Reversal of age-associated decline in immune response to Pnu-imune vaccine by supplementation with the steroid hormone dehydroepiandrosterone

Ajuga remota Benth.: from ethnopharmacology to phytomedical perspective in the treatment of malaria

Treatment and control of malaria have become more difficult with the spread of drug-resistant parasites and insecticide-resistant mosquito vectors. In the search for new antimalarial drugs, ethnopharmacological sources should merit more attention. Establishing the safety of traditional herbal medicines, along with identifying their active principles, are essential steps in the production of a properly standardized and accessible herbal medicine. Phytochemical characterization could also serve as a base for the development of new chemical compounds. The genus of Ajuga belongs to the family Lamiaceae and contains at least 301 species. Many of these plants have been used in traditional medicine. Ajuga remota in particular is traditionally used as a herbal remedy for fever and infections, and is prescribed for malaria by 66% of the Kenyan herbalists. A large number of compounds have already been isolated from A. remota, including ergosterol-5,8-endoperoxide (6), ajugarin-I (1), 8-O-acetylharpagide (5) and several phytoecdysteroids. In vitro pharmacological studies have been conducted on constituents of A. remota of which some of them displayed a concentration-dependent inhibition of chloroquine-sensitive and -resistant Plasmodium falciparum and Mycobacterium tuberculosis. Inhibition of parasitaemia was demonstrated in mouse models with P. berghei, supporting the traditional use of the plant against malaria. In this state-of-the-art review, A. remota as a possible therapeutic tool for malaria is discussed.

Dehydroepiandrosterone as a regulator of immune cell function

Dehydroepiandrosterone (DHEA) is a C19 steroid of adrenal origin. Notably, its secretion declines with age, a phenomenon referred to as the "adrenopause". For many years, the physiological significance of DHEA remained elusive. However, many studies have now shown that DHEA has significant immune modulatory function, exhibiting both immune stimulatory and anti-glucocorticoid effects. Although several of these studies are limited by the fact that they were carried out in rodents, who are incapable of adrenal DHEA production, and therefore have very low circulating levels of this steroid, evidence from the study of immune cells is now accumulating to suggest a role for DHEA in regulating human immunity. This ability to regulate immune function has raised interest in the therapeutic potential of DHEA as a treatment for the immunological abnormalities that arise in subjects with low circulating levels of this hormone. This has included attempts at reversing the impaired immune response of older individuals to vaccination and restoring immune regulation in patients with chronic autoimmune disease. This review summarises the reported effects of DHEA on immune function and discusses the therapeutic potential of this steroid in geriatric medicine and particularly in age-related disease with an immune component.

Dehydroepiandrosterone Sulphate Enhances IgG and Interferon-Gamma Production During Immunization to Tuberculosis in Young But not Aged Mice

Ageing of the endocrine system (endocrinosenescence) has been closely related to immunosenescence. Dehydroepiandrosterone sulphate (DHEAS), a steroid hormone produced by the adrenals with reported enhancing immunomodulatory properties, consistently decline during ageing in parallel to detrimental increase in peripheral glucocorticoids. We investigated here the adjuvant effects of DHEAS during intraperitoneal immunization to Mycobacterium tuberculosis heat shock protein 70 (mycHSP70) in old (24 months) as well as young (3 months) BALB/c mice. Both young and old mice had significantly higher Immunoglobulin G (IgG) levels following immunization. Young mice co-immunized with mycHSP70-DHEAS presented an early increase in specific IgG levels and showed increased Interferon-gamma production compared to old mice. Also, T cells of immunized young animals were consistently more resistant to the immunosuppressive effects of glucocorticoids and to DHEAS. DHEAS was not effective in modulating antigen-specific T-cell proliferation, Interleukin-2 production or percentage of recent activated T-cell subsets (CD4 + CD69 + and CD8 + CD69 +). Our data further indicate mycHSP70 as a putative good antigen in vaccine to tuberculosis. Our data also suggest that DHEAS produced adjuvant effects upon humoral and some cellular immune responses of young, but not old mice and indicate that immunization with DHEAS is capable of changing T-cell responses to steroids.

The unresponsiveness of aged mice to polysaccharide antigens is a result of a defect in macrophage function

A reduction in macrophage (MPhi) function with aging makes mice less responsive to bacterial capsular polysaccharides, such as those present in the pneumococcal polysaccharide vaccine, a model of thymus independent (TI) antigen (Ag). Using trinitrophenol (TNP)-lipopolysaccharide (LPS) and TNP-Ficoll, two other well-studied TI Ag, we studied the mechanistic basis of reduced MPhi function in the aged. We show that aged mice are profoundly hyporesponsive to these TI Ag. As a result of a requirement for MPhi, highly purified B cells from young-adult mice do not respond to TI Ag. When purified, young B cells were immunized with TNP-Ficoll, the antibody production from those cultures reconstituted with MPhi from aged mice was significantly lower than that seen with young MPhi. Consequently, this unresponsiveness can be overcome by a mixture of interleukin (IL)-1beta and IL-6. Upon stimulation with LPS, in comparison with young MPhi, aged MPhi secreted reduced amounts of IL-6, tumor necrosis factor alpha, IL-1beta, and IL-12, cytokines necessary for B cells to respond to TI Ag. LPS also induced aged MPhi to produce an excess of IL-10. Neutralization of IL-10 enhanced the production of proinflamatory cytokines by MPhi upon LPS stimulation and also induced Ab production by aged splenocytes. Thus, the inability of aged MPhi to help the B cell response appears to be caused by an excess of IL-10. As aged MPhi have a reduced number of cells expressing Toll-like receptor 4 and CD14, the imbalance in cytokine production might be partly a result of fewer cells expressing key components of the LPS receptor complex.

Androstenediol-induced restoration of responsiveness to influenza vaccination in mice

Androstenediol (AED), a metabolite of dehydroepiandrosterone (DHEA) regulates innate and adaptive immune responses. To examine whether AED could effectively reverse the age-associated decline of antiviral immunity, 3-, 10-, and 22-month-old mice were treated with AED-sulfate (AED-S) for 45 days beginning 10 days prior to vaccination. Subsequently, mice were primed and boosted with suboptimal doses of a commercially-available trivalent influenza vaccine. Treatment of 10-month-old animals with AED-S during vaccination increased the titer of circulating antiviral immunoglobulin G to levels comparable with those in 3-month-old mice. Furthermore, AED-S treatment protected 10-month-old animals from intranasal challenge with a lethal dose of influenza virus 21 days after secondary vaccination. Although AED-S treatment of 22-month-old mice did not enhance vaccine responses and failed to protect against lethal challenge, the data from the 10-month-old animals suggest that treatment with AED-S will prevent the early manifestations of immunosenescence.

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.

The effects of androstenediol and dehydroepiandrosterone on the course and cytokine profile of tuberculosis in BALB/c mice

Immunity to Mycobacterium tuberculosis requires a T helper 1 (Th1) cytokine balance accompanied by tumour necrosis factor-alpha (TNF-alpha), and activated macrophages. These facets of the immune response are sensitive to suppression by glucocorticoids (GC), which can reactivate and exacerbate tuberculosis in man and animals. Dehydroepiandrosterone (DHEA) and its derivative, 3beta,17beta androstenediol (AED), are reported to have antiglucocorticoid properties in vivo. We therefore investigated the effects of predetermined optimal doses of these compounds, on the course of pulmonary tuberculosis in an established model in BALB/c mice in which an early phase of Th1-mediated response accompanied by adrenal hyperplasia, is followed by a switch to Th2, progressive loss of TNF-alpha expression and disease progression. Both compounds were protective, particularly AED which caused a fall in bacterial counts and prolonged survival. These effects correlated with the appearance within 3 days of cellular infiltrates rich in cells expressing interleukin-2 (IL-2), IL-1alpha and TNF-alpha, and with partial suppression of the switch to IL-4 producing cells that occurred in controls. AED also caused enhanced development of granulomas at 14 days, and persistence of granuloma formation to 120 days, with a corresponding suppression of areas affected by pneumonia. Much of the therapeutic effect of AED and DHEA was obtained by treating for only the first 3 weeks, which is the phase of adrenal hyperplasia. These results suggest that the ratio of GC to anti-GC steroids may play a role in the pathogenesis of tuberculosis, and further investigation could lead to novel treatment strategies.

Effect of dehydroepiandrosterone (DHEA) on intestinal mucosal immunity in young adult and aging rats

The present study assesses the effectiveness of oral DHEA on the intestinal mucosal immune response in aging rats. Young adult (6 months) and aging (21 months) female rats received powdered rat chow with or without 0.2% DHEA for 23 days. The animals were immunized intraduodenally with either cholera toxin (CTx) or vehicle alone and boosted two weeks later. Seven days after boosting, serum, bile, small intestinal tissue, and liver were collected for analysis. Anti-CTx IgA antibody titers were measured in serum and bile and the concentration of anti-CTx antibody containing cells (ACCs) in the small intestinal lamina propria and liver were determined by quantitative immunohistochemistry. Intergroup comparisons indicated that there was only one significant difference in serum and none in bile anti-CTx IgA titers between CTx-immunized animals fed DHEA or the diet alone. Immunohistochemical analysis determined that the density and distribution patterns of ACCs within the lamina propria were unaffected by DHEA. Both DHEA-treated and control young immunized animals exhibited similar numbers of ACCs. Only 40% of the aging rats responded to intraduodenal immunization with CTx, as determined by the presence of ACCs in the intestine, regardless of the presence or absence of DHEA in the diet. These data suggest that DHEA in the diet does not enhance the intestinal mucosal immune response to intraduodenal CTx in either young adult or aging rats.

Dehydroepiandrosterone Supplements: Bringing Sense to Sensational Claims

OBJECTIVE

To summarize the current information about dehydroepiandrosterone (DHEA), a steroid hormone produced in the adrenal cortex.

METHODS

The biochemical and physiologic features of DHEA and its purported effects on overall age-related decline and on various disorders are reviewed. In addition, the potential side effects from administration of DHEA are discussed.

RESULTS

During the normal life cycle, levels of DHEA fluctuate, beginning with production of large quantities in the fetus, stopping at birth, resuming during ages 5 to 7 years, and increasing throughout puberty to maximal production in the 20s. Thereafter, DHEA levels progressively decline. This age-related decline in physiologic levels of DHEA has prompted speculation about a relationship between relative "DHEA deficiency" in older age and diseases of aging as well as the possibility of deriving benefits from administration of DHEA. Certain studies in animals (primarily rodents) have suggested anticancer effects of DHEA in pharmacologic doses and improvement in metabolism. In various studies in animals and humans, discrepant results have been found in the assessment of the association between DHEA levels and coronary artery disease. Likewise, the clinical significance of changes in immune function with DHEA treatment is unknown. Because DHEA is classified as a "nutritional supplement," it is not subjected to government regulation, and a potential exists for inaccurate dosage and impurities.

CONCLUSION

Studies have shown that DHEA influences multiple systems and disease processes in animals and humans; some of these effects could be considered beneficial and others detrimental. To date, no long-term health benefits from DHEA in "replacement" doses have been demonstrated.

Activation of human monocytes by LPS and DHEA

Dehydroepiandrosterone (DHEA) alone, whatever the concentration used, or lipopolysaccharide (LPS) alone at 0.2 ng/ml did not induce the release of interleukin-6 (IL-6) or tumor necrosis factor (TNF) by human monocytes. However DHEA (10[-9] M or 10[-12] M) in association with LPS (0.2 ng/ml) did induce the release of IL-6 and TNF. When human monocytes were activated by 1 microg/ml LPS, both IL-6 and TNF secretions were observed. Monocytes activated by both DHEA (10[-9] M or 1O[-12] M) and LPS (1 microg/ml) secreted IL-6 and TNF at a higher level than that observed for monocytes activated only by LPS (1 microg/ml) alone. DHEA alone, whatever the concentration used, or LPS alone at 0.2 ng/ml did not induce the activation of mitogen-activated protein kinases (MAPkinases) and protein kinase C (PKC) or the expression of c-fos and c-jun. However DHEA (10[-9] M or 10[-12] M) and 0.2 ng/ml LPS together induced the activation of both MAPKinases and PKC and the expression of c-fos and c-jun. Furthermore, the activation of PKC and MAPKinases and the expression of c-fos and c-jun were much greater when human monocytes were activated by both LPS (1 microg/ml) and DHEA (10[-9] M or 10[-12] M) than when the monocytes were activated only by LPS at 1 microg/ml. Therefore, DHEA and LPS displayed a synergistic effect on monocyte activation.

Use of licensed vaccines for active immunization of the immunocompromised host

The latter part of the 20th century has witnessed an unprecedented rise in the number of individuals with impaired immunity. This is primarily attributable to the increased development and use of antineoplastic therapy for malignancies, organ and bone marrow transplantation, and the AIDS epidemic. Individuals with impaired immunity are often at increased risk for infections, and they can experience more severe and complicated courses of infection. The lack of therapy for a variety of viruses and the rise in antimicrobial resistance of many pathogens have focused attention on vaccination to prevent infectious diseases. The efficacy of most licensed vaccines has been established in immunocompetent hosts. However, there is also considerable experience with most vaccines in those with impaired immunity. We reviewed the use of licensed live, inactivated, and polysaccharide vaccines in this group, and several themes emerged: (i) most vaccines are less immunogenic in those with impaired immunity than in normal individuals; (ii) live vaccines are generally contraindicated in this group; and (iii) the efficacy of many commonly used vaccines has not been established in people with impaired immunity. This review suggests that for most vaccines there are little or no efficacy data in those with impaired immunity but their use in this patient group is generally safe.

The effect of aging on IgD receptor expression by T cells and its functional implications

Exposure to oligomeric or aggregated (a), but not to monomeric (m), IgD causes a rapid (within 1 h) upregulation of IgD-R expression on CD4+ T cells from young, but not from aged, mice and on both CD4+ and CD8+ T cells from all young and from approximately 65% of aged humans. In normal young (but not in IgD-/-) mice, this increase in IgD-R expression is associated with a marked increase in primary and secondary antibody responses, transferable to both aged and young mice with T cells from aIgD pretreated donors. In both species, immunization causes a rise in the IgD-R+ expression in vivo in the young. In mice, mIgD abolishes both the induction of IgD-R expression and augmentation of immune responses, suggesting that interaction between IgD-R+ T and IgD+ B cells is needed. In aged humans, the ability of peripheral blood lymphocytes to exhibit IgD-R expression in response to aIgD in vitro or to influenza vaccine in vivo is strongly correlated to the individual's ability to produce antibody. In T cells from aged mice, but not from aged IgD-non-responder humans, IgD-R are able to come to the cell surface if an additional signal has been supplied, such as by (ionomycin/thapsigargin + aIgD). Agents which induce IgD-R and augmentation of antibody production in aged and young mice include phosphatidylcholine and dehydroepiandrosterone sulfate. The immunoaugmenting effect of pretreatment with these agents appears indeed due to IgD-R+ T cells, because it is abolished by mIgD.

Gulf War syndrome: is it due to a systemic shift in cytokine balance towards a Th2 profile?

The symptoms of Gulf War syndrome are compatible with the hypothesis that the immune system of affected individuals is biased towards a Th2-cytokine pattern. Factors that could lead to a Th2 shift among Gulf War veterans include exposure to multiple Th2-inducing vaccinations under stressful circumstances and the way in which such vaccinations were administered, which would be expected to maximise Th2 immunogenicity. These factors may have led to a long-term systemic shift towards a Th2-cytokine balance and to mood changes related to the immunoendocrine state. Other vaccines that lead to similar long-term, non-specific shifts in cytokine balance are well-established. If our hypothesis is proven, treatment may be possible with regimens that induce a systemic Th1 bias.

Cellular basis of decreased immune responses to pneumococcal vaccines in aged mice

Previously, model systems were developed in our laboratory to study murine immune responses to the 23-valent pneumococcal polysaccharide vaccine Pnu-Imune, both in vivo and in vitro (M. Garg and B. Subbarao, Infect. Immun. 60:2329-2336, 1992; M. Garg, A. M. Kaplan, and S. Bondada, J. Immunol. 152: 1589-1596, 1994). Using these systems, we found that aged mice did not respond to the vaccine in vivo or in vitro. Cell separation studies showed that the unresponsiveness of the aged spleen cells to the vaccine was not due to an intrinsic B-cell defect or to T-cell-mediated immunosuppression but resulted from an accessory cell deficiency. Irradiated spleen cells from young mice enabled the old mouse spleen cells to respond to the vaccine. Interestingly, irradiated spleen cells from old mice also restored the vaccine responsiveness in old mice but were required in greater numbers than the young mouse spleen cells to induce similar levels of response. The accessory cell was an adherent cell that could be removed by passage through Sephadex G-10 and thus may be a macrophage. Accessory function could also be provided by the cytokine interleukin-1 (IL-1), IL-4, or IL-5 but not IL-2 or IL-6. Thus, one reason for the deficient immune response to pneumococcal vaccine in aged mice is a quantitative defect in adherent accessory cells.

Relationship between humoral immunoaugmenting properties of DHEAS and IgD-receptor expression in young and aged mice

IgD-receptors are associated with augmented antibody production in vivo and are induced on CD4+ T cells by aggregated IgD in young but not in aged mice. In the current study orally or intraperitoneally administered DHEAS was found to enhance antibody production, as measured in a plaque-forming cell assay, and also to cause an increased expression of IgD-R on T cells in both young and aged mice. IgD-R+ T cells are enumerated by rosette cell formation with IgD-coated SRBC. Since, as shown previously, the immunoaugmenting effect of IgD-R+ T cells is blocked by injection of monomeric IgD, the effect of monomeric IgD was also examined in DHEAS-pretreated mice. The inhibitory effect obtained with monomeric IgD in these studies indicates that upregulation of IgD-R by DHEAS plays an important role in the immunoenhancing effect of this hormone. In addition, no significant effect of DHEAS was obtained on contact hypersensitivity to DNCB or on proliferative responses of T cells from young or aged mice. Aged but not young mice showed increases in the numbers of Ia+ epidermal Langerhans cells after DHEAS treatment.

Steroids as regulators of the mammalian immune response

The mammalian immune system is multicellular in composition, and its proper function requires careful control over complex developmental pathways and many distinct types of effector responses. Numerous overlapping mechanisms of intercellular communication are needed to accomplish the tasks of proper regulation of the diverse cell types that constitute this essential protective system. One mechanism occurs by direct cell-to-cell contact through the interaction of membrane-associated molecules. Examples of this type of communication include the interaction that takes place between the antigen-specific T-cell receptor and the foreign peptides that are bound to major histocompatibility complex molecules, as well as costimulatory molecule interactions with their specific ligands expressed on antigen-presenting cells (e.g., CD28 and B7-1 or B7-2). A second mechanism occurs through the production, secretion, and activities of soluble mediators, collectively known as the cytokines. The cytokines are represented by a large and diverse group of molecules that are produced by a wide variety of cell types. Unique species of cytokines bind to specific membrane-associated receptors on target cells, inducing the activation of particular signal-transduction pathways. These processes subsequently lead to the diversity of cytokine-linked changes in cellular physiology. Some of the cytokines exert their influences in vivo via endocrine routes, although it is far more common for intercellular communication via cytokines to occur microenvironmentally via paracrine or autocrine pathways. The object of this review is to provide evidence supporting the concept that one mechanism for upstream regulation of cytokine production by immunocompetent cell types is controlled by the regulatory activities of various steroid hormones. Strain variation in susceptibility to infectious agents, the condition of immunosenescence, and the processes that control the development of common mucosal immunity are used as examples of immune mechanisms that may be under steroid hormone control.

The development of effective vaccine adjuvants employing natural regulators of T-cell lymphokine production in vivo

Steroid hormones are important regulators of gene function in vivo. A number of naturally occurring species of steroid hormones are able to qualitatively and quantitatively influence the production of lymphokines by activated T cells in vitro. Similar mechanisms are probably also occurring naturally in vivo and could explain why mucosal and nonmucosal lymphoid organs harbor T cells having unique potentials for lymphokine production. It was established that the topical application of 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) to normal mice changed the pattern of lymphokines produced by activated T cells isolated from the draining peripheral lymph nodes. The hormone-treated T cells produced a pattern of lymphokines similar to that normally found in Peyer's patches. Subcutaneous vaccination with a protein antigen, in a site afferent to 1,25(OH)2D3-manipulated lymph nodes, resulted in an enhanced serum antibody response and was uniquely capable of also stimulating a common mucosal immune response to the antigen as well. Common mucosal immunity was confirmed by demonstrating the presence of antigen-specific IgA and IgG responses in a number of mucosal secretions and by further establishing that antibody-secreting plasma cells had migrated to the lungs and small intestines of the hormone-treated and vaccinated animals. Additional experiments established that common mucosal immunity could also be induced in aged animals as long as the immune system of the vaccinated animals was functioning normally. This was accomplished by providing the aged animals with a dietary supplement of dehydroepiandrosterone sulfate (DHEAS). Previous studies by us have documented that aged animals provided with replacement levels of DHEAS, a natural steroid hormone whose endogenous production declines with advancing age, are able to mount normal systemic humoral and cellular immune response following subcutaneous vaccination with a variety of protein and polysaccharide antigens. The combination of supplemental DHEAS therapy with topical 1,25(OH)2D3 treatment at the time of vaccination provided the conditions needed to generate mucosal and systemic immune responses to inactivated influenza virus antigen by old animals.