The effect of age on the expression of interleukin-2

L-deprenyl-induced increase in IL-2 and NK cell activity accompanies restoration of noradrenergic nerve fibers in the spleens of old F344 rats

Previously, we have hypothesized a causal relationship between some measures of immunosenescence and the age-related decline in sympathetic noradrenergic (NA) nerve fibers in spleen and lymph nodes of F344 rats. In the present study, we investigated this interrelationship further by measuring NK cell activity, Con A-induced IL-2 production, norepinephrine (NE) concentration, and morphological localization of NA and neuropeptide-Y (NPY) nerve fibers in the spleens of old (21 months old) male F344 rats after 10 weeks of daily treatment with low doses of L-deprenyl, an irreversible monoamine oxidase-B inhibitor, followed by a 9-day wash-out period. NK cell activity and Con A-induced IL-2 production were increased in deprenyl-treated old rats in comparison to untreated and saline-treated old rats. Deprenyl treatment did not alter the percentage of CD5+ T-cells, but moderately increased the percentage of sIgM+ B-cells in the spleens of old rats. In addition to changes in immune responses, NE content and the volume density of NA and NPY nerve fibers were partially augmented in the spleens of deprenyl-treated old rats. In a separate study, various concentrations of deprenyl were added in vitro to spleen cells from young and old F344 rats to examine the direct effects of the drug on Con A-induced IL-2 production. In contrast to in vivo treatment, in vitro addition of deprenyl did not alter the Con A-induced IL-2 production by splenocytes from old rats. Together, these results suggest that the ability of deprenyl to enhance certain immune responses are interlinked to the restoration of sympathetic NA and NPY nerve fibers in the spleens of old rats.

Transcriptional activation and redox regulation of the tumor necrosis factor-alpha promoter in human T cells: role of the CRE/kappa3 promoter region

Aberrancies in T cell expression of tumor necrosis factor-alpha (TNF-alpha) are frequently observed in inflammatory states characterized by oxidative stress due to excessive generation of hydrogen peroxide (H2O2) and other reactive oxygen species (ROS). In this study, we examined the possible effects of oxidative stress on the expression of TNF-alpha protein and transcriptional activation of the TNF-alpha promoter in human T cells. Results show that exposure of resting T cells to micromolar concentrations of H2O2 did not induce TNF-alpha protein production or transcriptional activation of the TNF-alpha promoter. However, oxidative signals resulted in a dose-dependent suppression of TNF-alpha protein production and transcriptional activation in T cells stimulated with the lectin phytohemagglutinin (PHA) and phorbol myristate acetate (PMA). Optimal suppression of TNF-alpha promoter activity was observed when cells were exposed to oxidative stress during early T cell activation, and other experiments demonstrated that the transactivation responses of the TNF-alpha promoter were quite susceptible to inhibition by both oxidative and reducing changes in cellular redox. Furthermore, reporter gene assays with 5' deletion mutants of the TNF-alpha promoter showed that the CRE/kappa3 composite site played a major role in activation of the TNF-alpha promoter by dual stimulatory signals and suppression of the TNF-alpha promoter by oxidative signals. Thus, T cell expression of TNF-alpha at the protein and transcriptional levels is highly regulated by changes in cellular redox, and the CRE/kappa3 composite site is important for both activation and redox regulation of the TNF-alpha promoter.

Intervention in the aging immune system: Influence of dietary restriction, dehydroepiandrosterone, melatonin, and exercise

The decline in immunologic function with age is associated with an increase in susceptibility to infections and the occurrence of autoimmune diseases and cancers. Hence, the restoration of immunologic function is expected to have a beneficial effect in reducing pathology and maintaining a healthy condition in advanced age. A number of therapeutic strategies have been employed to intervene in the aging immune system. This article reviews the effect of dietary restriction (DR), dehydroepiandrosterone (DHEA) treatment, melatonin (MLT) therapy, and exercise on modulating the immune responses and retarding/reducing immunosenescence. DR has been subject to intensive research and is known to be the most efficacious means of increasing longevity, reducing pathology and enhancing immune function. The circulatory levels of the androgenic hormone DHEA and the pineal hormone MLT decrease with increasing age, and this decrease has been correlated with the age-related decline in the immune system. Therefore, the observation that immunosenescence is associated with low levels of DHEA and MLT has provided a rationale for therapeutic intervention. DHEA treatment and MLT therapy both exhibit immunostimulatory actions and preliminary reports indicate that hormonal (DHEA or MLT) substitution therapy reverses immunosenescence in mice. Similarly, exercise in some studies has been shown to enhance the immune response. However, these findings have not been confirmed by other laboratories. Thus, at the present time, it is difficult to draw any definitive conclusions on the efficacy of DHEA, MLT, and exercise on reversing or restoring the aging immune system.

Signalling into the T-cell nucleus: NFAT regulation

The nuclear factor of activated T cells (NFAT) plays an important role in T-cell biology. Activation of T cells results in the rapid calcineurin-dependent translocation of NFAT transcription factors from the cytoplasm to the nucleus. This translocation process coupled to the subsequent active maintenance of NFAT in the nucleus compartment is critical for the induction of expression of several genes encoding cytokines and membrane proteins that modulate immune responses. The molecular cloning of the NFAT family of transcription factors has facilitated rapid progress in the understanding of the signalling mechanisms that control the activity of NFAT.

Effect of age and dietary restriction on expression of heat shock protein 70 in rat alveolar macrophages

Dietary restriction (DR) is the only effective experimental manipulation known to retard aging in rodents, and this manipulation has been shown to alter a variety of processes that change with age. However, there is no information on the effect of DR on macrophage Function. In the present study, the effect of aging and DR on the ability of alveolar macrophages (AMs) to express the heat shock gene, hsp70 was studied. AMs were isolated by lavage from the lungs of young (4-6 months) and old (24-26 months) rats fed either ad libitum (AL) or a restricted diet (60% of AL). There was no age-related change in the number of cells recovered from young and old rats fed AL. However, the number of cells recovered from the lungs of the DR rats was reduced, and this decrease was statistically significant in young rats. The expression of heat shock protein 70 (hsp70) was measured by the level of the hsp70 mRNA transcript in total RNA isolated from AMs cultured under two conditions: in suspension and after adherence to plastic. When AMs were incubated at 37 degrees C in suspension, no detectable hsp70 expression was observed; however, hsp70 expression was induced at 37 degrees C when the AMs adhered to the plastic culture dishes. Hsp70 mRNA levels were rapidly induced by heat shock (43 degrees C, 1 h) in AMs cultured both in suspension and on plastic. The induction of hsp70 expression did not change significantly with either age or DR in AMs cultured in suspension. In contrast, the induction of hsp70 mRNA levels by AMs adherent to plastic culture plates decreased approximately 70% with age, and hsp70 induction was greater in AMs isolated from DR rats; this difference was statistically significant in young rats. The induction of hsp70 by heat shock (43 degrees C, 1 h) also decreased with age in the adherent AMs, and DR increased the induction of hsp70 expression three- to fourfold in adherent AMs from both young and old rats.

Differential expression of p53 tumor suppressor protein and IL-2 in activated T cells from elderly humans

Aging is associated with a decline in T cell proliferative responses and aberrations in cytokine production. In the present study, we examined if aging might alter the expression of the tumor-suppressor protein p53 and the retinoblastoma susceptibility gene product (Rb) as well as the levels of Bcl-2 in resting and activated human T cells. No significant differences were observed in the basal levels of p53 protein among resting T cells from young and elderly humans. After stimulation with anti-CD3 monoclonal antibody (mAb) OKT3 and phorbol myristate acetate (PMA), T cells from young humans exhibited severalfold increases in p53 protein expression compared with resting T cells. By contrast, T cells from a substantial portion of elderly humans failed to demonstrate significant increases in p53 in response to anti-CD3 plus PMA. No age-related alterations in the levels of Rb or Bcl-2 proteins were observed in resting or anti-CD3/PMA-stimulated T cells. To delineate whether the age-related reductions in p53 expression might be linked to decreased interleukin-2 (IL-2) production, we compared the expression of p53 and IL-2 in anti-CD3/PMA-stimulated T cells from elderly people. The results showed that impaired induction of p53 expression in activated T cells from certain elderly people could be observed without considerable impairments in IL-2 production. These observations suggest that age-related reductions in T cell expression of p53 may contribute to the decline of T cell competence independent of the impairments in IL-2 production.

Activation of p21ras/MAPK signal transduction molecules decreases with age in mitogen-stimulated T cells from rats

Signal transduction is ubiquitously involved in the initiation of physiological signals that lead to growth and proliferation of cells. The signaling cascade mediated by the mitogen-activated protein kinase (MAPK) is considered essential for T cell growth and function. Therefore, it was of interest to determine the influence of age on the induction of MAPK in mitogen-activated T cells. T cells from young (4-6 months) and old (24-26 months) rats responded to concanavalin A (Con A) stimulation by increasing MAPK, c-jun amino terminal kinase (JNK), and p21ras activities. The time course of induction of MAPK/JNK and p21ras activities was similar in T cells isolated from young and old rats. The induction of JNK activity did not change significantly with age; however, the induction of MAPK and p21ras activities was significantly less (50 to 65%) in T cells from old rats than in T cells from young rats. Although the relative protein levels of p42 and p44 MAPK did not change with age, the proportion of the phosphorylated p44 MAPK decreased with age. In addition, it was found that the in vitro kinase activities of the T cell receptor-associated protein tyrosine kinase Lck (p56Lck) and ZAP-70 but not Fyn (p59Fyn) were lower in T cells from old rats than in T cells from young rats. The decline in activities of these signaling molecules with age was not associated with changes in their corresponding protein levels. Thus, our results demonstrate that aging alters the activation of the signal transduction cascade that leads to T cell activation.

Reductions in the activation of ERK and JNK are associated with decreased IL-2 production in T cells from elderly humans stimulated by the TCR/CD3 complex and costimulatory signals

T cells from elderly humans often display impaired IL-2 production, but the mechanisms are unknown. Because the activities of extracellular signal-regulated kinases (ERK) and c-Jun NH2-terminal kinases (JNK) are important for IL-2 production, the current study evaluated if aberrancies in the expression and activation of ERK2 or JNK might underlie decreased IL-2 production by human T cells during aging. The present results show that diminished ERK2 and JNK catalytic activities were commonly detected in T cells from elderly humans stimulated with anti-CD3 mAb OKT3 plus PMA. These reductions did not represent temporal shifts in activation or altered expression of ERK2 or JNK. In addition, the reductions of ERK2 activation in stimulated T cells from elderly individuals were accompanied by decreased Raf-1 kinase activation and could be observed without coexisting impairments in JNK activation. Stimulation of ERK2 activation in elderly T cells correlated with IL-2 production and decreased ERK2 activation was consistently associated with reduced IL-2 production. Although the age-related decreases in JNK activation were accompanied by reduced IL-2 production, substantial impairments of JNK activation were observed with diminished ERK2 activation. Moreover, anti-CD3/PMA-stimulated T cells from elderly individuals that displayed normal JNK activation and impaired ERK2 activation continued to demonstrate reduced IL-2 production. These findings show that impairments in the activation of ERK2 and JNK can accompany decreased IL-2 production by T cells from elderly humans and further suggest that aberrancies in TCR/CD3-dependent activation of the Raf-1/MEK/ERK2 cascade may be rate-limiting for the full induction of IL-2.

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.

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.