In situ hybridization analysis of the age-associated decline in IL-2 mRNA expressing murine T cells

Age-Related Changes in Thymic Central Tolerance

Thymic epithelial cells (TECs) and hematopoietic antigen presenting cells (HAPCs) in the thymus microenvironment provide essential signals to self-reactive thymocytes that induce either negative selection or generation of regulatory T cells (Treg), both of which are required to establish and maintain central tolerance throughout life. HAPCs and TECs are comprised of multiple subsets that play distinct and overlapping roles in central tolerance. Changes that occur in the composition and function of TEC and HAPC subsets across the lifespan have potential consequences for central tolerance. In keeping with this possibility, there are age-associated changes in the cellular composition and function of T cells and Treg. This review summarizes changes in T cell and Treg function during the perinatal to adult transition and in the course of normal aging, and relates these changes to age-associated alterations in thymic HAPC and TEC subsets.

Influence of age on behavioral, immune and endocrine responses to the T-cell superantigen staphylococcal enterotoxin A

Aged subjects are more vulnerable to administration of the endotoxin lipopolysaccharide, but research on age-associated sensitivity to other immune stimulants has been limited. The current study examined the effects of administering the superantigen, staphylococcal enterotoxin A (SEA), to young (4-month-old) and aged (20-month-old) male C57BL/6J mice on consumption of a novel liquid, cytokine production, corticosterone levels, and expression of central mRNA levels of cytokines and corticotropin-releasing hormone. SEA produced exaggerated hypophagia in aged mice, as they showed decreased consumption that persisted for 24 h. SEA increased hypothalamic mRNA levels of interleukin-1beta in the aged, but not the young, mice 2 h after administration. No differences in cytokine expression were observed 24 h after SEA. Both age groups showed increased plasma corticosterone levels 2 h after SEA administration. However, 24 h after SEA exposure the aged, but not the young, mice showed an augmented corticosterone response to the consumption test. Collectively, these data show that aging may exacerbate the behavioral and neuroinflammatory response to superantigen exposure. Further, the present study suggests that immune activation may result in delayed alterations in stress-induced corticosterone production in aged subjects.

Antioxidants, cytokines, and influenza infection in aged mice and elderly humans

The age-associated dysregulation of the immune response contributes to higher incidences of infectious diseases in the aged. Of note, there is dysregulation of cytokines, including a change in T helper (Th) 1/Th2 cytokine balance and an increase in production of proinflammatory cytokines. Synthesis of many cytokines is influenced by changes in the cellular oxidant/antioxidant balance. Because vitamin E supplementation reduces oxidative stress and improves the immune response in the aged, a series of experiments was conducted to determine the effect of supplementation with vitamin E and other antioxidants on resistance to influenza infection in aged mice and the role of cytokines in vitamin E-induced increase in resistance to influenza infection. The results of these studies plus findings by other investigators on the effects of age and antioxidants on production of cytokines in human and animal models are reviewed.

Aging and T-cell-mediated immunity

Changes in the T-lymphocyte compartment represent the most critical component of immunological aging. Recent studies have demonstrated that the age-related decline in T-cell-mediated immunity is a multifactorial phenomenon affecting T-cell subset composition as well as several proximal events such as protein tyrosine phosphorylation, generation of second messengers, calcium mobilization and translocation of protein kinase C, and distal events such as lymphocyte proliferation and cytokine production of the T-cell activation pathway. Age-related T-cell immune deficiency is preceded by thymic involution and is influenced by several intrinsic as well as extrinsic factors. Further, the role of monocytes and macrophages in T-cell activation changes with advancing age. This brief review will summarize the current knowledge of the cellular as well as molecular aspects of immunodeficiency of T cells due to aging, some of the paradoxes of aging as related to T-cell-mediated immunity, and possible factors which contribute to this paradox. Finally, experimental approaches will be suggested that might resolve these controversies and that might provide insights into the diverse and complex mechanisms that contribute to immunodeficiency of T cells. Ultimately these studies may suggest possible therapeutic interventions to enhance immune function in the elderly.

The increase in the induction of IL-2 expression with caloric restriction is correlated to changes in the transcription factor NFAT

The objective of this study was to determine if the increase in the induction of interleukin-2 (IL-2) expression with caloric restriction correlates with changes in binding activity of the IL-2-specific transcription factor NFAT (nuclear factor of activated T cells) and/or the ubiquitous transcription factor AP-1 in T cells from male Fischer 344 rats. Splenic T cells were isolated from young (6-month) and old (24-month) rats fed ad libitum and from old (24-month) rats fed a restricted diet (40% caloric restriction) that began at 6 weeks of age. T cells were stimulated with concanavalin A (Con A) and the expression of IL-2 and the DNA binding activity of the transcription factors NFAT and AP-1 were measured in these cells. We found that the induction of IL-2 activity and mRNA levels decreased with age and that caloric restriction significantly (P < 0.05) reduced the age-related decline in IL-2 expression. The ability of nuclear extracts from T cells isolated from old rats fed ad libitum and restricted old rats to bind to the NFAT oligonucleotide or AP-1 oligonucleotide decreased with age. Caloric restriction significantly (P < 0.05) reduced the age-related decline in NFAT but had no significant effect on AP-1 binding activity. We also measured the induction of c-fos and c-jun expression by Con A in T cells from young and old rats fed ad libitum or caloric-restricted diet. The induction of c-fos protein and mRNA levels but not c-jun protein or mRNA levels decreased significantly with age. Caloric restriction significantly (P < 0.05) reduced the age-related decline in c-fos expression but had no significant effect on c-jun expression. Therefore, the increase in IL-2 expression with caloric restriction correlates with an increase in binding activity of transcription factor NFAT and an increase in the expression of c-fos, which is a component of the NFAT-protein complex.

Effect of aging on cytokine production in normal and experimental systemic lupus erythematosus afflicted mice

The objective of the this study was to determine the cytokine profile of aging mice and to establish whether changes in cytokine production account for the fact that aging mice develop a milder disease than the young in response to induced experimental systemic lupus erythematosus (SLE). Cytokine secretion was evaluated in groups of BALB/c and C3H.SW mice at different ages between 2 and 24 months. The production of IL-2, IL-4, IL-10, IFN gamma and TNF alpha was determined in supernatants of ConA-stimulated splenocytes and that of IL-1 in the supernatants of LPS-stimulated peritoneal macrophages. A gradual age-related decline was observed in the production of IL-2 and IFN gamma, whereas the levels of IL-4, IL-10, IL-1 and TNF alpha progressively increased with aging, in unimmunized BALB/c and C3H.SW mice. Experimental SLE was induced in 2 and 10 month old C3H.SW mice by immunization with the monoclonal anti-DNA antibody bearing the 16/6 Id. The characteristic cytokine profile following immunization of 2 month old mice was early increased production of TNF alpha and IL-1, followed by a peak of Th1 type cytokines (IL-2, IFN gamma). At a later stage of the disease, a peak of Th2 type cytokines (IL-4, IL-10) was observed that was concomitant with low levels of Th1 cytokines. In contrast, in the 10 month old mice that were immunized with 16/6 Id only a mild increase in all the above cytokines was observed. We suggest that the lower autoantibody production and moderate clinical manifestations in aging mice with experimental SLE are causally related to the decreased production of pro-inflammatory cytokines at the initial stages of the disease followed by a lower production of both Th1 and Th2 type cytokines.

Failure of aged rats to accumulate eosinophils in allergic inflammation of the airway

To investigate the effect of aging on the allergic airway response, we examined the bronchoconstrictive responses and cellular inflammatory changes in a rat model of bronchial asthma by evaluating young and old animals. Two different age groups of Brown-Norway rats, actively sensitized by injection of ovalbumin into the foot pads, were used: 7 to 8 weeks old (young group) and 100 to 120 weeks old (aged group). Both the aged and young rats produced on ovalbumin-specific IgE antibody and exhibited an immediate asthmatic response after exposure to ovalbumin, but the degree of specific IgE antibody was significantly higher in young rats. The young group showed a marked increase in the number of eosinophils and neutrophils in bronchoalveolar lavage fluid 2 days after exposure to ovalbumin, whereas no eosinophilia was seen in the aged group. To evaluate the mechanism of the decreased accumulation of eosinophils in aged rats, cells from popliteal lymph nodes from ovalbumin-sensitized rats were incubated with ovalbumin for 48 hours. Although eosinophil chemotactic activity, determined by a modified Boyden chamber method, was present in the supernatant of cultured lymph node cells from young rats, it was absent from those of aged rats. In vivo administration of anti-IL-5 monoclonal antibody revealed that one of the factors of eosinophil chemotactic activity was IL-5. Lymph node cells from aged rats tended to produce greater amounts of interferon-gamma than did those from young animals. Findings indicate that aged rats have a defect in eosinophil accumulation in sites exposed to antigen, probably because of an age-dependent alteration in T cells.

The effect of age on the expression of interleukin-2

Interleukin-2 (IL-2) is a growth promoting cytokine that has received a great deal of attention over the past decade with respect to aging and cancer. It is produced primarily by helper T cells and regulates the growth and function of various cells that are involved in cellular and humoral immunity. The expression of IL-2 has been found to decrease with age in humans and rodents. The decline in IL-2 production has been shown to parallel the age-related decrease in immunologic function. Several studies indicate that treatment of lymphocytes from old subjects with exogenous IL-2 or infusion of IL-2 into old animals partially or completely restores some of the immune functions that decline with age. The age-related decline in IL-2 production has been shown to arise from a decline in IL-2 transcription, and a recent study suggests that the transcription factor NFAT (nuclear factor of activated T cells) may play a role in the decline in IL-2 transcription.

Modulation of antioxidant activities and immune response by food restriction in aging Fisher-344 rats

Food restriction delays the loss of several cellular immune functions, retards the onset of many diseases during aging and, consequently, extends life span significantly in laboratory rodents. The present study was undertaken to determine whether the age-associated loss in immune function is linked to changes in microsomal and mitochondrial membranes of spleens in Fischer-344 (F-344) male rats. In this study, we determined cytosolic superoxide dismutase activity (SOD), fluidity and cholesterol content in the splenic microsomal and mitochondrial membranes, and DNA synthesis and IL-2 production in spleen cells from young and old ad libitum-fed (AL) and food restricted (FR) rats. The results show that proliferative response to phytohemagglutinin (PHA) and concanavalin A (Con-A) was significantly higher in the spleen cells of 18-month- and 24-month-old FR rats, as compared to their age-matched AL controls. Cytosolic SOD activity in the 24-month-old AL rats decreased by 28% as compared to 6-month-old AL rats, whereas in FR old rats, the loss was only 12%, suggesting that food restriction prevents loss in cytosolic SOD activity in spleens. Our data are consistent with the notion that food restriction modulates loss in immune response of splenocytes by maintaining both cytosolic SOD activity and membrane fluidity during aging.

Geriatric research, education and clinical centers: their impact in the development of American geriatrics

The GRECC program was established by the VA in 1975 and has been expanded since then to 16 sites. For more than a decade, GRECC staff have made major contributions to advancing the understanding of the aging process and developing approaches that have improved the care of older veterans as well as all frail elderly persons in the United States. Most notably, GRECC staff have been among the leading scientists in the field of aging, have stimulated the growth of some of the highest quality university-based geriatric programs in the country, have provided clinical training in geriatrics to thousands of health professional students and practitioners, and have developed innovative models of geriatric care. The GRECC model of integrating research, education, and clinical activities in a "center of excellence" with specific goals and expectations serves as one of the best examples of how scientific advances can be applied effectively to direct patient care.

Cell mediated immunity changes in ageing, relative importance of cell subpopulation switches and of nutritional factors

Decreased T-cell functions with ageing have been extensively described. This review focuses on recent data on changes in T-cell subpopulations related to ageing and their consequences on T-cell proliferation. Increase of immature T cells CD2+ CD3- is an ageing phenomenon related to T-cell declining proliferation. Recently it was shown that increase of immature T cells was due to an increase in different subtypes of the CD2+ CD3- population, double-negative CD2+ CD4- CD8- and double-positive CD2+ CD4+ CD8+ subpopulations, the former being associated with nutritional deficit, the latter with associated diseases. Other authors have focused on decreases of native T cells with parallel increase of memory T cells; such a switch is also relevant to declining T-cell proliferation. This review focuses on two major factors which influence immune ageing; nutritional parameters and antigen exposure.

Age-related changes in production of interleukin-7 (IL-7) by murine long-term bone marrow cultures (LTBMC)

Age-related decreases in humoral immune function have been well documented. In aged mice, these functional deficits may be due, in part, to decreased numbers of precursor B cells. Interleukin-7 (IL-7) plays a key role in B cell development by stimulating proliferation of progenitor and pre-B cells. In the current study, proliferation of the murine IL-7-dependent pre-B cell line SCID/FC-7 (SCID) was used to assess IL-7 activity in long-term bone marrow culture-conditioned medium (LTBMC-CM) from both young (4-8-week-old) and older (16-40-week-old) mice. Time to reach peak production and peak IL-7 levels were similar in both groups and was optimal between weeks 2 and 6 of culture. IL-7 activity in LTBMC-CM from older mice fell rapidly to negligible levels after 8 weeks in culture. These findings are consistent with age-related changes in stem cell production and B lymphopoiesis in LTBMC reported in other studies.

Expression of heat shock protein 70 is altered by age and diet at the level of transcription

Because heat shock proteins have been shown to play a critical role in protecting cells from hyperthermia and other types of physiological stresses, it was of interest to determine what effect age and caloric restriction have on the ability of cells to regulate the expression of heat shock protein 70 (hsp70), the most prominent and most evolutionarily conserved of the heat shock proteins. Caloric restriction is the only experimental manipulation known to retard aging and increase survival of mammals. The ability of hepatocytes isolated from young/adult (4- to 7-month-old) and old (22- to 28-month-old) male Fischer F344 rats fed ad libitum or a caloric restriction diet (60% of the content of the ad libitum diet) to express hsp70 was determined after a mild heat shock (42.5 degrees C for 30 min). We found that the induction of hsp70 synthesis and mRNA levels by heat shock was 40 to 50% lower in hepatocytes isolated from old rats than in hepatocytes isolated from young rats. Using in situ hybridization, we found that essentially all hepatocytes from the young/adult and old rats expressed hsp70 in response to heat shock; therefore, the age-related decrease in the induction of hsp70 expression was not due to an age-related accumulation of cells that do not respond to heat shock. Measurements of hsp70 mRNA stability and hsp70 transcription demonstrated that the age-related decline in hsp70 expression arose from a decline in hsp70 transcription. Interestingly, the age-related decline in the induction of hsp70 expression was reversed by caloric restriction; e.g., the induction of hsp70 synthesis, mRNA levels, and nuclear transcription were significantly higher in hepatocytes isolated from old rats fed the caloric restricted diet than in hepatocytes isolated from old rats fed ad libitum. The levels of the heat shock transcription factor in nuclear extracts isolated from heat-shocked hepatocytes were measured in a gel shift assay. Binding of the heat shock transcription factor to the heat shock element decreased with age and was significantly higher in hepatocyte extracts isolated from old rats fed the caloric restriction diet than in those from old rats fed ad libitum. Thus, our study demonstrates that the ability of hepatocytes to respond to hyperthermia and express hsp70 decreases significantly with age and that this decrease occurs at the transcriptional level. In addition, caloric restriction, which retards aging, reversed the age-related decline in the induction of hsp70 transcription in hepatocytes.

Expression of heat shock protein 70 is altered by age and diet at the level of transcription

Because heat shock proteins have been shown to play a critical role in protecting cells from hyperthermia and other types of physiological stresses, it was of interest to determine what effect age and caloric restriction have on the ability of cells to regulate the expression of heat shock protein 70 (hsp70), the most prominent and most evolutionarily conserved of the heat shock proteins. Caloric restriction is the only experimental manipulation known to retard aging and increase survival of mammals. The ability of hepatocytes isolated from young/adult (4- to 7-month-old) and old (22- to 28-month-old) male Fischer F344 rats fed ad libitum or a caloric restriction diet (60% of the content of the ad libitum diet) to express hsp70 was determined after a mild heat shock (42.5 degrees C for 30 min). We found that the induction of hsp70 synthesis and mRNA levels by heat shock was 40 to 50% lower in hepatocytes isolated from old rats than in hepatocytes isolated from young rats. Using in situ hybridization, we found that essentially all hepatocytes from the young/adult and old rats expressed hsp70 in response to heat shock; therefore, the age-related decrease in the induction of hsp70 expression was not due to an age-related accumulation of cells that do not respond to heat shock. Measurements of hsp70 mRNA stability and hsp70 transcription demonstrated that the age-related decline in hsp70 expression arose from a decline in hsp70 transcription. Interestingly, the age-related decline in the induction of hsp70 expression was reversed by caloric restriction; e.g., the induction of hsp70 synthesis, mRNA levels, and nuclear transcription were significantly higher in hepatocytes isolated from old rats fed the caloric restricted diet than in hepatocytes isolated from old rats fed ad libitum. The levels of the heat shock transcription factor in nuclear extracts isolated from heat-shocked hepatocytes were measured in a gel shift assay. Binding of the heat shock transcription factor to the heat shock element decreased with age and was significantly higher in hepatocyte extracts isolated from old rats fed the caloric restriction diet than in those from old rats fed ad libitum. Thus, our study demonstrates that the ability of hepatocytes to respond to hyperthermia and express hsp70 decreases significantly with age and that this decrease occurs at the transcriptional level. In addition, caloric restriction, which retards aging, reversed the age-related decline in the induction of hsp70 transcription in hepatocytes.

Explanations for reduced tumor proliferative capacity with age

Tumors in general occur more frequently in older people, but many of the common tumors appear to be less malignant in older hosts. In this article mechanisms of tumor enhancement are reviewed, and those that are age-sensitive are emphasized. In this regard, our earlier experimental work suggested that age-associated immune change (immune senescence) is most important in explaining reduced tumor growth. We have found that unstimulated spleen cells in culture produce a tumor-enhancing factor (TEF) that enhances B16 murine melanoma cell proliferation. TEF, and others, such as lymphocyte-induced angiogenesis factor (LIA) and various other autocrine growth factors, may stimulate malignant cells in cancer-bearing hosts. An age-associated reduction in those factors could account for the observed reduced tumor growth and spread in hosts of advanced age.

The effect of age on mitogen responsive T cell precursors in human beings is completely restored by interleukin-2

It is well known that the function of T lymphocytes is significantly impaired by advancing age. In the present study, attempts have been made to further characterize the T cell impairment of elderly subjects. Thus, we have performed limiting dilution microculture analysis to evaluate the precursor frequency of T lymphocytes responding to a mitogenic stimulus in old and young subjects. Furthermore we have evaluated the activity of recombinant interleukin-2 (rIL-2) on these cells. The results demonstrate that in older subjects the frequency of these precursors is significantly decreased. The in vitro treatment with rIL-2 increased the frequency of mitogen responsive T lymphocyte precursors in both groups so that the difference between the two groups was not significant. Thus present results extend the findings demonstrating that older subjects display an impairment of T cell functions and that IL-2 treatment may correct these alterations. In particular, they confirm the hypothesis that age-associated functional changes are more likely due to diminished numbers of reactive cells, than to a decline in the activity of all cells.

Age- and strain-related differences in murine spleen cell responses to different activation signals

The effect of age on the response of splenocytes to activation with anti-CD3 mAb and a combination of anti-CD3 mAb and TPA, as evidenced by interleukin-2 (IL-2) and interleukin-4 (IL-4) production and cell proliferation, was examined in the C57BL/6 and DBA/2 murine strains. Depending on the mode of activation, there were age and strain differences in IL-2 and IL-4 production. With all modes of activation, cells from the old C57BL/6 mice produced less IL-2 than their young counterparts. In DBA/2 mice there was no age-related difference in IL-2 production with anti-CD3 mAb activation alone, whereas when the same cell population was activated with anti-CD3 mAb and TPA an age-associated decrease in IL-2 production occurred. In both strains, there was an age-related increase in IL-4 production with anti-CD3 mAb activation. After addition of TPA, however, there was an age-related decrease in IL-4 production. An age-related decline in the proliferation occurred with all modes of activation in both mouse strains. There were also strain-related differences in proliferation after the addition of forskolin, an inhibitor of Th1-cell function. While forskolin inhibited the proliferation of cells from the young C57BL/6 mice only, in the DBA/2 mice proliferation of cells was inhibited in both age groups. There were no strain-related differences in inhibition by anti-transferrin receptor (TrfR) mAb, although cells from the old mice were slightly more sensitive to this inhibition.

Splenic and inguinal lymph node T cells of aged mice respond differently to polyclonal and antigen-specific stimuli

Numerous changes have been reported to occur in T cell responsiveness of mice with increasing age. However, most of these studies have examined polyclonal stimulation of spleen cells from a limited number of mouse strains. This study investigated the influence of genetic background, source of lymphocytes, and type of stimulus on age-associated changes in T cells response. Con A-induced proliferation and IL-2 and IFN-gamma production by splenic lymphocytes (SL) was significantly greater in CBA/Ca mice compared to C57BL/6 mice, regardless of age. SL of both strains exhibited the predicted age-dependent decline in proliferative response and an increase in IFN-gamma production in response to Con A. In contrast, however, only SL from C57BL/6 mice demonstrated the predicted age-dependent decline in Con A-induced IL-2 production; Con A-induced SL of young and aged CBA/Ca mice produced comparable amounts of IL-2. Differences in age-associated responses to Con A were also observed between SL and inguinal lymph node (ILN) cells of CBA/Ca mice. In contrast to SL, ILN cells demonstrated an increased proliferative response to Con A. However, lymphokine production by Con A-stimulated ILN cells from aged CBA/Ca mice was similar to that of Con A-stimulated SL from aged CBA/Ca mice. To determine if aged ILN T cells respond similarly to polyclonal and antigen-specific stimuli, keyhole limpet hemocyanin (KLH) responses of T cells isolated from ILN of aged and young CBA/Ca mice were examined. KLH-specific T cells from aged mice cultured with KLH-pulsed macrophages (M phi) from aged mice were significantly reduced in their ability to proliferate compared to KLH-specific T cells of young mice cultured with young KLH-pulsed M phi. In contrast to the expected results, the defect was not at the level of the T cells; proliferation of young T cells cultured with aged KLH-pulsed M phi was equivalent to the proliferation of aged T cells cultured with aged M phi. These results suggest that aging has differential effects on polyclonal and antigen-specific T cell proliferation and on polyclonal stimulation of T cells isolated from different lymphoid organs and from different strains of mice.

Cell proliferation and cytokine production by CD4+ cells from old mice

Splenocytes from young adult or old C57BL/6NNia mice were stimulated in vitro with the anti-CD3 epsilon mAb, 145-2C11, in either soluble (2C11s) or plate-bound (2C11i) form. In the young group, each mode of cell activation resulted in peak DNA synthesis at approximately 48 h of culture; at this time point, the old group exhibited response levels to 2C11s or 2C11i that were approximately 40% of those in the young group. However, in the presence of 2C11i, splenocytes from old donors showed a delayed peak response which approached the peak levels attained in the young group. To analyze the responsiveness of the CD4+ T cell subpopulation, this cell type was isolated from spleens of young or old mice and was stimulated in vitro with 2C11s or 2C11i, in the presence or absence of added accessory cells (T cell-depleted, irradiated splenocytes). The induction of DNA synthesis by 2C11s was accessory cell dependent, and the response in the old group were markedly reduced in comparison to those in the young group. In contrast, stimulation of DNA synthesis with 2C11i was relatively accessory cell independent, resulted in higher response levels in both age groups, and lessened the disparity between age groups. The analysis of IL-2 and IL-4 secretion by stimulated CD4+ cells revealed that, in response to 2C11s and accessory cells, only IL-2 accumulation was detectable and the levels in the young group were approximately 10-fold higher than the IL-2 levels in the old group. However, stimulation of CD4+ cells with 2C11i and accessory cells yielded improved IL-2 production and a detectable IL-4 response in the old group, whereas the young group exhibited a response profile similar to that induced by 2C11s. Further analysis of the IL-2, IL-4, and IFN gamma mRNA levels in 2C11i-stimulated CD4+ cells revealed that old donor cells accumulated similar levels of IL-2 transcripts, but higher levels of IL-4 and IFN gamma transcripts, than young donor CD4+ cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of aging on host defences. Implications for therapy

Immunosenescence is a well known physiological phenomenon resulting from reduced efficiency of the immune system in the elderly. It has been studied both in animal models and in humans. In this review attention is focused on T cell responsiveness, since this cell type is both a marker of the immune response and one of the main targets of several drugs. For this latter reason, most studies of the effect of drugs on the immune system have been performed with reference to the effects on T lymphocytes. In the second part of the article experimental data concerning several drugs and drug classes [steroids, calcium antagonists, theophylline, histamine H1- and H2-receptor antagonists, sodium cromoglycate (cromolyn sodium), pirenzepine, rosaprostol, beta 2-mimetics, antibiotics and antibacterials] and immune responsiveness are reviewed. Lastly, the clinical perspectives of pharmacological treatment in aged subjects in relation to immunosenescence are evaluated.

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.

Aging and immune function

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

Age-related decrement in cytotoxic T lymphocyte (CTL) activity is associated with decreased levels of mRNA encoded by two CTL-associated serine esterase genes and the perforin gene in mice

The age-related decline in cytotoxic T lymphocyte (CTL) activity has been recognized for many years. Age-related alterations in several immunologic events have been suggested to be partly or completely responsible for this decline. We had previously demonstrated (Bloom et al., Cell. Immunol. 1988. 144: 440) in mice that a deterioration in the lytic mechanism may be at least in part responsible for the decline in CTL activity. We now report that this decline correlates with an age-related decrease in serine esterase activity released into the supernatant medium in the process of generating CTL. Northern analyses were then used to examine the effect of age on expression of genes encoding for perforin and two CTL-associated serine esterases. The products of all three of these genes have all been postulated to play roles in CTL-mediated lysis. We show that the expression of all three of these genes appears to decline with age in the process of generating allogeneic CTL. These alterations in gene expression correlated both with diminished cytolytic and released esterase activities generated by mixed leukocyte culture in spleen cells of old mice compared to young. The age-related decline in gene expression could not be attributed to shifts in T cell subsets, but CD8+ cells generated by allogeneic stimulation of nylon wool-passed spleen cells from old mice expressed significantly less cytolytic activity than those from young. This report is the first demonstration of an age-related decrease in expression of a functionally related group of genes. In addition, these findings are compatible with the suggested roles for perforin and serine esterase release in CTL-mediated target cell lysis.

In vivo immunologic intervention in age-related T cell defects in murine gut-associated lymphoid tissues by IL2

Our recent studies indicate that the aging process impairs gut mucosal humoral immune responses to mycobacterial antigen (Ag), largely owing to defects in T cell function--in particular, that of suppressor T cells. To correct the age-associated Ag-specific T cell-mediated immune alteration recombinant IL2 (50,000 units/s.c./mouse/day) was administered for 3 weeks to the aged (greater than 24 months) mice (BALB/c), which were divided into 4 groups (Gr) [Gr. 1, fed intragastrically (i.g.) with saline; Gr. 2, immunized i.g. with Mycobacterium paratuberculosis (M. paratbc) protoplasmic Ag; Gr. 3, administered IL2 alone; Gr. 4, immunized i.g. with the Ag and given IL2]. In addition, young adult mice were also grouped and treated as the aged. First, we examined the effect of exogenous IL2 on Ag-specific immunoglobulin (Ig) production by gut-associated lymphoid tissues (GALT) (Peyer's patches, PP; mesenteric lymph nodes, MLN) and non-GALT (spleen, SPN) cells. Aged Gr. 4 (treated with both Ag and IL2) GALT and SPN unfractionated cells showed significantly reduced production of Ag-specific IgM, IgG, and IgA, as compared to aged Gr. 2 (treated with Ag alone) cells. Second, in co-culture experiments with aged T and B cells, aged GALT-derived CD8+ suppressor T (Ts)-depleted T cell subsets of Gr. 4 helped Ag-specific IgM and IgA production by GALT B cells, but to a slightly lesser extent, than those of the Gr. 2. GALT CD4+ T cells of aged Gr. 4 augmented IgM and IgA production by GALT B cells nearly to the levels of the corresponding cocultures of the Gr. 2. In contrast to aged Gr. 2 cocultures, GALT CD4+ plus CD8+ cells of aged Gr. 4 decreased IgM and IgA production to a considerable extent, and in those of SPN, IgG production was also diminished. The humoral immune responses of aged unprimed Gr. 1 (treated with saline) and Gr. 3 (treated with IL2 alone) GALT and SPN cells remained almost unchanged. Similarly, in all Gr. from young adult mice, oral tolerance was maintained regardless of IL2 administration. Third, together with the deletion experiments of the Ts cells, the results of the cross experiments, in which the young adult B and CD4+ Th cells and aged CD8+ Ts cells were cocultured, clearly support the view that the corrective mechanism of the humoral immune responses in aged GALT by exogenous IL2 is attributed to the partial recovery of the Ts cell functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Impairment of CD3-dependent and CD3-independent activation pathways in CD4+ and in CD8+ T cells from old CBA/RIJ mice

Stimulation of T cells from old mice with anti-CD3 antibodies resulted in a high variability of proliferative responses, which were 2- to 8-fold lower than the responses by T cells from young mice, even in the presence of exogenous rIL-2. Moreover, the CD4+ T cells from these old mice displayed a diminished capacity to produce IL-2 in response to anti-CD3. A partial explanation was found in the observation that T cells from the majority of old mice displayed a diminished expression of CD3 of variable intensity. However, after stimulation of the T cells with the combination of phorbol-12-myristate-13-acetate (PMA) and ionomycin to bypass CD3, 3 out of 6 old mice still exhibited 2-fold lower proliferative responses than T cells from young mice; IL-2 production by the CD4+ T cells was lower in all old mice tested. Comparison of CD4+ T cells and CD8+ T cells from old mice revealed a defective PMA/ionomycin response in both subsets, although this defect seemed more pronounced in CD4+ T cells when compared with the young counterparts. The diminished response of CD8+ T cells was accompanied by a diminished expression of the IL-2R alpha-chain. In contrast, old CD4+ T cells expressed rather higher levels of IL-2R alpha-chain than young CD4+ T cells. Altogether, multiple defects which are not necessarily the same in CD4+ and CD8+ T cells are responsible for defective T cell responses in old mice.

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)

T cell activation in the elderly: evidence for specific deficiencies in T cell/accessory cell interactions

We studied T cell activation in the healthy aged (greater than 70 years) by examining lymphocyte proliferative responses to various mitogenic stimuli in accessory cell (AC)-dependent and AC-independent systems. Results show that despite a near normal response to the anti-CD3 monoclonal antibody (mAb) OKT3, peripheral blood mononuclear cells (PBM) from the elderly exhibit a profound reduction in phytohaemagglutinin (PHA)-responsiveness (approximately 30% of young adults). This deficit becomes even more severe at suboptimal doses of PHA. Adding exogenous interleukin-2 (IL-2) or pretreating the AC population with gamma interferon (IFN-gamma) returns the level of proliferation to that seen with young adults. Furthermore, replacing "old" AC with AC from young adults or with U937 (a monocytic cell line) in T cell/AC cell-mixing experiments restores PHA-responsiveness in 70% of cases. On the other hand, AC from the aged fully support PHA responses in T cells from young adults. In AC-depleted cultures, purified T cells from the aged respond normally to the co-mitogenic stimuli, PHA + PMA. Taken together, these results suggest that the age-associated diminution in PHA-responsiveness is due, at least in part, to specific deficiencies in T cell/AC communication.