Osteopontin induces angiogenesis through activation of PI3K/AKT and ERK1/2 in endothelial cells

Angiogenesis is a key step in tumor growth and metastasis. The mechanism by which osteopontin (OPN) induces the angiogenesis of endothelial cells remains unclear. Here, we show that OPN confers cytoprotection through the activation of the PI3K/Akt pathway with subsequent upregulation of Bcl-xL and activation of nuclear factor-kappaB. OPN enhances the expression of vascular endothelial growth factor (VEGF) through the phosphorylation of AKT and extracellular signal-regulated kinase (ERK). In turn, OPN-induced VEGF activates PI3K/AKT and the ERK1/2 pathway as a positive feedback signal. Blocking the feedback signal by anti-VEGF antibody, PI3-kinase inhibitor or ERK inhibitor can partially inhibit the OPN-induced human umbilical vein endothelial cell (HUVEC) motility, proliferation and tube formation, while blocking the signal by anti-OPN or anti-alphavbeta3 antibody completely abrogates the biological effects of OPN on HUVECs. In addition, blood vessel formation is also investigated in vivo. The antiangiogenesis efficacy of anti-OPN antibody in vivo is more effective than that of anti-VEGF antibody, which only blocks the feedback signals. These data show that OPN enhances angiogenesis directly through PI3K/AKT- and ERK-mediated pathways with VEGF acting as a positive feedback signal. The results suggest that OPN might be a valuable target for developing novel antiangiogenesis therapy for treatment of cancer.

Living-related small bowel transplantation for three patients with short gut syndrome

OBJECTIVE

We summarized our experience of living-related small bowel transplantation and postoperative management of 3 patients with short gut syndrome.

METHODS

Patient #1, an 18-year-old boy, received a 150-cm segment of distal ileum with a vascular pedicle of distal superior mesenteric artery and vein, which was donated by his father. Patient #2, a 15-year-old boy, received a 160-cm graft of distal ileum from his mother. Patient #3, a 17-year-old boy, received a 170-cm graft of distal ileum from his father. The graft artery and vein were anastomosed to the recipient infrarenal aorta and vena cava, respectively, in end-to-side fashion using 7/0 Prolene suture. Intestinal continuity was restored by anastomosis of proximal end of the graft to the recipients' own proximal jejunum, the distal end was left open as a stoma. The recipient distal gut was anastomosed to the distal end of the graft. All 3 recipients were given FK506 (tacrolimus) regularly combined with periodic mycophenolate mofetil. In cases of acute rejection, large doses of steroids were administered to the recipients.

RESULTS

The recipients and donors had fairly unremarkable postoperative courses. So far, patient #1 has survived for 7 years and 6 months with a well-functioning graft and without requirement for total parenteral nutrition (TPN) support. His body weight increased 20 kg and of his life quality has dramatically improved. Patient #2, however, died of acute rejection with fatal sepsis at 5 months after transplantation. Patient #3 has survived for 3 years and 8 months enjoying a normal life. Postoperative recovery of all 3 donors was unremarkable. They were discharged 12 days after surgery without complications.

CONCLUSION

Outcomes of the implantation using the distal ileum as a graft in living-related small bowel transplantation have been satisfactory for both recipients and donors. It is feasible to anastomose the graft artery and vein to the recipient infrarenal aorta and vena cava. The intestinal continuity can be restored by a 1-stage strategy with minimal risk to the recipient. Appropriate application and adjustment of immune suppressors are crucial for the recipients to experience high-quality lives.

Parents Living with HIV in China: Family Functioning and Quality of Life

In China, HIV shifts the lifestyle of not only parents living with HIV/AIDS, but also their children, partners, and extended families. We examined factors related to the quality of life of parents living with HIV and the relation between family functioning and individual quality of life. Interviews were conducted with a total of 116 parents living with HIV/AIDS. Analyses of variance, Pearson correlations, and multiple regression analyses were performed to examine the relation between family functioning and quality of life. We found a significant association between family functioning and individual quality of life for parents living with HIV. In particular, family sociability had a strong relationship with the quality of life of parents living with HIV. Parents living with HIV from families where both parents are HIV-positive reported a lower level of family sociability than those from families with only one HIV-positive parent. HIV disclosure, family sociability, and number of children per family were found to be significant predictors of overall quality of life for the population. Study findings underscore the importance of developing interventions that improve family functioning for people living with HIV/AIDS in China.

Intact Adelta-fibers up-regulate transient receptor potential A1 and contribute to cold hypersensitivity in neuropathic rats

Mechanisms underlying cold hypersensitivity in neuropathic states are unclear. Recent data indicate both transient receptor potential (TRP) M8 and TRPA1 play a role. In relation to TRPA1, there are reported increases in mRNA. However, it is unknown whether TRPA1 mRNA is translated into functional receptors, whether these receptors are found on peripheral nociceptors and what population of primary afferents expresses the receptors. The present study provides several lines of evidence that TRPA1 receptors are expressed on intact primary sensory neurons and contribute to cold hypersensitivity following spinal nerve ligation (SNL). Immunohistochemical studies show that expression of TRPA1 is significantly increased in the ipsilateral compared with the contralateral L4 dorsal root ganglion (DRG). Using mustard oil (MO, selective TRPA1 agonist), Ca(2+) imaging demonstrates an increase in the percentage of MO-sensitive L4 DRG cells in SNL compared with sham and naive rats. The magnitude of the Ca(2+) response evoked by MO is also significantly larger in SNL compared with sham and naive rats. Behavioral studies demonstrate that SNL results in increased nocifensive behaviors to mechanical and cold stimulation that is not seen in sham or naive rats. Behavioral responses in sham rats are no different from naive rats. In vitro single fiber recordings demonstrate Adelta-fibers (intact L4 axons) in the nerve-injured hind paw have conduction velocities no different from naive rats. In contrast, compared with naive rats, mechanical thresholds of the Adelta-fibers in SNL rats are significantly decreased, the proportion of cold-sensitive and MO-sensitive Adelta-fibers is significantly increased and the response magnitude of Adelta-fibers to MO is significantly increased. MO-induced activity in Adelta-fibers is significantly reduced by Ruthenium Red (TRPA1 receptor antagonist). These results demonstrate that TRPA1 is expressed on peripheral nociceptors, and they are up-regulated on intact Adelta-fibers following nerve injury, contributing to cold hypersensitivity.

Plasticity in intact A delta- and C-fibers contributes to cold hypersensitivity in neuropathic rats

Cold hypersensitivity is a common sensory abnormality accompanying peripheral neuropathies and is difficult to treat. Progress has been made in understanding peripheral mechanisms underlying neuropathic pain but little is known concerning peripheral mechanisms of cold hypersensitivity. The aim of this study was to analyze the contribution of uninjured primary afferents to the cold hypersensitivity that develops in neuropathic rats. Rats with a lumbar 5 (L5) and L6 spinal nerve ligation (SNL, Chung model) but not sham, developed mechanical allodynia, evidenced by decreased paw withdrawal thresholds and increased magnitude of response to von Frey stimulation. Cold hypersensitivity also developed in SNL but not sham rats, evidenced by enhanced nociceptive behaviors induced by placement on a cold plate (6 degrees C) or application of icilin (a transient receptor potential M8 (TRPM8)/transient receptor potential A1 (TRPA1) receptor agonist) to nerve-injured hind paws. Single fiber recordings demonstrated that the mean conduction velocities of intact L4 cutaneous A delta- and C-fibers were not different between naive and SNL rats; however, mechanical thresholds of the A delta- but not the C-fibers were significantly decreased in SNL compared with naive. There was a higher prevalence of C-mechanoheat-cold (CMHC) fibers in SNL compared with naive, but the overall percentage of cold-sensitive C-fibers was not significantly increased compared with naive. This was in contrast to the numerous changes in A delta-fibers: the percentage of L4 cold sensitive A delta-, but not C-fibers, was significantly increased, the percentage of L4 icilin-sensitive A delta-, but not C-fibers, was significantly increased, the icilin-induced activity of L4 A delta-, but not C-fibers, was significantly increased. Icilin-induced activity was blocked by the TRPA1 antagonist Ruthenium Red. The results indicate plasticity in both A delta- and C-uninjured fibers, but A delta fibers appear to provide a major contribution to cold hypersensitivity in neuropathic rats.

First Report of Aloe Root and Stem Rot in China Caused by Fusarium solani

During the springs of 2003 and 2004, a serious outbreak of root and stem disease occurred on Aloe barbadensis L. grown in commercial fields in Yuanjiang, Yunnan Province, Southwest China. The disease began with brown root rots that advanced to collars and stems, followed by internal decay of the lower stem. Diseased tissue samples collected from plants in different fields were surface disinfested and plated on potato dextrose agar (PDA). A Fusarium species was consistently isolated, and pure cultures were established by initiating new cultures with single spores. Grayish white and fluffy mycelium with a deep violet-blue pigment developed on PDA agar, with a growth rate of 3.4 cm in 3 days, and a dark, blue-green mass of confluent sporodochia or pionnotes covering the central part of the culture. Microconidia in false heads on long phialides were abundant when initially isolated but were infrequent in later cultures. Microconidia were generally single celled, oval to kidney shaped, and 8 to 16 × 2.5 to 4 μm. Macroconidia were abundant, cylindrical, slightly curved with blunt and rounded apical cells, and foot-shaped or notched basal cells, and mostly three to four septate, 27 to 50 × 3.6 to 5.7 μm. Chlamydospores were sparse, single or in short chains, thick walled, and 7 to 10 μm in diameter. This description corresponds to Fusarium solani (Mart.) Appel & Wollenw. emend. Snyd. & Hans as described by Nelson et al. (1). Inoculations with F. solani were made by dipping healthy aloe roots into a 300-ml suspension of 3 × 10⁵ conidia/ml. Control plants were dipped in sterile water. All plants were potted in soil and kept in a greenhouse (2). After 30 days, all inoculated plants developed root rots followed by collar and stem rots that were similar to those observed in the field. Cultures of F. solani were reisolated from the diseased plants and identification was confirmed by conidial characteristics. No symptoms were observed on the control plants. Tests were repeated with similar results. In China, the Yunnan Province produces one-third of all aloe grown and this disease has a major impact on production. Aloe is grown in certified organic fields and chemical pesticides are not used. To our knowledge, this is the first report of F. solani causing root and stem rot of A. barbadensis. References: (1) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, PA, 1983. (2) X. Ruan et al. Pages 211-215 in: Phytopathology Laboratory of Yunnan Province. Vol. 2. Y. Y. Shengfu, ed. Yunnan Science and Technology Press, Kunming, Yunnan, China, 1998.

Prevalence of and risk factors for non-compliance with glove utilization and hand hygiene among obstetrics and gynaecology workers in rural China

This study identified the prevalence of and risk factors for non-compliance with glove utilization and hand hygiene among rural obstetrics and gynaecology workers in two poor counties in Anhui, China. A cross-sectional survey was conducted using a self-administered anonymous semi-structured questionnaire. The study population included all health workers in the departments of obstetrics and gynaecology in township hospitals and county health facilities. Among the 137 participants, the rate of non-compliance with glove utilization was 61%, the rate of non-compliance with hand hygiene was 40%, and the rate of non-compliance with both was 67%. 'Unnecessary and inconvenient' accounted for 66% of the reasons for not always using gloves and 71% for not always washing hands. 'Short of gloves or water' accounted for 15% and 22% of reasons, respectively. Two variables were associated with non-compliance: county [odds ratio (OR)=11.56, P<0.001] and knowledge (OR=0.10, P=0.033). After removing county from the regression model, institutional level (OR=2.34, P=0.059), institutional support (OR=3.85, P=0.009) and knowledge (OR=0.05, P=0.007) were associated with non-compliance. The prevalence of non-compliance with glove utilization and hand hygiene was high. The risk factors for non-compliance were institutional level, institutional support and knowledge. These variables incorporated both subjective and objective reasons for non-compliance.

von Willebrand factor binding to platelet glycoprotein Ib-IX-V stimulates the assembly of an alpha-actinin-based signaling complex

BACKGROUND

Pathological shear stress induces platelet aggregation that is dependent on von Willebrand factor (VWF) binding to glycoprotein (Gp)Ib-IX-V and phosphatidylinositol 3-kinase activation. We tested the hypothesis that pathological shear stress stimulates phosphatidylinositol 3,4,5-trisphosphate (PIP3) synthesis by directing the assembly of a molecular signaling complex that includes class IA phosphatidylinositol 3-kinase (PI 3-KIA).

METHODS

Platelets were subjected to 120 dynes cm-2 shear stress in a cone-plate viscometer. Resting and sheared platelets were lyzed, immunoprecipitations of PI 3-KIA performed, or lipids extracted for PIP3 measurements. alpha-Actinin was incubated with phosphatidylinositol 4,5-bisphosphate (PIP2), immunoprecipitated, and used as a substrate for in vitro PI 3-KIA activity.

RESULTS

Pathological shear stress induces biphasic PIP3 production. In resting platelets, PI 3-KIA associates with alpha-actinin and PIP2. After exposure to shear stress, alpha-actinin and PIP2 rapidly disassociate from PI 3-KIA. PI 3-KIA then gradually re-associates with PIP2 and alpha-actinin, and this complex becomes linked to GpIb alpha through the cytoskeleton. PIP3 production and the observed changes in the association between alpha-actinin, PIP2, and PI 3-KIA are inhibited when VWF binding to GpIb alpha is blocked. In a cell-free system, alpha-actinin binds PIP2 and when the alpha-actinin-PIP2 complex is added to platelet PI 3-KIA, PIP3 production is stimulated.

CONCLUSIONS

These results suggest that pathological shear-induced VWF binding to GpIb-IX-V stimulates PIP3 production through the assembly of an alpha-actinin-based complex that colocalizes PI 3-KIA with substrate PIP2.

Smooth muscle expression of Cre recombinase and eGFP in transgenic mice

We report the generation of transgenic mice designed to facilitate the study of vascular and nonvascular smooth muscle biology in vivo. The smooth muscle myosin heavy chain (smMHC) promoter was used to direct expression of a bicistronic transgene consisting of Cre recombinase and enhanced green fluorescent protein (eGFP) coding sequences. Animals expressing the transgene display strong fluorescence confined to vascular and nonvascular smooth muscle. Enzymatic dissociation of smooth muscle yields viable, fluorescent cells that can be studied as single cells or sorted by FACS for gene expression studies. smMHC/Cre/eGFP mice were crossed with ROSA26/lacZ reporter mice to determine Cre recombinase activity; Cre recombinase was expressed in all smooth muscles in adult mice, and there was an excellent overlap between expression of the recombinase and eGFP. Initial smooth muscle-specific expression of fluorescence and Cre recombinase was detected on embryonic day 12.5. These mice will be useful to define smooth muscle gene function in vivo in mice, for the study of gene function in single, live cells, and for the determination of gene expression in vascular and nonvascular smooth muscle.

Disruption of cytoskeletal integrity impairs Gi-mediated signaling due to displacement of Gi proteins

beta1 integrins play a crucial role as cytoskeletal anchorage proteins. In this study, the coupling of the cytoskeleton and intracellular signaling pathways was investigated in beta1 integrin deficient (-/-) embryonic stem cells. Muscarinic inhibition of the L-type Ca2+ current (ICa) and activation of the acetylcholine-activated K+ current (IK,ACh) was found to be absent in beta1 integrin-/- cardiomyocytes. Conversely, beta adrenoceptor-mediated modulation of ICa was unaffected by the absence of beta1 integrins. This defect in muscarinic signaling was due to defective G protein coupling. This was supported by deconvolution microscopy, which demonstrated that Gi exhibited an atypical subcellular distribution in the beta1 integrin-/- cardiomyocytes. A critical role of the cytoskeleton was further demonstrated using cytochalasin D, which displaced Gi and impaired muscarinic signaling. We conclude that cytoskeletal integrity is required for correct localization and function of Gi-associated signaling microdomains.

[Super heavy oil produced water treatment by surface flow constructed wetland]

This paper adopts a new economic technology of treating super heavy oil produced water using surface flow reed wetland system. The field test was conducted at the average filtration rate of 3.33 cm/d. The average influent concentrations per year of COD, Oil, BOD5, TN were 459.16 mg/L, 27.65 mg/L, 33.52 mg/L, 13.74 mg/L, and the average effluent concentrations per year of above indices were 77.21 mg/L, 1.42 mg/L, 3.90 mg/L, 1.60 mg/L, respectively. Its respective removal ratios of COD, Oil, BOD5, TN and pH were 83.18%, 94.86%, 88.37%, 88.36%, 7.87-7.77. Analyses showed that super heavy oil produced water had no obvious effect on soil and almost no effect on growth volume and quality of reeds. Results indicated that the surface flow reed wetland could provide an efficient economical, stable new means of treating super heavy oil produced water.

[Kinetics of interaction of H+ with constant and variable charge soils]

The kinetics of interaction of H+ ions with constant and variable charge soils were studied, among which changes of H+ concentration, positive surface charge and soluble Al with time and their influencing factors were investigated in detail. The results showed that the consumption processes of H+ ions in both constant and variable charge soils could be divided into fast and slow processes, but the manifestations and influencing factors were different for the two types of soils. The variations in positive surface charges for variable and constant charge soils, due to the difference in the contents of free Fe-oxides, are remarkably different and thus can not be modeled mathematically in the same manner for the two types of soils. The variations in soluble Al for both variable and constant charge soils were controlled by the components, solubility and solution kinetics of dominant clay minerals in soils, and could be described by both modified Elovich and two-constant rate equations mathematically.

Characterization of high molecular weight cadmium species in contaminated vegetable food

Spinach and radish grown from seeds were each contaminated with 4 different amounts of cadmium. After a cell breakdown of the eatable parts and centrifugation of the resulting homogenates all supernatants (cytosols) were separated by gel permeation chromatography (GPC). The size-range of the GPC method used was about 20-8000 kDa for globular proteins. The high molecular weight (HMW-Cd-SP, 150-700 kDa) and the low molecular weight Cd species (LMW-Cd-SP, < 150 kDa) in all plant cytosols eluted at about the same retention volume by GPC. The most important Cd binding form in the cytosols of all plants was found to be HMW-Cd-SP. The Cd elution maxima were detected in the range of about 200 kDa. The Cd determinations were performed with ET-AAS by means of matrix modifier. By incubating chosen cytosols with a proteinase before the GPC it was verified that the HMW-Cd-SP in both vegetables are Cd proteins. The molar proportions protein/Cd were about 2-6 in the respective GPC fractions of the HMW-Cd-SP of the highest contaminated plants. The GPC fractions of the HMW-Cd-SP of spinach and radish were further separated by a preparative, native and continuous polyacrylamide gel electrophoresis (PAGE) method. At pH 8 the species were negatively charged, had only a small UV-absorption at 280 nm and showed a very similar elution behavior in all analyzed cytosols. Therefore, we suppose that the HMW-Cd-SP of these two different vegetable foodstuffs have a very similar chemical structure.

X-chromosome inactivation in the human trophoblast of early pregnancy

To investigate X-chromosome inactivation (XCI) in human trophoblasts during early pregnancy, trophoblast genomic DNA was extracted and analyzed for a Bst XI restriction endonuclease site polymorphism in the X-linked phosphoglycerate kinase gene, after digestion with methylation-sensitive Hpa II (control samples were digested instead with Afa I). Six villous trophoblast DNA samples were informative for the polymorphism (ie, heterozygous) and were derived from women homozygous for the polymorphism. These samples were then evaluated for XCI. In five of the six samples with Hpa II predigestion, the sizes of the two heterozygous band peaks differed; maternal X-chromosome (X(M))-derived alleles showed smaller peak sizes than paternal X-chromosome (X(P))-derived alleles, but the differences varied in degree. In samples obtained by microdissection from formalin-fixed, paraffin-embedded tissues (30 samples from different anchoring villi, and 38 samples from different branch villi), monoclonal band patterns of X(P)-derived alleles were observed more frequently than those of X(M)-derived alleles, but almost half of the samples showed polyclonal patterns. Our results suggest that a skewing of XCI exists in the human trophoblast; however, the degree of nonrandomness due to predominant X(P) inactivation appears to be restricted. It is probable that transcription of the X inactivation center (XIC) begins earlier in mice than in humans.

Calcium-induced calcium release in smooth muscle: loose coupling between the action potential and calcium release

Calcium-induced calcium release (CICR) has been observed in cardiac myocytes as elementary calcium release events (calcium sparks) associated with the opening of L-type Ca(2+) channels. In heart cells, a tight coupling between the gating of single L-type Ca(2+) channels and ryanodine receptors (RYRs) underlies calcium release. Here we demonstrate that L-type Ca(2+) channels activate RYRs to produce CICR in smooth muscle cells in the form of Ca(2+) sparks and propagated Ca(2+) waves. However, unlike CICR in cardiac muscle, RYR channel opening is not tightly linked to the gating of L-type Ca(2+) channels. L-type Ca(2+) channels can open without triggering Ca(2+) sparks and triggered Ca(2+) sparks are often observed after channel closure. CICR is a function of the net flux of Ca(2+) ions into the cytosol, rather than the single channel amplitude of L-type Ca(2+) channels. Moreover, unlike CICR in striated muscle, calcium release is completely eliminated by cytosolic calcium buffering. Thus, L-type Ca(2+) channels are loosely coupled to RYR through an increase in global [Ca(2+)] due to an increase in the effective distance between L-type Ca(2+) channels and RYR, resulting in an uncoupling of the obligate relationship that exists in striated muscle between the action potential and calcium release.

[Relation of GFR and endothelin in the plasma in pilots and ground crew]

OBJECTIVE

To observe the specitic property of Glomeoular Filtration Rate (GFR) and its relation to endothelin of plasma in pilots.

METHOD

GFR was assessed with single photon emisson computed tomography (SPECT), tracer for 99mTc-DTPA, enthlion of plasma were measured by radio immunossay in forty-six pilots, thirty ground crew and renal disease patients.

RESULT

Endothelin were not correlation with GFR in pilots. GFR of pilots and ground crew had not a significant difference. Compared with ground crew and pilots, endothelin of renal disease patients had a significant increased, and GFR had a significant decreased. Age were a linear negative correlation with total GFR r = (0.84, P < 0.01), flying time, age had not correlation with endothelin. After thirty-one ground endothelin had a significant difference with ground crew.

CONCLUSION

It suggested that the endothelin has no influence on GFR in pilots when it was increased with in the limits of a level, pilots and ground crew may use the same stand on GFR.

Establishment of ionic channels and signalling cascades in the embryonic stem cell-derived primitive endoderm and cardiovascular system

The first organ system to be established in early embryogenesis is the cardiovascular system which develops upon interaction with hypoblastic cells of the primitive endoderm. Here we focus on recent work on embryoid bodies derived from pluripotent embryonic stem (ES) cells. Ca(2+) oscillations and Ca(2+) signalling pathways during the differentiation of primitive endodermal cell layers are reported. Furthermore, the development-dependent expression of ion channels and the buildup of signalling cascades involved in the modulation of voltage-dependent L-type Ca(2+) channels during early cardiomyogenesis and the formation of functional vascular structures in the process of vasculogenesis and angiogenesis are reviewed. We also report on the use of green fluorescent protein reporter gene expression under the control of cardiac-specific promoters, e.g. the human cardiac alpha-actin promoter, which enables the identification and in vivo characterization of cardiomyocytes at very early stages of cardiomyogenesis.

Molecular chain orientation in supercontracted and re-extended spider silk

The dragline silk from Nephila clavipes was studied by wide angle X-ray diffraction in its original state, after supercontraction to L/Lo = 0.46, and during re-extension to its original length Lo. The fibers were carefully dried before each exposure. The molecular orientation in the crystalline regions is found to follow the simple predictions of affine deformation, indicating that the crystals act as inert rigid filler particles. The crystals retain considerable orientation after supercontraction, when non-crystalline orientation is weak. This shows that crystallization occurs after orientation as the fiber forms. The oriented amorphous material, treated as a phase of constant volume fraction, also follows affine deformation. These results do not contain any indication of a special structure in the protein fiber.

Structure-activity analysis of synthetic autoinducing thiolactone peptides from Staphylococcus aureus responsible for virulence

The synthesis of virulence factors and other extracellular proteins responsible for pathogenicity in Staphylococcus aureus is under the control of the agr locus. A secreted agr-encoded peptide, AgrD, processed from the AgrD gene product, is known to be an effector of self-strain activation and cross-strain inhibition of the agr response. Biochemical analysis of AgrD peptides isolated from culture supernatants has suggested that they contain an unusual thiol ester-linked cyclic structure. In the present work, chemical synthesis is used to confirm that the mature AgrD peptides contain a thiolactone structure and that this feature is absolutely necessary for full biological activity. The AgrD synthetic thiolactone peptides exhibited biological activity in vivo in a mouse protection test. Structure-activity studies have allowed key aspects of the peptide structure involved in the differential activation and inhibition functions to be identified. Accordingly, we propose a model for activation and inhibition of the agr response in which the former, but not the latter, involves specific acylation of the agr transmembrane receptor, AgrC.