The role of endogenous steroid hormones in the generation of T helper 2-mediated autoimmunity in mercuric chloride-treated Brown-Norway rats

Impact of DHEA(S) and cortisol on immune function in aging: a brief review

A decline in the human immune system that occurs with aging is known as immunosenescence. Several factors are involved in the process, including reduced neutrophil function and cytotoxic capacity of natural killer (NK) cells, thymus atrophy and reduced naïve T cell number, and lowered B cell antibody production in response to antigen. The endocrine system, specifically the hypothalamus–pituitary–adrenal axis, plays an important role in modulating immune function. With aging an imbalance occurs between two adrenal hormones, cortisol and DHEA, that have opposing actions on immune function. This brief review explores the interactions between cortisol and DHEA and their effects on immune function in aging, as well as potential methods to combat the endocrine-related contribution to immunosenescence, including DHEA supplementation and exercise.

Predictors and markers of resistance to neurotropic nematode infection in rodent host

Parasite-mediated selection is currently believed to play an important role in life-history evolution. To assess how simple hematoserological and biochemical condition indices reflect host immunocompetence and infection resistance controlled laboratory experiments are required. We addressed these issues by infecting laboratory rats with the standard dose of embryonated eggs of a neurotropic nematode Toxocara canis. Urine baseline corticosterone concentrations, measured 1 week before infection, predicted the number of nematode larvae later recovered from host brains. Thus, this noninvasive clinical marker appeared useful for assessment of potential infection resistance. Rats who had accumulated high number of larvae in their brains and muscle had large spleens and high peripheral eosinophil counts 17 days postinfection. This finding is consistent with the concept that induction of eosinophilic Th2 type humoral immune response benefits the parasite rather than host. Hence, excessive peripheral eosinophilia and spleen enlargement are not markers of efficient antiparasite response in larval toxocariasis.

Severity of murine collagen-induced arthritis correlates with increased CYP7B activity: enhancement of dehydroepiandrosterone metabolism by interleukin-1beta

OBJECTIVE

The endogenous steroid dehydroepiandrosterone (DHEA) has been reported to play a role in rheumatoid arthritis (RA). DHEA is metabolized by the P450 enzyme CYP7B into 7alpha-OH-DHEA, which has immunostimulating properties. This study was undertaken to investigate the putative role of CYP7B in arthritis using murine collagen-induced arthritis (CIA), an interleukin-1beta (IL-1beta)-dependent model.

METHODS

DBA/1J mice were immunized and administered a booster with type II collagen. The presence of 7alpha-OH-DHEA was determined in both arthritic and nonarthritic joints and the serum of CIA mice by radioimmunoassay. CYP7B messenger RNA (mRNA) expression was analyzed in synovial biopsy samples, and in fibroblast-like synoviocytes (FLS) isolated from these synovial biopsy samples, by reverse transcriptase-polymerase chain reaction (RT-PCR). In addition, the regulatory role of IL-1beta on CYP7B activity in FLS was determined using RT-PCR, Western blotting, and high-performance liquid chromatography.

RESULTS

In knee joint synovial biopsy samples from arthritic mice, 7alpha-OH-DHEA levels were 5-fold higher than in nonarthritic mice. Elevated levels of 7alpha-OH-DHEA were accompanied by an increase in CYP7B mRNA expression and were positively correlated with disease severity. In serum, no differences in 7alpha-OH-DHEA levels were observed between arthritic and nonarthritic mice. Incubation of FLS with IL-1beta resulted in a dose-dependent increase in 7alpha-OH-DHEA formation. In addition, IL-1beta enhanced CYP7B mRNA and CYP7B protein levels in FLS.

CONCLUSION

Disease progression in CIA is correlated with enhanced CYP7B activity, which leads to locally enhanced 7alpha-OH-DHEA levels. Elevated IL-1beta levels within the arthritic joint may regulate this increase in CYP7B activity.

Stress and the immune system

Stressors can positively or adversely affect immune and inflammatory responses. However, the current understanding of these effects at the cellular and molecular levels is not sufficient to allow prediction of the effects of a particular stressor on a particular immune or inflammatory function. Three complementary conceptual frameworks are presented that may prove useful in developing such an understanding. In addition, specific examples of the action of particular stress mediators on particular immune or inflammatory end points are discussed, and the relationship of these observations to the conceptual frameworks is indicated. Several of the effects discussed are relevant clinically, and the prospects for pharmacological intervention to prevent adverse effects of stressors on the immune system are discussed. Finally, some of the factors that can (sometimes unexpectedly) influence the outcome of stress-immunology studies and some of the pitfalls that continue to make this area of research controversial in some circles are discussed.

Does cortisol bias cytokine production in cultured porcine splenocytes to a Th2 phenotype?

Glucocorticoids are reported to bias the production of cytokines from a type 1 to a type 2 phenotype. However, this dogma has been advanced largely from studies utilizing potent glucocorticoid analogs, particularly dexamethasone (DEX). Although studies utilizing DEX certainly have clinical and pharmacological relevance, DEX is probably not the best glucocorticoid for studies designed to evaluate the interaction and regulation of endogenous corticosteroids with immune cells in vivo in the domestic pig. Functional measures of immune suppression suggest that the pig is relatively resistant to DEX. Furthermore, type II corticosteroid receptors exclusively bind DEX with high affinity, whereas type I receptors, the so-called mineralocorticoid receptors, have a higher affinity for cortisol. In addition, DEX is not bound by serum binding proteins as are endogenous corticosteroids. These issues prompted us to revisit glucocorticoid regulation of type 1 and type 2 cytokines in cultured pig splenocytes and to test the broad hypothesis that cortisol biases cytokine production in favor of a Th2 response. We evaluated interferon gamma (IFNgamma) (also interleukin 2 (IL-2) in one experiment) and interleukin 10 (IL-10) as representative Th1 and Th2 cytokines, respectively. Furthermore, we evaluated macrophage migration inhibitory factor (MIF) because it is reported to be an essential factor in T cell activation; it is also upregulated by glucocorticoids and reported to be a product of Th2 lymphocytes. In general, both IFNgamma and IL-10 were sensitive to cortisol inhibition early in culture. However, IFNgamma ultimately escaped cortisol inhibition, whereas IL-10 continued to be substantially suppressed by high physiological concentrations of cortisol. Similarly, MIF mRNA could be suppressed by cortisol, but only when cortisol was added to cultures after ConA (concanavalin A) stimulation of splenocytes. So, taken together, our studies do not support the hypothesis that cortisol favors a Th2 cytokine profile in cultured pig splenocytes.

A synthetic androstene derivative and a natural androstene metabolite inhibit relapsing-remitting EAE

Experimental allergic encephalomyelitis (EAE), a Th1 polarized demyelinating disease of the central nervous system (CNS), shares many pathological and clinical similarities with multiple sclerosis (MS), and thus represents an attractive animal model for this disease. The goal of this study was to evaluate the suppressive effects of fluasterone (HE2500), a synthetic androstene derivative, and androstenetriol (HE2200), a natural androstene hormone on EAE. SJL mice were immunized with proteolipid protein (PLP) 139-151 peptide/CFA to induce EAE. Starting on day -7, animals were given daily injections (s.c.) of derivatives (3.0 mg) in vehicle, or vehicle alone for 33 days. Both HE2500 and HE2200 significantly delayed the onset, reduced the peak clinical score and cumulative disease index of EAE, and prevented or significantly attenuated relapses. Lower doses or other routes of administration were less effective. Moreover, T cells from treated mice had significantly reduced PLP 139-151-specific T cell proliferation responses and reduced numbers of TNF-alpha- and IFN-gamma-producing cells in the CNS. Daily treatment of B10.PL mice with HE2500, starting on day 0, completely prevented the development of disease in these animals. Finally, SJL mice treated with HE2500 at EAE onset showed significantly reduced mean clinical scores. Thus, these compounds, which have been reported to have a few androgenic or estrogenic side effects, appear to have a potent inhibitory activity in EAE. These observations suggest that HE2500 and/or HE2200 limit the production of autoimmune Th1 associated cytokines, and ultimately may be beneficial for patients with MS or other autoimmune diseases.

Quantitative aspects of stress-induced immunomodulation

Recent studies indicate that neuroendocrine-immune interactions can cause sufficient immunosuppression to adversely affect human health, but quantitative relationships between stress-related hormones or neurotransmitters and immune function have not been well documented. The mechanisms of stress-induced immunomodulation cannot be fully understood solely by identifying the hormones, neurotransmitters, and cytokines involved. Quantitative relationships and interactions must also be understood. Depending on the nature and duration of the stressor and the immunological parameter under investigation, stress responses can enhance, have no effect, or suppress immunological parameters. These quantitative relationships have implications with regard to safety assessment of drugs and chemicals and with regard to potential development of pharmacological interventions to ameliorate some of the immunosuppressive effects of stress. This review describes selected studies that relate the quantity and duration of exposure to stress-related neuroendocrine mediators to modulation of the immune system. These studies provide a useful starting point, but they also illustrate how much work remains to achieve a fully integrated qualitative and quantitative understanding of stress-induced immunomodulation.