune functions of old individuals.

The aging process.

The intricate cause of the aging process in humans and animals, at present a matter of intense speculation, has given rise to many theories. Despite its uncertain cause, aging constitutes the most significant and universal problem confronting physicians today. Age-related physiologic deterioration and age-associated diseases are of immense concern to physicians because of the "old-age boom" anticipated in the first part of the twenty-first century. Biomedical research achievements in the twentieth century have permitted more persons to approach the fixed upper limit of the human lifespan. We discuss the functional decline of the aging heart and the underlying mechanisms of that decline; quantitative and qualitative changes in the immune system; and normal aging of the human brain contrasted to the brain changes seen in Alzheimer disease. With our growing geriatric population, we greatly need to increase our understanding of both the causes of human aging and the goals of gerontology and geriatrics and to expand research into the significant problem of Alzheimer disease.

T cell potentiation by low dose ionizing radiation: possible mechanisms.

The phenomenon of a stimulatory response induced by an exposure to a low dose of an otherwise toxic agent has been observed in a wide variety of organisms, ranging from the simplest prokaryotes to higher eukaryotes and with a spectrum of stimuli. This would suggest that the phenomenon is evolutionarily conserved and biologically important. However, we do not understand the mechanism responsible for the phenomenon, although it has been known for over 100 y. A reasonable assumption would be that adequate models and challenging paradigms are lacking to resolve this fundamental problem. Evidence is presented to show that the potentiation of T cell response by exposing them to single or multiple low doses of ionizing radiation is a feasible cellular model to understand the phenomenon. In addition, several possible mechanisms are discussed, including the participation of stress proteins and prostaglandins in stabilizing the signal transducing, transcriptional and translational machineries, and the possible role of a more efficient mechanism of DNA repair.

Immune potentiation after fractionated exposure to very low doses of ionizing radiation and/or caloric restriction in autoimmune-prone and normal C57Bl/6 mice.

Very low doses of ionizing radiation can enhance immune responsiveness and extend life span in normal mice. Total lymphoid irradiation at relatively high doses of radiation can retard autoimmune disease in genetically susceptible mice, but may impair immune function. In order to determine whether fractionated low dose exposure would enhance immune response and retard lymphadenopathy in autoimmune-prone mice, groups of C57B1/6 lpr/lpr mice were sham irradiated, exposed 5 days/week for 4 weeks to 0.04 Gy/day (0.8 Gy cumulative dose), or to 0.1 Gy/day (2.0 Gy cumulative dose). After the radiation protocol, the mice were evaluated for splenic T cell proliferative capacity, T cell subset distribution, and total spleen cell numbers. The independent and additive effect of caloric restriction was additionally assessed since this intervention has been shown to increase immune responsiveness and retard disease progression in autoimmune-prone mice. The congenic C57B1/6 +/+ immunologically normal strain was evaluated in parallel as congenic control. The results indicated that mitogen-stimulated proliferation was up-regulated in both strains of mice after exposure to 0.04 Gy/day. The proliferative capacity was additively enhanced when radiation at this dose level was combined with caloric restriction. Exposure to 0.1 Gy/day resulted in further augmentation of proliferative response in the lpr/lpr mice, but was depressive in the +/+ mice. Although the proportions of the various T cell subpopulations were altered in both strains after exposure to LDR, the specific subset alterations were different within each strain. Additional experiments were subsequently performed to assess whether the thymus is required for LDR-induced immune potentiation. Thymectomy completely abrogated the LDR effect in the +/+ mice, suggesting that thymic processing and/or trafficking is adaptively altered with LDR in this strain. In contrast, augmentation in proliferative activity after LDR in the lpr/lpr mice was maintained, although attenuated, in thymectomized mice. Taken together, these results indicate that fractionated exposure to LDR augments the proliferative response of spleen cells in both autoimmune-prone and immunologically normal mice; however, within each strain, the mechanisms appear to be different.

Immunotoxicity of alcohol in young and old mice. I. In vitro suppressive effects of ethanol on the activities of T and B immune cells of aging mice.

A murine aging model was employed to assess effects of ethanol exposure on the T-cell proliferative response to mitogenic stimulation and on the T cell-dependent primary antibody response to sheep red blood cells (RBC) in vitro. Splenic cells from young (3-5 months) and old (28-32 months) BALB/c mice were first assessed for their ability to produce interleukin (IL) 2 and proliferate in response to mitogenic stimulation in the presence of various doses of ethanol. Then, splenic T blast cells from young and old mice, generated by Con A-activation, were assessed for their IL2-dependent proliferative capacity in the presence of various doses of ethanol. Finally, splenic cells of young and old mice were assessed for their ability to generate plaque-forming cells (PFC) in response to sheep RBC in the presence of various doses of ethanol. The results revealed that ethanol has a much greater suppressive effect on old than young splenic T cells (10-15 times), as judged by their ability to proliferate in response to mitogenic stimulation. However, the magnitude of the difference in the suppressive effect is less when the cells are cycling (2 times). Furthermore, ethanol had only a minimal suppressive effect on IL2 production by T cells of both young and old mice, even at the concentration of 100 mM. These findings would suggest that the ethanol-mediated suppression of T cell proliferation of both young and old mice is more likely due to an impairment of metabolic event(s) associated with or subsequent to the interaction of IL2 and IL2 receptor leading to cellular replication.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of cutaneous delayed-type hypersensitivity reaction and T cell proliferative response in elderly nursing home patients: an approach to identifying immunodeficient patients.

Clinical experience suggests the delayed-type hypersensitivity (DTH) skin test lacks sensitivity in assessing the integrity of systemic cell-mediated immunity (CMI) or the status of recent or remote mycobacterial infections in elderly nursing home residents. In an attempt to clarify this issue, DTH reaction to purified protein derivative (PPD), tetanus toxoid and Candida albicans was compared with circulating thymus-derived lymphocyte (T cell) proliferation (TCP) to stimulation with PPD and anti-CD3 antibody in 24 randomly selected nursing home residents. The DTH reaction and the TCP response correlated reasonably well among the DTH reactors but poorly among DTH nonreactors, suggesting there may be age-related immunologic changes in the skin itself. Also, the DTH skin test to PPD alone was found to be a poor index of the integrity of systemic CMI.

Changes in serum levels of Forssman-like antibody in patients with gastric cancer.

Because Forssman antigen, one of the most well-known heteroantigens, has been noted in certain cancerous tissues, it would seem that the serum levels of the Forssman antibody of patients with these cancers would be low, owing to the absorption of the naturally occurring antibody by the Forssman antigen-containing cancerous tissues. This hypothesis was tested by researchers assessing the serum hemolysin titers of 174 patients with cancer (gastric cancer, 100; colonic cancer, 40; and other cancers, 45) and of 856 age-matched, sex-matched, and blood type-matched healthy individuals against the serum levels of sheep red blood cells. Serum levels of the hemolysin of patients with gastric cancer tend to be lower than those of patients with other types of cancer and also lower than those of age-matched and sex-matched controls. The decrease was especially prominent in patients with moderately differentiated adenocarcinoma of the stomach. Preoperative and postoperative serum samples of 40 patients with gastric cancer were analyzed therefore to determine the effect of surgically removing the cancer on the serum level of the hemolysin. The results showed that the serum levels of the hemolysin antibody increased in all 40 patients after the successful surgical removal of the cancer. However, in patients with recurrence of the cancer, the serum levels of hemolysin decreased again in 11 of 11 patients. These results indicate that the serum levels of the Forssman-like hemolysin could be used as an index of recurrence in patients with gastric cancer after surgical removal of the cancer.

The effect of exercise on natural killer cell activity in young and old subjects.

Alterations in immune function have been commonly reported in elderly persons. We have examined the effect of age on the responsiveness of natural killer (NK) cells to in vitro stimulation with recombinant interleukin-2 (rIL-2) and in vivo stimulation with exercise in 17 healthy subjects (8 young and 9 old). The old subjects were found to have NK cell numbers and function that were not significantly different from the young subjects at baseline. They also responded as well as the young subjects to rIL-2 stimulation of NK cells in vitro. In response to maximal bicycle ergometry exercise, there was a marked rise in NK activity in the old (7.52 +/- 1.71 LU/10(6) pre-exercise vs 15.20 +/- 3.27 LU/10(6) post-exercise, p less than .03) and the young (6.29 +/- .48 LU 10(6) vs 14.56 +/- 1.86 LU 10(6), p less than .005) subjects. Lymphocytes bearing the NK marker Leu 11a also rose significantly post-exercise in both old and young subjects. We conclude that healthy elderly subjects increase their NK activity in response to the acute stressor, exercise, at least as effectively as do young subjects.

Preferential enhancement by 2-mercaptoethanol of IL-2 responsiveness of T blast cells from old over young mice is associated with potentiated protein kinase C translocation.

Certain thiol compounds have been shown to enhance the T cell-dependent immune response of mice in vivo and the proliferation of T cells in vitro. The magnitude of augmentation is often greater in old than young mice. We hypothesized that the metabolic process that is preferentially up-regulated by thiol compounds in T cells from old mice may reflect a rate-limiting process which contributes to immunosenescence in aging mice. Because IL-2 dependent T cell proliferation in vitro is positively correlated with the strength of T cell-dependent immune response in vivo, we investigated the effects of 2-ME on (a) IL-2 synthesis in vitro, (b) the IL-2-IL-2R binding interaction, and (c) the translocation of PKC from the cytosol to the membrane in Con A-activated splenic T cells from young and old C57BL/6 and C57BL/s mice. The results demonstrated that 2ME does not preferentially enhance the synthesis or secretion of IL-2. Neither the binding affinity of IL-2 to the IL-2R nor the number of receptors on activated T cell blasts differed between young and old mice. At the post-receptor binding level, the magnitude of the translocation of PKC from the cytosol to the membrane was significantly greater in the T blast cells from old than young mice. The preferential enhancement of IL-2-dependent proliferation of T cells from old mice by 2ME is therefore associated with a potentiated translocation of PKC. This would suggest that the metabolic event involved in the translocation of PKC in T cells is vulnerable to aging.