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Proc Natl Acad Sci U S A. Nov 23, 2004; 101(47): 16695–16700.
Published online Nov 16, 2004. doi:  10.1073/pnas.0407550101
PMCID: PMC534518
Physiology

Impaired adrenal stress response in Toll-like receptor 2-deficient mice

Abstract

Septicemia is one of the major health concerns worldwide, and rapid activation of adrenal steroid release is a key event in the organism's first line of defense during this form of severe illness. The family of Toll-like receptors (TLRs) is critical in the early immune response upon bacterial infection, and TLR polymorphisms are frequent in humans. Here, we demonstrate that TLR-2 deficiency in mice is associated with reduced plasma corticosterone levels and marked cellular alterations in adrenocortical tissue. TLR-2-deficient mice have an impaired adrenal corticosterone release after inflammatory stress induced by bacterial cell wall compounds. This defect appears to be mediated by a decrease in systemic and intraadrenal cytokine expression, including IL-1, tumor necrosis factor α, and IL-6. Our data demonstrate a link between the innate immune system and the endocrine stress response. The critical role of TLR-2 in adrenal glucocorticoid regulation needs to be considered in patients with inflammatory disease.

Keywords: endotoxemia, inflammation, glucocorticoids, immune response

In the U.S., the incidence of sepsis has been found to be three cases per 1,000 people, which translates into 750,000 cases per year. The overall mortality is ≈30% rising up to 80% in patients with multiple conditions (1). During sepsis, relative adrenal insufficiency may occur in a substantial number of patients and is responsible for increased mortality. Replacement therapy with low-dose hydrocortisone during septic shock or acute respiratory distress syndrome showed improved survival (24). At present, inadequate adrenal function and glucocorticoid treatment during sepsis is one of the most discussed topics in medicine.

Evidence does however indicate that an intact adrenal stress response is critical for a host's defense to infection (57). There is good evidence that impaired innate immunity mediated by Toll-like receptors (TLRs) is involved in sepsis and cardiovascular disease in humans (810). The initial host defense against bacterial infection by the innate immune system is essentially initiated by TLRs, family-pattern-recognition receptors for the detection and response to microbial ligands. Recently, we have described the expression of TLR-2 and TLR-4 in human adrenals (11). New data demonstrate the existence of TLR mutations in humans, with a TLR-2 polymorphism being more frequent than previously estimated (12). Therefore, we studied specifically the TLR-2 pathway and the adrenal stress system under conditions of bacterial cell wall fragment challenge, an experimental scenario associated with the pathophysiology of sepsis.

In addition to hypothalamic hormones, including corticotropin-releasing hormone and vasopressin, inflammatory cytokines, such as IL-1, IL-6, and tumor necrosis factor α (TNF-α), have been identified as important modulators of hypothalamic–pituitary–adrenal (HPA) axis function (5, 6). During inflammation, these cytokines are capable of maintaining high glucocorticoid output, suggesting a shift from neuroendocrine to immune-endocrine regulation of the adrenal (13). Therefore, a coordinated response of the adrenal and immune system is crucial for survival during severe inflammation (1416).

As cytokines are important in the regulation of the HPA axis, we hypothesized that the TLR system might play a key role in inducing an adrenal stress response after inflammatory stimuli. It has long been known that unresponsiveness to lipopolysaccharide (LPS), which later was found to be due to a genetic TLR-4 defect, leads to increased susceptibility to infection (17, 18). In addition, recent studies have shown that mice with a targeted disruption of the TLR-2 gene are more susceptible to meningitis-induced intracranial complications (16). In addition, TLR-2 deficient (TLR-2–/–) mice have a more pronounced reduction in body weight and a deterioration of motor function impairment after experimental pneumococcal infection (19). Likewise TLR-2–/– mice succumb to Mycobacterium tuberculosis infection (20) and are highly susceptible to Staphylococcus aureus infection (21).

Several studies have described the existence of TLR mutations in humans (for review, see refs. 2224). A recent study reported a rate of nearly 10% heterozygosity for the TLR-2 Arg753Gln polymorphism (12). The role of TLR-2 in the endocrine stress response during development and progression of inflammatory complications, however, has, to our knowledge, not been investigated to date. Therefore, we performed a comprehensive analysis of adrenal function in TLR-2–/– mice under normal conditions and after activation by bacterial lipids, i.e., lipoteichoic acid (LTA) and LPS.

Materials and Methods

Animals and Treatments. TLR-2–/– mice were generated by homologous recombination (Deltagen, Menlo Park, CA) and kindly provided by Tularik (South San Francisco, CA). WT (C57BL/6) and TLR-2–/– mice were housed under standard conditions (55% humidity, 12-h day/night rhythm, standard chow and water ad libitum). All procedures were carried out in accordance with the Association for Assessment and Accreditation of Laboratory Animal Care International guidelines and Guide for the Care and Use of Laboratory Animals (Department of Health and Human Services, National Institutes of Health, Publication No. 86-23) and were approved by the ethical and research board of the University and county of Düsseldorf. Animals (age, 12–16 weeks) were randomized (n = 8 per group) and treated where indicated with LPS (i.p.; 1 mg/kg; Escherichia coli, serotype 0.111:B4, Sigma–Aldrich), LTA (i.p; 1 mg/kg; Staphylococcus aureus, Sigma–Aldrich) (25, 26) or saline (i.p.) for 6 or 24 h, after which animals were killed by terminal pentobarbital anesthesia (Sigma–Aldrich, prepared by the University of Düsseldorf pharmacy).

Western Blotting. Tissue or cells were lysed in ice-cold buffer (150 mM NaCl/50 mM Tris·HCl, pH 7.4/1 mM EDTA/5 μg/ml leupeptin/5 μg/ml aprotinin A/1 mM PMSF/0.1% SDS/1% sodium deoxycholate/1% Triton X-100). After brief centrifugation (20,000 × g), supernatants were removed, total protein was determined (bicinchoninic acid method), separated by SDS/PAGE and blotted onto nitrocellulose membranes. The blots were probed with anti-TLR-2 antibody (1:1,000; S-16, Santa Cruz Biotechnology) and with horseradish peroxidase-conjugated anti-goat secondary antibody (1:3,000; Santa Cruz Biotechnology). Signals were visualized by enhanced chemiluminescence.

Electrophoretic Mobility Shift Assay and Apoptosis Detection. Adrenal extracts were prepared in high-salt buffer (20 mM Hepes, pH 7.9/350 mM NaCl/20% glycerol/1% Nonidet P-40/1 mM MgCl2/0.5 mM EDTA/0.1 mM EGTA/0.5 mM DTT/1 mM PMSF/2 μg/ml aprotinin/2 μg/ml leupeptin), cleared by centrifugation at 17,500 × g for 20 min at 4°C and assayed for protein concentration (bicinchoninic acid assay). Equal amounts (5 μg) were incubated with the 32P-end-labeled NF-κB-specific oligonucleotide (10,000 cpm) for 20 min at room temperature in 20 μl of total volume containing 10 mM Hepes, pH 7.5/10 mM KCl/0.2 mM DTT/0.5 mM MgCl2/10% glycerol/1 μg poly(dI-dC)/2 μg BSA. The samples were separated on 4% nondenaturing polyacrylamide gels and quantified by PhosphorImager analysis. Apoptosis was detected by using terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling with the ApopTag peroxidase in situ detection kit (Chemicon) according to the manufacturer's instructions.

Immunohistochemistry. Adrenal tissue was fixed in 4% paraformaldehyde and processed as described in ref. 27. We incubated 10-μm sections overnight with the following primary antisera: goat anti-mouse TNF-α (R & D Systems), goat anti-mouse/rat TLR-2 (Santa Cruz Biotechnology), goat anti-mouse IL-1 receptor (Santa Cruz Biotechnology), and rabbit anti-mouse IL-6 (Chemicon). For detection of primary antibodies, a horseradish peroxidase system was used (DAKO), and the signal was visualized with diaminobenzidine.

Morphometric Analysis. Morphometric analysis to determine the size of adrenal sections was performed by using a computer-supported imaging system connected to a light microscope [Eclipse TE300 microscope (Nikon), lucia g Software (Nikon), Jerome Industry Phototype P99135 camera (Digital Video Camera, Austin, TX)]. The area of a number of sections was measured in triplicate for each section. The four largest sections were evaluated to give an approximation of the longest diameter in each gland.

Electron Microscopy. Adrenal glands (n = 3 per group) were fixed in 2% formaldehyde and 2% glutaraldehyde in 0.1 M phosphate buffer, pH 7.3. Tissue slices were postfixed for 90 min (2% OsO4 in 0.1M cacodylate buffer, pH 7.3), dehydrated in ethanol, and embedded in epoxy resin. Ultrathin sections were stained with uranyl acetate and lead citrate and examined at 80 kV in a CM 10 electron microscope (Philips, Eindhoven, the Netherlands).

Plasma Corticosterone, Adrenocorticotropic Hormone (ACTH), and Cytokine Levels. Plasma corticosterone and ACTH levels were determined by RIA (Diagnostic Systems Laboratories, Webster, TX). The levels of IL-1β, IL-6, and TNF-α were determined by ELISA according to instruction manuals (R & D Systems).

Statistical Analysis. Data was analyzed by Student's t test or ANOVA by using prism software (GraphPad, San Diego). Results are presented as the mean ± SEM. Statistical significance was defined as P < 0.05.

Results

Adrenal Structure and Function in TLR-2/. WT mouse adrenal cells expressed TLR-2 as demonstrated by Western blot analysis (Fig. 1A), whereas TLR-2 protein was absent in TLR-2–/– mice (Fig. 1 A). The adrenal gland was significantly larger in TLR-2–/– mice (213 ± 18.7 mm) than in WT animals (115 ± 3.1 mm, P < 0.001) (Fig. 1B). This increase was primarily due to the enlargement of the adrenal cortex and not the adrenal medulla. To compare parameters of cell turnover in the adrenal cortex, we investigated the occurrence of apoptosis in both groups. Apoptotic rate as demonstrated by in situ end labeling and electron microscopy did not differ between WT and TLR-2–/– mice (data not shown). Adrenal corticosterone production in TLR-2–/– vs. WT mice was moderately decreased (105 ± 11.4 vs. 74.5 ± 8.3 ng/ml; P < 0.05) (Fig. 1C). In contrast, plasma ACTH levels were elevated in TLR-2–/– mice (WT, 78 ± 9.5 pg/ml vs. TLR-2–/–, 127 ± 26 pg/ml; P = 0.11) (Fig. 1D), suggesting a potential primary impairment of the HPA axis at the level of the adrenal gland.

Fig. 1.
Adrenal structure and function in TLR-2–/– mice. (A) TLR-2 expression in adrenal lysates from WT and TLR-2–/– mice analyzed by Western blot analysis. (B) Adrenal surface in TLR-2–/– (n = 3) and WT (n = 5) ...

At the ultrastructural level, adrenocortical cells of TLR-2–/– mice exhibited marked morphological alterations (Fig. 1 FH). In WT animals, the most prominent organelles in steroid-producing adrenocortical cells were round mitochondria with characteristic tubulovesicular internal membranes and numerous lipid-storing droplets constituting the substrates for steroidogenesis (Fig. 1E). In TLR-2–/– mice, there was a decrease in the number of mitochondria with a transformation of vesicular internal membranes to more tubular structures bridging the inner matrix (Fig. 1F). The most conspicuous changes, however, occurred at the cell membranes of adrenocortical cells in TLR-––/– mice. Although normal adrenocortical cells have the capacity to form filopodia under stimulation, changes in the plasma membrane of adrenocortical cells of TLR-2–/– mice were distinct and occurred under basal conditions (Fig. 1 FH). There were extensive interdigitations and in-folds (Fig. 1 FH) engulfing cytoplasm, intracytoplasmic organelles, or extracellular structures, including nerve endings (Fig. 1H). In part, the abundant membrane folding appeared to form stratifications or vesicularization of membranes, providing a complex labyrinth formed by interdigitating processes (Fig. 1H).

Plasma Corticosterone and ACTH Response After i.p. LPS and LTA Injection. After LPS stimulation (6 h), WT mice exhibited a 3-fold increase in the release of adrenal glucocorticoids as compared with a saline control (94.6 ± 19.3 vs. 306.3 ± 22.5 ng/ml; P < 0.0001). This increase in plasma corticosterone levels was significantly higher in WT than in TLR-2–/– mice (P < 0.001), which only showed a 2-fold increase (Fig. 2A). The rise in adrenal glucocorticoid release was accompanied by a 3-fold increase in plasma ACTH levels in WT mice, suggesting a central activation of the HPA axis (67.47 ± 8 vs. 216.5 ± 48 pg/ml; P = 0.02) (Fig. 2B). In contrast, the adrenal ACTH response to LPS in TLR-––/– mice was blunted (Fig. 2B).

Fig. 2.
Plasma corticosterone and ACTH response after i.p. LPS and LTA injection. (A) Plasma corticosterone 6 h after LPS injection in WT animals (n = 8) and TLR-2–/– mice (n = 7). (B) Plasma ACTH levels 6 h after LPS injection in WT animals ( ...

Plasma corticosterone levels were not affected by LTA in WT animals during the first 6 h (Fig. 2C). Conversely, there was a significant reduction of plasma corticosterone levels in TLR-––/– mice 6 h after LTA injection (79 ± 13 vs. 42 ± 7.8 ng/ml; P < 0.05) (Fig. 2C). LTA had no significant effect on ACTH levels in WT or TLR-2–/– mice (Fig. 2D).

After LPS injections (24 h), plasma corticosterone levels returned almost to baseline levels. However, plasma corticosterone levels remained significantly lower in TLR-2–/– mice when compared with WT animals (130.9 ± 12.4 vs. 70.2 ± 13.4 ng/ml; P < 0.01) (Fig. 2E). ACTH levels did not differ in either groups 24 h after LPS injection (Fig. 2F). Plasma corticosterone levels were significantly reduced in WT mice by ≈40% 24 h after LTA injections, whereas there was no significant further decrease in TLR-2–/– mice (WT, 131.7 ± 13.3 vs. 77.8 ± 9.2 ng/ml, P < 0.01; TLR-2–/–, 83.6 ± 15.8 vs. 70.2 ± 13.4 ng/ml, P = 0.38) (Fig. 2G). Plasma ACTH levels were not significantly different in WT and TLR-2–/– animals 24 h after LTA injections (Fig. 2H).

Adrenal NF-κB Activation and Cellular Stress Response After LPS and LTA Injection. NF-κB activation in the adrenals of WT and TLR-2–/– mice was determined by electrophoretic mobility shift assay. LPS and LTA treatment in WT mice led to strong induction of NF-κB DNA-binding activity in adrenal cells. In contrast, NF-κB activation was considerably reduced in TLR-––/– mice, and the LTA response was blunted. LPS-induced activation of adrenal NF-κB was preserved in TLR-2–/– mice (Fig. 3 A and B).

Fig. 3.
Adrenal NF-κB activation and cellular stress response after i.p. LPS and LTA injection. (A) NF-κB activation was analyzed by electrophoretic mobility shift assay in adrenal protein extracts from WT and TLR-2–/– mice (n ...

Steroidogenesis takes place in mitochondria and the smooth endoplasmic reticulum (SER) in the steroid-producing cells. On the ultrastructural level, there was a marked increase in the number of mitochondria as well as in vesicularization in the adrenocortical cells of WT animals 24 h after LPS challenge (Figs. (Figs.1E1E and and3C).3C). This increase in mitochondria, SER, and vesicularization of mitochondrial membranes is consistent with the increase in steroidogenesis. At the same time, the number of liposomes declined in accordance with the utilization of stored cholesterol pools as a substrate for glucocorticoid synthesis (Fig. 3C). This process of increased SER, mitochondrial membranes and reduced liposomes was markedly less pronounced in TLR-––/– mice, commensurate with their impaired steroid release (Figs. (Figs.1F1F and and3D3D).

Impaired Cytokine Response in TLR-2/ Mice. After LPS challenge (6 h), there was a significant increase in inflammatory cytokine level(s) detectable in WT animals. IL-1 exhibited a 3-fold increase in plasma levels (36 ± 0.55 vs. 114 ± 19.27 pg/ml; P < 0.01) (Fig. 4A). The plasma levels of TNF-α increased >2-fold (55 ± 0.9 vs. 131 ± 26 pg/ml; P < 0.05) (Fig. 4B), whereas plasma levels of IL-6 were almost 1,000-fold elevated in WT mice challenged with LPS for 6 h (39 ± 3 vs. 3,574 ± 13 pg/ml; P < 0.001) (Fig. 4C). Whereas IL-1 and TNF-α levels returned to baseline levels 24 h after LPS challenge (data not shown), IL-6 levels remained elevated in WT animals (36.8 ± 1.7 vs. 3,012 ± 414 pg/ml; P < 0.001) (Fig. 4D). In contrast to WT mice, the response of all three cytokines was significantly reduced in TLR-2–/– mice. LPS challenge (6 h) did not trigger a strong increase in the plasma levels of IL-1 (38 ± 5.4 vs. 50 ± 4.5 pg/ml) (Fig. 4A) and TNF-α (56 ± 1.5 vs. 83 ± 5.8 pg/ml; P = 0.01) (Fig. 4B) in TLR-2–/– mice. However, the IL-6 response in these animals was still preserved (Fig. 4C). Nevertheless, 24 h after LPS challenge, IL-6 induction was significantly reduced in TLR-2–/– mice (44 ± 3.5 vs. 628 ± 240.5 pg/ml; P = 0.09) compared with WT animals (36.5 ± 1.7 vs. 3,012 ± 414.6 pg/ml; P < 0.001) (Fig. 4D). LTA challenge did not significantly affect systemic IL-1, IL-6, or TNF-α levels in WT or TLR-2–/– animals at either time point (Fig. 4).

Fig. 4.
Plasma cytokine levels in TLR-2–/– mice in response to LPS and LTA treatment. WT mice and TLR-2–/– mice (n = 5–8 per group) were treated as indicated with saline (sal), LPS, or LTA for the indicated amounts of time ...

Intraadrenal Stress Response and Cytokine Expression. Because the local production of cytokines and cytokine receptors in the adrenal gland has been implicated in the regulation of steroidogenesis, we have further analyzed the expression of TNF-α, IL-6, and IL-1 receptor on adrenocortical cells of WT and TLR-2–/– mice by immunohistochemistry. There was only a weak constitutive staining for IL-1 receptor, TNF-α, and IL-6 on adrenocortical cells in WT animals (Fig. 5 AC). LPS treatment resulted in a marked increase in the expression of IL-1 receptor, IL-6, and TNF-α protein (Fig. 5 DF). In contrast, in LPS-treated TLR-2–/– mice, staining for IL-1 receptor, IL-6, and TNF-α (Fig. 5 GI) was markedly reduced as compared with WT animals exposed to the same LPS treatment. No significant expression for IL-1 or IL-18 was observed on adrenocortical cells of WT or TLR-2–/– mice challenged with saline or LPS (data not shown).

Fig. 5.
Detection of IL-1 receptor, IL-6, and TNF-α expression in adrenal cortices. (A and D) After LPS treatment (24 h), adrenal cortices of WT mice were analyzed for immunoreactivity for the IL-1 receptor (IL-1 R). (Magnification, ×40.) (B and ...

Discussion

This study demonstrates an important role for TLR-2 in the adrenal stress response. TLR-2 is expressed in both mouse and human adrenal glands under basal conditions. Absence of this receptor is associated with an enlargement of the adrenal gland and a reduction in corticosterone levels. Furthermore, plasma ACTH levels are elevated in TLR-2–/– mice, which indicates a possible impairment of the HPA axis at the level of the adrenal gland, even under basal conditions. Our ultrastructural analysis of adrenocortical cells indicates that TLR-2–/– mice also have marked changes at the level of the plasma membrane with unusual interdigitations and infoldings of cell membranes.

Under basal conditions, impairment of adrenal structure and function in TLR-2–/– mice was only mild and did not compromise the viability of the animals. However, an appropriate adrenal glucocorticoid response to inflammatory stimuli is critical for the organism to cope with disease. Therefore, we evaluated the adrenal stress response after activation of the HPA axis by bacterial ligands, including LPS and LTA. Recent evidence suggests that the release of inflammatory cytokines, including IL-1, IL-6, and TNF-α, from immune cells or fibroblasts is impaired in TLR-2–/– mice after exposure to inflammatory stimuli (28, 29).

Immune activation of the adrenal gland by LPS is thought to occur by cytokine stimulation of corticotropin-releasing hormone release from the median eminence of the hypothalamus, which, in turn, stimulates the secretion of ACTH from the pituitary and adrenal cortisol release. In this mechanism, nitric oxide plays a key role in inducing the changes in release of hypothalamic peptides induced by cytokines during infection (3032). LPS has been used in most studies analyzing the interaction of the HPA axis with the immune system as a model for inflammation. Therefore, we first tested the effect of LPS, although LPS is known to be a TLR-4 ligand, in our TLR-2–/– mice. Interestingly, in the absence of TLR-2, the systemic response of all three inflammatory cytokines (IL-1, TNF-α, and IL-6) was significantly impaired compared with WT animals. There was a blunted IL-1 response in TLR-2–/– animals to LPS, which might account for the impairment of the HPA axis. IL-1 can activate the HPA axis at the central and peripheral level (5, 6, 3335). Aberrant expression of IL-1 receptors on adrenal cells has even been implicated in Cushing's syndrome (27). Because LPS induces the synthesis and secretion of IL-1, it has been proposed that IL-1 is the primary endogenous mediator in the response to LPS. However, by using a wide range of doses of the IL-1-receptor antagonist protein (IL-1Ra) at various times after i.p. LPS challenge, no significant alterations in plasma ACTH and corticosterone levels have been observed (36). Therefore, a blunted IL-1 response may not be the primary mechanism responsible for the impaired adrenal release of glucocorticoids after LPS stimulation in TLR-2–/– mice. Similarly, TNF-α has been demonstrated to have a direct inhibitory action on adrenal cells and, hence, an impaired TNF-α response would be expected to lead to an elevation of corticosterone levels in TLR-2–/– mice, rather than the blunted response that was observed.

Finally, IL-6 is an essential corticotropin-releasing hormone-independent stimulator of the adrenal axis during immune activation (37). IL-6 receptors are present on pituitary corticotrophic and adrenocortical cells, which is consistent with the ability of IL-6 to augment adrenal function (37). After LPS injection, plasma corticosterone levels in IL-6–/– mice were ≈30% lower compared with WT animals. In our model of TLR-2–/– mice plasma, the observed increase in corticosterone levels was 60% lower compared with WT animals. Consistent with a potential role of intraadrenal IL-6, we observed a reduced number of IL-6-positive cells in TLR-2–/– mice after LPS treatment. Altogether, there is a marked impairment of both systemic and local cytokine release, which explains the significant attenuation of the HPA axis in TLR-2–/– mice upon stimulation with bacterial ligands. It cannot, however, be ruled out that some of the effects observed in our study after LPS stimulation are due to a contamination of commercially available LPS with lipopeptides.

One of the classic ligands for TLR-2 is LTA, which is found in the cell wall of Gram-positive bacteria. This study demonstrates a significant impairment in adrenal glucocorticoid release after exposure to LTA. Interestingly, LTA significantly suppressed corticosterone levels in TLR-2–/– mice 6 h after injection and only after 24 h in WT animals. In future experiments, however, higher doses of LTA should also be tested and may elicit more prominent effects. Because there was no significant impairment at the level of the pituitary in the current experiments, the impaired glucocorticoid response may suggest a direct action at the level of the adrenal gland.

Similar to the Toll-like family of receptors, the steroid system predates the animal kingdom and is remarkably preserved through the evolutionary process. The capacity to respond to external and internal stimuli with a rapid and efficient endocrine stress response has been a critical step for the survival and evolution of higher organisms. The adrenal has an astonishing capacity to adapt to physiological stressors or disease with extensive hypervascularization, zonal transformation, cellular hyperplasia, and rapid hormone release (38). In turn, TLRs and, in particular, TLR-2 have a fundamental role in coordinating the organism's first line of acute defense against tissue injury or infection. Therefore, the functional integration of the immune system and the stress system by means of TLR-2 may have been programmed early in evolution, resulting in a coordinated and efficient regulation of both systems. We demonstrate that TLR-2 plays an important role in the HPA axis. These findings may help to understand more about immunity and the stress system. Thus, TLR-2 and, possibly, TLR-4 may constitute an important link between the immune and endocrine stress systems at both the central and peripheral levels, particularly during inflammation and sepsis (Fig. 6). Furthermore, in view of the potential of selective therapeutic targeting of TLRs, the close link of TLR-2 with the function of the HPA axis needs to be considered.

Fig. 6.
Artistic rendition depicting potential immune–endocrine interaction mediated by TLR-2 and TLR-4 during inflammation and sepsis. CRH, corticotropin-releasing hormone.

Based on our studies, it should be of high priority to test adrenal function particularly in patients with polymorphisms in the TLR system. Mutations in the innate immune system are not a rare event and may be the underlying mechanism for an impaired adrenal stress response in patients with sepsis.

Acknowledgments

We thank D. Wiese, H. Sommerfeld, and A. Tries for excellent technical assistance. This work was supported by Deutsche Forschungsgemeinschaft Grants BO 1141/7-1 (to S.R.B.) and ZA 243/8-1 (to K.Z.) and a grant from the Pinguin Foundation (to K.Z.).

Notes

Abbreviations: TLR, Toll-like receptor; TNF-α, tumor necrosis factor α; HPA, hypothalamic–pituitary–adrenal; LPS, lipopolysaccharide; LTA, lipoteichoic acid; ACTH, adrenocorticotropic hormone.

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