Hormonal influence on experimental infections by a toxic shock strain of Staphylococcus aureus

Immunomodulatory Effects of 17β-Estradiol on Epithelial Cells during Bacterial Infections

The innate immune system can function under hormonal control. 17β-Estradiol (E2) is an important sexual hormone for the reproductive cycle of mammals, and it has immunomodulatory effects on epithelial cells, which are the first line of defense against incoming bacteria. E2 regulates various pathophysiological processes, including the response to infection in epithelial cells, and its effects involve the regulation of innate immune signaling pathways, which are mediated through estrogen receptors (ERs). E2 modulates the expression of inflammatory and antimicrobial elements such as cytokines and antimicrobial peptides. The E2 effects on epithelial cells during bacterial infections are characterized by an increase in the production of antimicrobial peptides and by the diminution of the inflammatory response to abrogate proinflammatory cytokine induction by bacteria. Here, we review several novel molecular mechanisms through which E2 regulates the innate immune response of epithelial cells against bacterial infections.

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.

Does sex affect 30-day mortality in Staphylococcus aureus bacteremia?

BACKGROUND

Sex-related differences in complications and mortality of infection were examined with conflicting results. Further studies are required to bring new light in this topic in Staphylococcus aureus infections.

OBJECTIVE

We examined the outcomes of S. aureus infection in men and in women and whether sex-related differences were explained by underlying disorders, severity of disease, or clinical management.

METHODS

This cohort study was conducted in a single center between 1988 and 2007. Patients with clinically significant S. aureus bacteremia were included. We compared 30-day all-cause mortality in men and women. We used multivariable logistic regression analysis to test whether sex was independently associated with mortality.

RESULTS

One thousand ninety-three patients were identified with S. aureus bacteremia. All-cause mortality at day 30 was 39.3% (508 of 1293 patients): 44.8% (238 of 531 patients) in women and 35.4% (270 of 762 patients) in men (P < 0.01). In a multivariate analysis, female sex was associated with higher mortality (odds ratio = 1.63; 95% CI, 1.07-2.47). The excess mortality in women was not explained by differences in demographic characteristic factors, background conditions, infection severity and management, or septic complications.

CONCLUSIONS

We found that women with S. aureus bacteremia had a greater risk of 30-day all-cause mortality than men, even when adjusting for other risk factors. However, we failed to explain this excess of mortality.

Persistent skin colonization with Staphylococcus aureus in atopic dermatitis: relationship to clinical and immunological parameters

BACKGROUND

Staphylococcus aureus has important implications for the pathogenesis of atopic dermatitis (AD). In some patients S. aureus can be eradicated from the skin during anti-inflammatory treatment, while in others bacterial colonization is persistent. Potential mechanisms and features of these two distinct groups of patients are not known.

OBJECTIVE

Accordingly, we studied relationships between the ability to eliminate S. aureus during an anti-inflammatory treatment and selected clinical and immunological features.

METHODS

Quantitative assessment of S. aureus on the skin, in nasal vestibule and throat, serum IgE levels, CD4/CD8 T-cell ratio, lymphocyte proliferation and phagocyte oxidative burst were determined during the exacerbation and after 4 and 12 weeks of the treatment using topical steroid and oral antihistamine in 34 patients with AD.

RESULTS

S. aureus was found on the skin of all 34 patients during exacerbation. Disease severity scoring of atopic dermatitis (SCORAD) correlated with the density of bacteria. Treatment with oral antihistamine and topical steroid resulted in a significant alleviation of symptoms, which correlated with the elimination of S. aureus from the skin in 70% of patients. In the remaining 30% of patients, dense (more than 10(10)/cm2) S. aureus skin colonization, persisted despite the treatment. Patients with persistent S. aureus presented with higher serum IgE levels, lower lymphocyte proliferation in response to staphylococcal enterotoxin B, phytohaemagluttinin and anti-CD3. Persistence of S. aureus was more common in men.

CONCLUSIONS

Patients with AD differ in the ability to clear S. aureus from the skin during anti-inflammatory treatment, which appears to be related to the abnormalities in immunological parameters. Local antibiotic therapy should be considered only in patients with persistent S. aureus colonization.

A CD-1 mouse model of infection with Staphylococcus aureus: Influence of gender on infection with MRSA and MSSA isolates

Staphylococcus aureus is an important pathogen of humans and other animals, causing bacteremia, abscessation, toxemia, and other infectious diseases. An animal model using CD-1 mice was developed to study the pathogenesis of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA). When inoculated into the CD-1 mouse model, it was shown that both MSSA isolates, (HR 78 and CSA-1) and MRSA isolates (MRSA 456 and MRSA 457) led to chronic infection of the kidney. Female CD-1 mice inoculated with MRSA 456 proved to be more susceptible to infection and mortality than their male counterparts. Castrated mice became more susceptible to infection than intact male mice, suggesting a hormonal involvement in the infection process.Key words: Staphylococcus aureus, animal model, gender, MSSA, MRSA.

Steroid sex hormones and macrophage function: regulation of chemiluminescence and phagocytosis

PROBLEM

Female sex hormones modulate a variety of humoral and cell-mediated immunologic functions. In this study, the effects of estrogen, progesterone, and testosterone on the chemiluminescence (CL) response and phagocytic ability of male rat peritoneal macrophages (M luminal diameter) were examined.

METHOD

In M luminal diameter pretreated with 10(-2) ng/ml of 17 beta-estradiol (E2) for 20 hours, the CL generated in response to phorbol myristate acetate (PMA), 1,2-dioctanoyl-rac-glycerol (C8:0), or opsonized zymosan (OZ) was significantly increased by 135%, 140%, and 136% of control values, respectively. In addition, M luminal diameter treated with 10(-5) ng/ml or 10 ng/ml of E2 exhibited a significantly greater PMA- or OZ-stimulated CL response than did untreated controls.

RESULTS

At 10(-2) ng/ml, progesterone enhanced and testosterone reduced the CL response, but these changes were not statistically significant. In time course studies, the PMA-stimulated CL response of M luminal diameter treated with 10(-2) ng/ml of E2 or progesterone for 5 h was significantly less than that of the untreated group. In the presence of endotoxin (12 pg/ml), the CL response in M luminal diameter treated with E2 or testosterone was significantly depressed as compared to untreated controls. Phagocytosis of opsonized sheep erythrocytes also was significantly enhanced (140% to 190% of control) when M luminal diameter were pretreated with 10(-12) M to 10(-8) M of either E2 or progesterone.

CONCLUSIONS

These findings suggest that, at physiological concentrations, E2 is capable of modulating both CL generation and phagocytic uptake by M luminal diameter in a manner not shared by other steroid hormones.

Oestrogen influences CD4+ T-lymphocyte activity in vivo and in vitro in beta 2-microglobulin-deficient mice

Oestrogen directly influences autoimmune diseases and the immune response to microbes. We studied the effect of oestrogen on CD4+ T cells specific for lymphocytic choriomeningitis virus (LCMV) using mice genetically engineered to be deficient in beta 2-microglobulin (beta 2m-/-). These mice are deficient in beta 2-microglobulin, class I major histocompatibility complex (MHC) molecules and CD8+ T lymphocytes. Fatal leptomeningitis after intracranial infection with LCMV is mediated by CD8+ cytotoxic T lymphocytes (CTL) in wild-type C57BL/6 mice, and by CD4+ T cells in beta 2m-/- mice. Male and female wild-type C57BL/6 mice showed equal susceptibility to immune meningitis. In contrast, male beta 2m-/- mice were less susceptible to fatal immune meningitis than were females. Orchidectomy and oestrogen treatment of male beta 2m-/- mice in vivo restored susceptibility to meningitis. The classic weight loss seen in beta 2m-/- mice after intracranial infection was also accentuated in females. Further, the in vitro activity of CD4+ T cells from male beta 2m-/- mice, as measured by CTL assays, was shown to be dependent on oestrogen. The natural killer cell activity of spleen cells from beta 2m-/- mice after infection with LCMV was not affected by oestrogen. These data demonstrate the influence of oestrogen on CD4+ T-cell activity both in vivo and in vitro.

Toxic shock syndrome

In the past 10 years, we have learned much about TSS and S. aureus and its toxins. A number of important biologic principles have been reemphasized in this first decade of TSS research: S. aureus is a very complex organism, one not likely to yield quick answers; in vitro observations must always be confirmed in the patient; animal models may not always be reliable replicates of human disease; and epidemiologic associations cannot be equated with causation. Toxic shock is an intricate phenomenon with many interesting scientific facets. Unraveling its mysteries will undoubtedly teach us more about the complex interaction of patients and microorganisms.

Synergistic induction of interleukin-1 by endotoxin and toxic shock syndrome toxin-1 using rat macrophages

We studied interleukin-1 (IL-1) secretion by rat peritoneal exudate macrophages stimulated with purified toxic shock syndrome toxin-1 (TSST-1). TSST-1 was observed to be a more potent inducer of IL-1 than was endotoxin. The induction of IL-1 secretion by TSST-1 was not blocked by polymyxin B but could be blocked by monoclonal antibodies directed against TSST-1. Synergistic induction of IL-1 was observed when the cells were stimulated with TSST-1 and endotoxin. The sequence of addition was found to be important for the synergistic response. Enhanced IL-1 production was observed only when macrophages were exposed to endotoxin before or simultaneously with TSST-1. Prior exposure of macrophages to TSST-1 had no enhancing effect on endotoxin-induced IL-1 secretion. We conclude that stimulation of the macrophage by endotoxin enhances the responsiveness of the cells to TSST-1 and may thereby play a role in the pathogenesis of toxic shock syndrome.