Synergistic interaction of catecholamine hormones and Mycobacterium avium results in the induction of interleukin-10 mRNA expression by murine peritoneal macrophages

The complex interplay between stress and bacterial infections in animals

Over the past decade, an increasing awareness has arisen of the role of neuroendocrine hormones in the susceptibility of mammalian hosts to a bacterial infection. During a stress response, glucocorticoids, catecholamines and neuroendocrine factors are released into the circulation of the host. For a long time the effects of stress on the course of an infection have been exclusively ascribed to the direct effect of stress-related hormones on the immune system and the intestinal barrier function. Chronic stress is known to cause a shift from T helper 1-mediated cellular immunity toward T helper 2-mediated humoral immunity, which can influence the course of an infection and/or the susceptibility to a microorganism. Bacteria can however also respond directly to stress-related host signals. Catecholamines can alter growth, motility, biofilm formation and/or virulence of pathogens and commensal bacteria, and as a consequence influence the outcome of infections by these bacteria in many hosts. For some bacteria, such as Salmonella, Escherichia coli and Pseudomonas aeruginosa it was shown that this influence is regulated by quorum sensing mechanisms. In this manuscript an overview of how and when stress influences the outcome of bacterial infections in animals is provided.

Glucocorticoids produced during exercise may be necessary for optimal virus-induced IL-2 and cell proliferation whereas both catecholamines and glucocorticoids may be required for adequate immune defense to viral infection

Prolonged, exhaustive exercise has been associated with impaired immune responsiveness and increased susceptibility to infection. We have shown that one bout of exercise to fatigue followed by viral challenge increases mortality. Stress hormones such as corticosteroids and catecholamines have been suggested as potential mediators of exhaustive exercise-induced immunosuppression. The purpose of this study was to determine whether the administration of pharmacological agents to block the effect of catecholamines or corticosteroids would minimize the immunosuppression associated with this type of exercise. Mice either exercised to fatigue or were exposed to control conditions, and mice received an i.p. injection of either nadolol (beta-adrenergic receptor antagonist), RU486 (glucocorticoid type II receptor antagonist), or vehicle. Fifteen minutes post-exercise, mice were exposed to viral infection (Herpes simplex virus; HSV) via an intranasal route, and cells were collected 3 days post-infection. The results showed that exercise suppressed HSV-specific cell proliferation, HSV-specific IL-2, and IFN-gamma, but did not alter these same immune parameters when the mitogen ConA was used to stimulate cells. In addition, exercise reduced NK cell cytotoxicity, alveolar cell TNFalpha, and peritoneal IL-1beta, but did not affect IL-10. The pharmacological blockade did not attenuate the exercise-associated immunosuppression. In fact, RU486 treatment exacerbated the exercise-induced decline in HSV-induced IL-2 production and cell proliferation. RU486 and nadolol treatment also tended to decrease IL-10, IFN-gamma, TNFalpha (nadolol only), and IL-1beta (RU486 only) in both exercise and control mice, suggesting that stress hormones may be necessary during infection for optimal responsiveness. These findings suggest that suppression of immune defenses during viral infection persists for at least 3 days post-exercise, and stress hormones may be essential for optimal immune defense to viral challenge, rather than detrimental.

Regulation of nitric oxide production from macrophages by lipopolysaccharide and catecholamines

Catecholamines are elaborated in stress responses to mediate vasoconstriction, and elevate systemic vascular resistance and blood pressure. They are elaborated in disorders such as sepsis, cocaine abuse, and cardiovascular disease. The aim of the study was to determine whether catecholamines affect nitric oxide (NO) production, as NO is a vasodilator and counteracts the harmful effects of catecholamines. RAW264.7 macrophage cells were cultured with lipopolysaccharide (LPS)+/-epinephrine, norepinephrine, and dopamine at 5x10(-6)M concentrations for 24h. Supernatants were harvested for measuring NO by spectrophotometry using the Greiss reagent and cells were harvested for detecting inducible NO synthase (iNOS) by Western blot. NO production in RAW 264.7 macrophages was increased significantly by addition of LPS (0.5-10ng/ml) in a dose-dependent fashion. The NO production induced by LPS was further enhanced by epinephrine and norepinephrine, and to a lesser extent by dopamine. These increases in NO correlated with expression of iNOS protein in these cells. The enhancing effect of iNOS synthesis by epinephrine and norepinephrine on LPS-induced macrophages was down regulated by beta-adrenoceptor antagonist, propranolol, and dexamethasone. The results suggest that catecholamines have a synergic effect on LPS in induction of iNOS synthesis and NO production, and this may mediate some of the vascular effects of infection. These data support a novel role for catecholamines in disorders such as septic shock and cocaine use, and indicate that beta-adrenoceptor antagonists and glucocorticoids may be used therapeutically for modulation of the catecholamine-NO axis in disease states.

Resistance of macrophages to Mycobacterium avium is induced by alpha2-adrenergic stimulation

The ability of macrophages to control the growth of microorganisms is increased by macrophage activation. Previously, it was shown that epinephrine activated mouse macrophages to resist the growth of Mycobacterium avium via alpha(2)-adrenergic stimulation. In the present study, we show that the alpha(2)-adrenergic agonist (alpha(2)-agonist) clonidine induced resistance to M. avium growth in the RAW264.7 mouse macrophage cell line. The ability of catecholamines to induce resistance to mycobacteria was specific to alpha(2)-adrenergic stimulation, as alpha(1)-, beta(1)-, and beta(2)-agonists had no effect. Receptor signaling through Gi proteins was required. A G-protein antagonist specific for the alpha subunits of the Go/Gi family blocked the increased resistance induced by clonidine, while a Gs-protein antagonist was without effect. Both nitric oxide (NO) production and superoxide (O(2)(-)) production were required for the increased resistance to M. avium growth induced by clonidine. Although NO production was required, clonidine did not increase the level of NO in M. avium-infected cells. Since NO and O(2)(-) interact to produce peroxynitrite (ONOO(-)), we examined whether ONOO(-) mediates the increased resistance to M. avium induced by clonidine. 5,10,15,20-Tetrakis(4-sulfonatophenyl)prophyrinato iron (III) chloride (FeTPPS), a specific scavenger of ONOO(-), inhibited the effect of clonidine on M. avium growth. Clonidine also increased the production of ONOO(-) in M. avium-infected RAW264.7 cells, as measured by the oxidation of 123-dihydrorhodamine and the production of nitrated tyrosine residues. We therefore conclude that alpha(2)-adrenergic stimulation activates macrophages to resist the growth of M. avium by enhancing the production of ONOO(-).

NFkappaB and Sp1 elements are necessary for maximal transcription of toll-like receptor 2 induced by Mycobacterium avium

We have previously reported that Toll-like receptor (TLR) 2 mRNA was induced after infection with Mycobacterium avium. To investigate the molecular basis of TLR2 expression in macrophages, we cloned and analyzed the murine putative 5'-proximal promoter. Transient transfection of a 326-bp region from nucleotides -294-+32 relative to the first transcription start site was sufficient to induce maximal luciferase activity at the basal level and after infection with M. avium in J774A.1 cells. Sequence analysis showed that the region lacked a TATA box but contained two typical stimulating factor (Sp) 1 sites, two NF-kappaB sites, one IFN-regulatory factor site and one AP-1 site. Site-directed mutagenesis revealed that the NF-kappaB and Sp1 sites but not the IFN-regulatory factor site or the AP-1 site contributed to the basal level and the induction of luciferase activity during M. avium infection. Binding of Sp1/Sp3 and NF-kappaB (p50/p65) was confirmed by EMSA. Further studies showed that three copies of Sp1 elements or NF-kappaB elements are not sufficient to confer M. avium induction on a heterologous promoter. By contrast, overexpression of NF-kappaB p65 caused a strong increase in transcription from an intact TLR2 promoter, whereas it caused only a partial increase in promoter activity when cotransfected with the TLR2 promoter with one of the Sp1 sites mutated. Sp1 and NF-kappaB were the minimum mammalian transcription factors required for effective TLR2 transcriptional activity when transfected into Drosophila Schneider cells. Together, these data provide genetic and biochemical evidence for NF-kappaB as well as Sp1 in regulating TLR2 transcription.

Regulation of toll-like receptor 2 expression by macrophages following Mycobacterium avium infection

Recent studies have implicated Toll-like receptors (TLR), especially TLR2 and TLR4, as sentinel receptors that signal the interaction of macrophages with bacterial pathogens via a NF-kappaB-mediated pathway. The regulation of TLR gene expression, however, has not been intensively studied. Here, we report that TLR2 mRNA was induced following infection of murine macrophages with Mycobacterium avium. The changes in TLR2 mRNA correlated with an increase in TLR2 surface expression. Infection with M. avium resulted in a concomitant decrease in TLR4 mRNA. The effect of M. avium infection on TLR2 mRNA appeared to be mediated, in part, by TLR2 because the induction of the mRNA was partially blocked by preincubation of the macrophages with an anti-human TLR2 Ab. In contrast, the effect of LPS stimulation was mediated via TLR4 because infection of macrophages from LPS(d) mice, which do not express active TLR4, resulted in an increase in TLR2 mRNA, while treatment of macrophages from these mice with LPS failed to induce TLR2 mRNA. Several cytokines, including TNF-alpha, IL-1alpha, and GM-CSF, but not IFN-gamma, induced TLR2 mRNA. M. avium infection resulted in the induction of TLR2 mRNA by macrophages from both TNFRI knockout and NF-kappaB p50 knockout mice.