Estradiol protects female rats against sepsis induced by Enterococcus faecalis improving leukocyte bactericidal activity

Preeclamptic programming unevenly perturbs inflammatory and renal vasodilatory outcomes of endotoxemia in rat offspring: modulation by losartan and pioglitazone

Introduction: Preeclampsia (PE) enhances the vulnerability of adult offspring to serious illnesses. The current study investigated whether preeclamptic fetal programming impacts hemodynamic and renal vasodilatory disturbances in endotoxic adult offspring and whether these interactions are influenced by antenatal therapy with pioglitazone and/or losartan. Methods: PE was induced by oral administration of L-NAME (50 mg/kg/day) for the last 7 days of pregnancy. Adult offspring was treated with lipopolysaccharides (LPS, 5 mg/kg) followed 4-h later by hemodynamic and renovascular studies. Results: Tail-cuff measurements showed that LPS decreased systolic blood pressure (SBP) in male, but not female, offspring of PE dams. Moreover, PE or LPS reduced vasodilations elicited by acetylcholine (ACh, 0.01-7.29 nmol) or N-ethylcarboxamidoadenosine (NECA, 1.6-100 nmol) in perfused kidneys of male rats only. The latter effects disappeared in LPS/PE preparations, suggesting a postconditioning action for LPS against renal manifestation of PE. Likewise, elevations caused by LPS in serum creatinine and inflammatory cytokines (TNFα and IL-1β) as well as in renal protein expression of monocyte chemoattractant protein-1 (MCP-1) and AT1 receptors were attenuated by the dual PE/LPS challenge. Gestational pioglitazone or losartan reversed the attenuated ACh/NECA vasodilations in male rats but failed to modify LPS hypotension or inflammation. The combined gestational pioglitazone/losartan therapy improved ACh/NECA vasodilations and eliminated the rises in serum IL-1β and renal MCP-1 and AT1 receptor expressions. Conclusion: Preeclamptic fetal programming of endotoxic hemodynamic and renal manifestations in adult offspring depends on animal sex and specific biological activity and are reprogrammed by antenatal pioglitazone/losartan therapy.

The Pathological Activation of Microglia Is Modulated by Sexually Dimorphic Pathways

Microglia are the primary immunocompetent cells of the central nervous system (CNS). Their ability to survey, assess and respond to perturbations in their local environment is critical in their role of maintaining CNS homeostasis in health and disease. Microglia also have the capability of functioning in a heterogeneous manner depending on the nature of their local cues, as they can become activated on a spectrum from pro-inflammatory neurotoxic responses to anti-inflammatory protective responses. This review seeks to define the developmental and environmental cues that support microglial polarization towards these phenotypes, as well as discuss sexually dimorphic factors that can influence this process. Further, we describe a variety of CNS disorders including autoimmune disease, infection, and cancer that demonstrate disparities in disease severity or diagnosis rates between males and females, and posit that microglial sexual dimorphism underlies these differences. Understanding the mechanism behind differential CNS disease outcomes between men and women is crucial in the development of more effective targeted therapies.

Environmental microplastics exposure decreases antioxidant ability, perturbs gut microbial homeostasis and metabolism in chicken

The widespread presence and accumulation of microplastics (MPs) in organisms has led to their recognition as a major global ecological issue. There is a lot of data on how MPs affect the physiology and behavior of aquatic species, but the effects of MPs on poultry are less understood. Therefore, we aimed to explore the adverse effects and mechanisms of MPs exposure to chicken health. Results indicated that MPs exposure decreased growth performance and antioxidant ability and impaired chickens' intestine, liver, kidney, and spleen. Additionally, the gut microbiota in chickens exposed to MPs showed a significant decrease in alpha diversity, accompanied by significant alternations in taxonomic compositions. Microbial taxonomic investigation indicated that exposure to MPs resulted in a significant increase in the relative proportions of 11 genera and a distinct decline in the relative percentages of 3 phyla and 52 genera. Among decreased bacterial taxa, 11 genera even couldn't be detected in the gut microbiota of chickens exposed to MPs. Metabolomics analysis indicated that 2561 (1190 up-regulated, 1371 down-regulated) differential metabolites were identified, mainly involved in 5 metabolic pathways, including D-amino acid metabolism, ABC transporters, vitamin digestion and absorption, mineral absorption, and histidine metabolism. Taken together, this study indicated that MPs exposure resulted in adverse health outcomes for chickens by disturbing gut microbial homeostasis and intestinal metabolism. This study also provided motivation for environmental agencies worldwide to regulate the application and disposal of plastic products and decrease environmental contamination.

Polydatin Improves Sepsis-Associated Encephalopathy by Activating Sirt1 and Reducing p38 Phosphorylation

INTRODUCTION

Our previous study confirmed that polydatin (PD) can alleviate sepsis-induced multiorgan dysfunction (in the vascular endothelium, kidney, and small intestine) by activating Sirt1 and that PD protects against traumatic brain injury in rats via increased Sirt1 and inhibition of the p38-mediated mitogen-activated protein kinase (MAPK) pathway. We aim to investigate whether PD may also attenuate sepsis-associated encephalopathy (SAE).

METHODS

In this study, we constructed an SAE mouse model by cecal ligation and puncture (CLP) and measured Sirt1 protein activity, p38 phosphorylation, brain tissue pathological damage, pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6), mitochondrial function (mitochondrial membrane potential, ATP content, and reactive oxygen species), neurological function, and animal survival time. Sirt1 selective inhibitor Ex527 and p38 inhibitor SB203580 were used to explore the possible mechanism of PD in SAE.

RESULTS

We confirmed that PD inhibits neuroinflammation evidenced by reduced proinflammatory cytokines. In addition, PD protects mitochondria as demonstrated by restored mitochondrial membrane potential and adenosine triphosphate (ATP) content, and decreased reactive oxygen species (ROS) level. As we expected, p38 inhibition reduces neuroinflammation and mitochondrial damage. In contrast, Sirt1 inhibition aggravates cerebral cortex mitochondrial damage and neuroinflammation and promotes phosphorylation of p38. Mechanistically, PD treatment suppressed p38 phosphorylation and consequently reduced the neuroinflammatory response, and these effects were blocked by the Sirt selective inhibitor Ex527.

CONCLUSIONS

This study, to the best of our knowledge, is the first to demonstrate that PD alleviates SAE, at least partially, by upregulating Sir1-mediated neuroinflammation inhibition and mitochondrial function protection.

Impact of Sex Hormones on Macrophage Responses to Coxiella burnetii

Introduction

Q fever, a zoonosis caused by Coxiella burnetii, affects more males than females despite a similar level of exposure. A protective role of estradiol has been reported in mice, suggesting that sex hormones are involved in C. burnetii infection. We wondered whether the responses of monocytes and monocyte-derived macrophages (MDMs) to C. burnetii are influenced by sex hormones.

Materials and Methods

The bacterial intracellular fate in monocytes was studied using quantitative PCR, and monocyte cytokine production in response to C. burnetii was assessed using qRT-PCR and immunoassays. Before infection, MDMs from males and females were incubated with testosterone and estradiol, respectively.

Results

Bacterial uptake and persistence were similar in monocytes from males and females but were slightly increased in male MDMs. The expression of inflammatory genes, including those encoding TNF and CXCL10, was higher in MDMs from females than in MDMs from males infected by C. burnetii. Adding testosterone to male MDMs amplified their immunoregulatory properties, including increased expression of IL10 and TGFB genes and TGF-β production in response to C. burnetii. In contrast, adding estradiol to MDMs from females had no effect on their inflammatory profile.

Conclusion

The stronger inflammatory profile of macrophages from females may have a protective role, likely under estrogen control, while testosterone may affect disease progression by promoting an anti-inflammatory response. This finding may have consequences for personalized management of patients with Q fever.

Sexual Dimorphism and Gender in Infectious Diseases

Epidemiological studies and clinical observations show evidence of sexual dimorphism in infectious diseases. Women are at less risk than men when it comes to developing most infectious diseases. However, understanding these observations requires a gender approach that takes into account an analysis of both biological and social factors. The host’s response to infection differs in males and females because sex differences have an impact on hormonal and chromosomal control of immunity. Estradiol appears to confer protective immunity, while progesterone and testosterone suppress anti-infectious responses. In addition, genetic factors, including those associated with sex chromosomes, also affect susceptibility to infections. Finally, differences in occupational activities, lifestyle, and comorbidities play major roles in exposure to pathogens and management of diseases. Hence, considering sexual dimorphism as a critical variable for infectious diseases should be one of the steps taken toward developing personalized therapeutic approaches.

Sepsis as a Pan-Endocrine Illness-Endocrine Disorders in Septic Patients

Sepsis is defined as "life-threatening organ dysfunction caused by a dysregulated host response to infection". One of the elements of dysregulated host response is an endocrine system disorder. Changes in its functioning in the course of sepsis affect almost all hormonal axes. In sepsis, a function disturbance of the hypothalamic-pituitary-adrenal axis has been described, in the range of which the most important seems to be hypercortisolemia in the acute phase. Imbalance in the hypothalamic-pituitary-thyroid axis is also described. The most typical manifestation is a triiodothyronine concentration decrease and reverse triiodothyronine concentration increase. In the somatotropic axis, a change in the secretion pattern of growth hormone and peripheral resistance to this hormone has been described. In the hypothalamic-pituitary-gonadal axis, the reduction in testosterone concentration in men and the stress-induced "hypothalamic amenorrhea" in women have been described. Catecholamine and β-adrenergic stimulation disorders have also been reported. Disorders in the endocrine system are part of the "dysregulated host response to infection". They may also affect other components of this dysregulated response, such as metabolism. Hormonal changes occurring in the course of sepsis require further research, not only in order to explore their potential significance in therapy, but also due to their promising prognostic value.

Risk factors for enterococcal urinary tract infections: a multinational, retrospective cohort study

Complicated urinary tract infection (cUTI) is a frequent cause of morbidity. In this multinational retrospective cohort study, we aimed to demonstrate risk factors for enterococcal UTI. Univariate and multivariate analyses of risk factors for enterococcal infection were performed. Among 791 hospitalized patients with cUTI, enterococci accounted for approximately 10% of cases (78/791). Risk factors for enterococcal UTI in multivariable analysis were male gender, age range of 55-75 years, catheter-associated UTI, and urinary retention. This information may assist treating physicians in their decision-making on prescribing empiric anti-enterococcus treatment to hospitalized patients presenting with cUTI and thus improve clinical outcomes.

Long-term aerobic exercise training-induced anti-inflammatory response and mechanisms: Focusing on the toll-like receptor 4 signaling pathway

Toll-like receptor 4 (TLR-4), which regulate inflammatory reactions, has become a popular research topic in recent years. This article reviews the latest scientific evidence on the regulation of TLR-4 by regular aerobic exercise training. The literature shows that long-term regular aerobic exercise training can effectively attenuate the expression of TLR-4 in immune cells and regulate its downstream intracellular cascade, including the p38 and PI3K/Akt signaling pathways. This further reduces cytokines secretion by inflammatory cells, which enhances immune system. We consider that the scientific evidence that long-term aerobic exercise training improves the inflammatory response provides a reasonable basis for using aerobic exercise training as a treatment for patients.

Endocrine disrupter chemicals affect the humoral antimicrobial activities of gilthead seabream males even upon the cease of the exposure

17α-ethynilestradiol (EE₂) and tamoxifen (Tmx) are pollutants world-wide distributed in aquatic environments. Gilthead seabream, Sparus aurata L., is highlighted as a species model of intensively culture in anthropogenic disturbed environments. The effects of these pollutants on gilthead seabream reproduction and some immune responses have been described but, the humoral innate antimicrobial activities have never received attention. In this work we analysed the latest in the plasma of gilthead seabream males of different ages and reproductive stages treated with 0, 2.5, 5 or 50 μg EE₂ or 100 μg Tmx g^-1 food during different times of exposure and of reverting to commercial diet (recovery). The peroxidase and protease activities decreased as the spermatogenesis of the first reproductive cycle (RC) proceeded in control fish. However, only protease and antiprotease activities showed different level at different stages of the second RC in control fish, but showed scarce disruption in fish treated with EE₂ or Tmx. Peroxidase and bactericide activities are more sensitive to EE₂, than to Tmx. The effects induced by EE₂ varied depending on the activity analyzed, the dose and the time of exposure and the reproductive stage and the age of the specimens.

Pre-eclamptic Fetal Programming Alters Neuroinflammatory and Cardiovascular Consequences of Endotoxemia in Sex-Specific Manners

Pre-eclampsia (PE)-induced fetal programming predisposes offspring to health hazards in adult life. Here, we tested the hypothesis that pre-eclamptic fetal programming elicits sexually dimorphic inflammatory and cardiovascular complications to endotoxemia in adult rat offspring. PE was induced by oral administration of L-NAME (50 mg/kg per day for seven consecutive days) starting from day 14 of conception. Cardiovascular studies were performed in conscious adult male and female offspring preinstrumented with femoral indwelling catheters. Compared with non-PE male counterparts, intravenous administration of lipopolysaccharide (LPS, 5 mg/kg) to PE male offspring caused significantly greater 1) falls in blood pressure, 2) increases in heart rate, 3) rises in arterial dP/dtmax, a correlate of left ventricular contractility, and 4) decreases in time- and frequency-domain indices of heart rate variability (HRV). By contrast, the hypotensive and tachycardic actions of LPS in female offspring were independent of the pre-eclamptic state and no clear changes in HRV or dP/dtmax were noted. Measurement of arterial baroreflex activity by vasoactive method revealed no sex specificity in baroreflex dysfunction induced by LPS. Immunohistochemical studies showed increased protein expression of toll-like receptor 4 in heart as well as in brainstem neuronal pools of the nucleus of solitary tract and rostral ventrolateral medulla in endotoxic PE male, but not female, offspring. Enhanced myocardial, but not neuronal, expression of monocyte chemoattractant protein-1 was also demonstrated in LPS-treated male offspring. Together, pre-eclamptic fetal programming aggravates endotoxic manifestations of hypotension and autonomic dysfunction in male offspring via exacerbating myocardial and neuromedullary inflammatory pathways. SIGNIFICANCE STATEMENT: Current molecular and neuroanatomical evidence highlights a key role for pre-eclamptic fetal programming in offspring predisposition to health hazards induced by endotoxemia in adult life. Pre-eclampsia accentuates endotoxic manifestations of hypotension, tachycardia, and cardiac autonomic dysfunction in male offspring via exacerbating myocardial and central inflammatory pathways. The absence of such detrimental effects in female littermates suggests sexual dimorphism in the interaction of pre-eclamptic fetal programming with endotoxemia.

Ovariectomy provokes inflammatory and cardiovascular effects of endotoxemia in rats: Dissimilar benefits of hormonal supplements

The female gender is protected against immunological complications of endotoxemia. Here we investigated whether gonadal hormone depletion by ovariectomy (OVX) uncovers inflammatory and cardiovascular effects of endotoxemia and whether these effects are reversed by hormone replacement therapies. Changes in inflammatory cytokines, blood pressure (BP), left ventricular (LV) function, and cardiac autonomic activity caused by lipopolysaccharide (LPS) in conscious female rats with different hormonal states were determined. In contrast to no effects in sham-operated females, treatment of OVX rats with LPS (i) decreased BP, (ii) increased spectral low-frequency/high-frequency ratio of HRV, denoting enhanced cardiac sympathetic dominance, (iii) attenuated reflex tachycardic responses to sodium nitroprusside, and (iv) increased systolic contractility (dP/dt_max). The developed hypotension was (i) fully eliminated in estrogen (E₂)-pretreated OVX rats, (ii) partially counteracted after selective activation of estrogen receptor-α (PPT) or β (DPN). All estrogenic compounds abrogated LPS enhancement of cardiac sympathetic drive. However, PPT was more successful than E2 or DPN in compromising LPS depression in baroreflex activity and elevation in dP/dt_max. Molecular studies showed that PPT was most effective in attenuating the upregulated myocardial expressions of NF-κB and iNOS in endotoxic OVX rats. Myocardial expression of the defensive HSP70 was comparably increased by all estrogenic products. Except for improved cardiac spectral activity, none of these functional or molecular entities was affected by medroxyprogesterone acetate (MPA). Overall, our data suggest diverse therapeutic advantages for gonadal hormones in the worsened endotoxic complications in rats with surgical menopause, with probably more favorable role for ERα agonism within this context.

The estrogen-macrophage interplay in the homeostasis of the female reproductive tract

BACKGROUND

Estrogens are known to orchestrate reproductive events and to regulate the immune system during infections and following tissue damage. Recent findings suggest that, in the absence of any danger signal, estrogens trigger the physiological expansion and functional specialization of macrophages, which are immune cells that populate the female reproductive tract (FRT) and are increasingly being recognized to participate in tissue homeostasis beyond their immune activity against infections. Although estrogens are the only female gonadal hormones that directly target macrophages, a comprehensive view of this endocrine-immune communication and its involvement in the FRT is still missing.

OBJECTIVE AND RATIONALE

Recent accomplishments encourage a revision of the literature on the ability of macrophages to respond to estrogens and induce tissue-specific functions required for reproductive events, with the aim to envision macrophages as key players in FRT homeostasis and mediators of the regenerative and trophic actions of estrogens.

SEARCH METHODS

We conducted a systematic search using PubMed and Ovid for human, animal (rodents) and cellular studies published until 2018 on estrogen action in macrophages and the activity of these cells in the FRT.

OUTCOMES

Our search identified the remarkable ability of macrophages to activate biochemical processes in response to estrogens in cell culture experiments. The distribution at specific locations, interaction with selected cells and acquisition of distinct phenotypes of macrophages in the FRT, as well as the cyclic renewal of these properties at each ovarian cycle, demonstrate the involvement of these cells in the homeostasis of reproductive events. Moreover, current evidence suggests an association between estrogen-macrophage signaling and the generation of a tolerant and regenerative environment in the FRT, although a causative link is still missing.

WIDER IMPLICATIONS

Dysregulation of the functions and estrogen responsiveness of FRT macrophages may be involved in infertility and estrogen- and macrophage-dependent gynecological diseases, such as ovarian cancer and endometriosis. Thus, more research is needed on the physiology and pharmacological control of this endocrine-immune interplay.

Sexual dimorphism in bacterial infections

Background

Sex differences are important epidemiological factors that impact in the frequency and severity of infectious diseases. A clear sexual dimorphism in bacterial infections has been reported in both humans and animal models. Nevertheless, the molecular mechanisms involved in this gender bias are just starting to be elucidated. In the present article, we aim to review the available data in the literature that report bacterial infections presenting a clear sexual dimorphism, without considering behavioral and social factors.

Main body

The sexual dimorphism in bacterial infections has been mainly attributed to the differential levels of sex hormones between males and females, as well as to genetic factors. In general, males are more susceptible to gastrointestinal and respiratory bacterial diseases and sepsis, while females are more susceptible to genitourinary tract bacterial infections. However, these incidences depend on the population evaluated, animal model and the bacterial species. Female protection against bacterial infections and the associated complications is assumed to be due to the pro-inflammatory effect of estradiol, while male susceptibility to those infections is associated with the testosterone-mediated immune suppression, probably via their specific receptors. Recent studies indicate that the protective effect of estradiol depends on the estrogen receptor subtype and the specific tissue compartment involved in the bacterial insult, suggesting that tissue-specific expression of particular sex steroid receptors contributes to the susceptibility to bacterial infections. Furthermore, this gender bias also depends on the effects of sex hormones on specific bacterial species. Finally, since a large number of genes related to immune functions are located on the X chromosome, X-linked mosaicism confers a highly polymorphic gene expression program that allows women to respond with a more expanded immune repertoire as compared with men.

Conclusion

Notwithstanding there is increasing evidence that confirms the sexual dimorphism in certain bacterial infections and the molecular mechanisms associated, further studies are required to clarify conflicting data and to determine the role of specific hormone receptors involved in the gender bias of bacterial infections, as well as their potential as therapeutic targets.

Gonadal hormone receptors underlie the resistance of female rats to inflammatory and cardiovascular complications of endotoxemia

The male gender is more vulnerable to immunological complications of sepsis. Here, we tested the hypotheses that female rats are protected against endotoxemia-evoked hypotension and cardiac autonomic dysfunction, and that gonadal hormone receptors account for such protection. Changes in blood pressure, heart rate, and cardiac sympathovagal balance caused by i.v. lipopolysaccharide (LPS) were determined. In male rats, LPS elevated serum TNFα together with falls in blood pressure and rises in heart rate. The spectral index of cardiac sympathovagal balance (low-frequency/high-frequency ratio, LF/HF) was reduced by LPS, suggesting an enhanced parasympathetic dominance. Remarkably, none of these LPS effects was evident in female rats. We also report that pretreatment of female rats with fulvestrant (nonselective estrogen receptor blocker), PHTPP (estrogen receptor β blocker), or mifepristone (progesterone receptor blocker) uncovered clear inflammatory (increased serum TNFα), hypotensive and tachycardic responses to LPS. However, these female rats, contrary to their male counterparts, exhibited increases in LF/HF ratio. On the other hand, LPS failed to modify inflammatory or cardiovascular states in rats pretreated with MPP (estrogen receptor α blocker). In females treated with formestane (aromatase inhibitor), LPS increased LF/HF ratio but had no effect on blood pressure. In male rats, the hypotensive and cardiac autonomic effects of LPS were (i) eliminated after treatment with estrogen, and (ii) intensified and inhibited, respectively, in flutamide (androgen receptor blocker)-pretreated rats. These findings highlight important roles for female gonadal hormones and functional estrogen receptor β and progesterone receptors in offsetting inflammatory and cardiovascular derangements caused by endotoxemia in female rats.

Innate Sex Bias of Staphylococcus aureus Skin Infection Is Driven by α-Hemolysin

Numerous studies have reported sex bias in infectious diseases, with bias direction dependent on pathogen and site of infection. Staphylococcus aureus is the most common cause of skin and soft tissue infections (SSTIs), yet sex bias in susceptibility to S. aureus SSTI has not been described. A search of electronic health records revealed an odds ratio of 2.4 for S. aureus SSTI in males versus females. To investigate the physiological basis of this bias, we compared outcomes between male and female mice in a model of S. aureus dermonecrosis. Consistent with the epidemiological data, female mice were better protected against SSTI, with reduced dermonecrosis followed later by increased bacterial clearance. Protection in females was disrupted by ovariectomy and restored by short-term estrogen administration. Importantly, this sex bias was mediated by a sex-specific response to the S. aureus-secreted virulence factor α-hemolysin (Hla). Infection with wild-type S. aureus suppressed inflammatory cytokine production in the skin of female, but not male, mice when compared with infection with an isogenic hla deletion mutant. This differential response was conserved following injection with Hla alone, demonstrating a direct response to Hla independent of bacterial burden. Additionally, neutrophils, essential for clearing S. aureus, demonstrated sex-specific S. aureus bactericidal capacity ex vivo. This work suggests that sex-specific skin innate responsiveness to Hla and neutrophil bactericidal capacity play important roles in limiting S. aureus SSTI in females. Understanding the molecular mechanisms controlling this sex bias may reveal novel targets to promote host innate defense against S. aureus skin infection.

Role of testosterone in regulating induction of TNF-α in rat spleen via ERK signaling pathway

Spleen is a pivotal organ for regulating immune homeostasis. It has been shown that testosterone diminishes secretion of various inflammatory molecules under multiple conditions. However, the mechanisms of action of endogenous testosterone affecting immune responses in the spleen remain unknown. The aim of the present study was to evaluate the immune functions of the spleen in response to testosterone withdrawal after orchidectomy, and the impact of splenocytes on the bacterial endotoxin lipopolysaccharide (LPS)-induced secretion of inflammatory molecules. Male rats were divided into 3 groups, i.e. intact, orchidectomized (Orch) and orchidectomized plus replacement of testosterone propionate (TP) (Orch+TP). The Orch and Orch+TP rats underwent bilateral orchidectomy one week before TP replacement (2mg/kg body weight) or sesame oil in intact rats as controls for seven days. Orch resulted in a significant increase of spleen weight and basal secretion of nitric oxide (NO) from splenocytes. Additionally, LPS up-regulated cell proliferation and the secretion of tumor necrosis factor-alpha (TNF-α) in splenocytes of Orch rats. Orch further up-regulated phosphorylation of extracellular signal-regulated kinases. Interestingly, the plasma corticosterone concentration in the Orch group was higher than that in the intact and Orch+TP groups. Deficiency of testosterone-elevated TNF-α and NO secretion in response to LPS were confirmed in the rat splenocytes. Testosterone also significantly attenuated LPS-elicited release of TNF-α and NO in a dose-dependent manner. However, testosterone did not suppress splenic blastogenesis at doses in the 10(-10)-10(-7)M concentration range. In this context, testosterone might have a protective role against inflammatory responses in the spleen. The present study provides evidence to indicate that testosterone might modulate the immune system.