Identification of key mutations responsible for the enhancement of receptor-binding affinity and immune escape of SARS-CoV-2 Omicron variant.

The Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has raised concerns worldwide due to its enhanced transmissibility and immune escapability. The first dominant Omicron BA.1 subvariant harbors more than 30 mutations in the spike protein from the prototype virus, of which 15 mutations are located at the receptor binding domain (RBD). These mutations in the RBD region attracted significant attention, which potentially enhance the binding of the receptor human angiotensin-converting enzyme 2 (hACE2) and decrease the potency of neutralizing antibodies/nanobodies. This study applied the molecular dynamics simulations combined with the molecular mechanics-generalized Born surface area (MMGBSA) method, to investigate the molecular mechanism behind the impact of the mutations acquired by Omicron on the binding affinity between RBD and hACE2. Our results indicate that five key mutations, i.e., N440K, T478K, E484A, Q493R, and G496S, contributed significantly to the enhancement of the binding affinity by increasing the electrostatic interactions of the RBD-hACE2 complex. Moreover, fourteen neutralizing antibodies/nanobodies complexed with RBD were used to explore the effects of the mutations in Omicron RBD on their binding affinities. The calculation results indicate that the key mutations E484A and Y505H reduce the binding affinities to RBD for most of the studied neutralizing antibodies/nanobodies, mainly attributed to the elimination of the original favorable gas-phase electrostatic and hydrophobic interactions between them, respectively. Our results provide valuable information for developing effective vaccines and antibody/nanobody drugs.

Identification of the Intrinsic Motions and Related Key Residues Responsible for the Twofold Channel Opening of Poliovirus Capsid by Using an Elastic Network Model Combined with an Internal Coordinate.

Poliovirus (PV) is an infectious virus that causes poliomyelitis, which seriously threatens the health of children. The release of viral RNA is a key step of PV in host cell infection, and multiple lines of evidence have demonstrated that RNA release is initiated by the opening of the twofold channels of the PV capsid. However, the mechanism that controls the twofold channel opening is still not well understood. In addition, the channel opening motion of the recombinant PV capsid leads to the destruction of predominant neutralizing epitopes and thus hinders the capsid as a vaccine immunogen. Therefore, it is important to identify the intrinsic motions and the related key residues controlling the twofold channel opening for understanding the virus infection mechanism and developing capsid-based vaccines. In the present work, the width of the channel was selected as an internal coordinate directly related to the channel opening, and then the elastic network model (ENM) combined with the group theory were employed to extract the intrinsic motion modes that mostly contribute to the opening of the twofold channels. Our results show that the channel opening predominately induced by the breathing motion and the overall rotation of each protomer in the capsid. Then, an internal coordinate-based perturbation method was used to identify the key residues regulating the twofold channel opening of PV. The calculation results showed that the predicted key residues are mainly located at the twofold axes, the bottom of the canyons and the quasi threefold axes. Our study is helpful for better understanding the twofold channel opening mechanism and provides a potential target for preventing the opening of the channels, which is of great significance for PV vaccine design. The source code of this study is available at https://github.com/SJGLAB/CapsidKeyRes.git.

Research progress of cyclic peptide synthesis strategy and its application in new drug development / 药学学报

Protein-protein interaction (PPI) plays an important role in the regulation of life. Most of the PPI interfaces are large and discontinuous, and it is difficult for small molecules to specifically bind to them. Peptides are critical in PPI surface interactions due to their higher affinity and specificity. However, peptides have some defects such as easy hydrolysis by protease and poor membrane permeability. Due to good biocompatibility and chemical diversity, cyclic peptides play an important role in drug discovery. Therefore, the development of efficient cyclic peptide construction methods has become a frontier issue in peptide drug research. In recent years, a series of new progresses have been made in the synthesis strategy and the application of cyclic peptides, providing powerful technical tools for the research and development of cyclic peptide drugs. In this review, the synthesis strategies of cyclic peptides and their application will be reviewed from four aspects: synthesis strategies, property improvement, biological activity and prospect.

Omega-3 fatty acids impair miR-1-3p-dependent Notch3 down-regulation and alleviate sepsis-induced intestinal injury.

BACKGROUND: Sepsis is a troublesome syndrome that can cause intestinal injury and even high mortality rates. Omega-3 fatty acids (FAs) are known to protect against intestinal damage. Accordingly, the current study set out to explore if omega-3 FAs could affect sepsis-induced intestinal injury with the involvement of the microRNA (miR)-1-3p/Notch3-Smad axis. METHODS: First, cecal ligation and perforation (CLP) was performed to establish septic mouse models in C57BL/6J mice, and mouse intestinal epithelial MODE-K cells were induced by lipopolysaccharide (LPS) to establish sepsis cell models. The CLP-induced septic mice or LPS-exposed cells were subjected to treatment with Omega-3 FAs and activin (Smad signaling activator), miR-1-3p inhibitor and over-expressed/short hairpin RNA (oe-/sh)-Notch3 to explore their roles in inflammation, intestinal oxidative stress and cell apoptosis. A dual-luciferase reporter gene assay was further performed to verify the regulatory relationship between miR-1-3p and Notch3. RESULTS: Omega-3 FAs inhibited CLP-induced intestinal injury and ameliorated LPS-induced intestinal epithelial cell injury by down-regulating miR-1-3p, as evidenced by decreased levels of tumor necrosis factor-α, interleukin-1ß (IL-1ß) and IL-6, in addition to diminished levels of reactive oxygen species, malondialdehyde levels and superoxide dismutase activity. Furthermore, miR-1-3p could down-regulate Notch3, which inactivated the Smad pathway. CONCLUSION: Collectively, our findings indicated that omega-3 FAs elevate the expression of Notch3 by down-regulating miR-1-3p, and then blocking the Smad pathway to alleviate intestinal epithelial inflammation and oxidative stress injury caused by sepsis.

E484K mutation in SARS-CoV-2 RBD enhances binding affinity with hACE2 but reduces interactions with neutralizing antibodies and nanobodies: Binding free energy calculation studies.

The pandemic of the COVID-19 disease caused by SARS-CoV-2 has led to more than 200 million infections and over 4 million deaths worldwide. The progress in the developments of effective vaccines and neutralizing antibody therapeutics brings hopes to eliminate the threat of COVID-19. However, SARS-CoV-2 continues to mutate, and several new variants have been emerged. Among the various naturally-occurring mutations, the E484K mutation shared by many variants attracted serious concerns, which may potentially enhance the receptor binding affinity and reduce the immune response. In the present study, the molecular mechanism behind the impacts of E484K mutation on the binding affinity of the receptor-binding domain (RBD) with the receptor human angiotensin-converting enzyme 2 (hACE2) was investigated by using the molecular dynamics (MD) simulations combined with the molecular mechanics-generalized Born surface area (MMGBSA) method. Our results indicate that the E484K mutation results in more favorable electrostatic interactions compensating the burial of the charged and polar groups upon the binding of RBD with hACE2, which significantly improves the RBD-hACE2 binding affinity. Besides that, the E484K mutation also causes the conformational rearrangements of the loop region containing the mutant residue, which leads to tighter binding interface of RBD with hACE2 and formation of some new hydrogen bonds. The tighter binding interface and the new hydrogen bonds formation also contribute to the improved binding affinity of RBD to the receptor hACE2. In addition, six neutralizing antibodies and nanobodies complexed with RBD were selected to explore the effects of E484K mutation on the recognition of these antibodies to RBD. The simulation results show that the E484K mutation significantly reduces the binding affinities to RBD for most of the studied neutralizing antibodies/nanobodies, and the decrease in the binding affinities is mainly owing to the unfavorable electrostatic interactions caused by the mutation. Our studies revealed that the E484K mutation may improve the binding affinity between RBD and the receptor hACE2, implying more transmissibility of the E484K-containing variants, and weaken the binding affinities between RBD and the studied neutralizing antibodies/nanobodies, indicating reduced effectiveness of these antibodies/nanobodies. Our results provide valuable information for the effective vaccine development and antibody/nanobody drug design.

Evolution of the interactions between GII.4 noroviruses and histo-blood group antigens: Insights from experimental and computational studies.

Norovirus (NoV) is the major pathogen causing the outbreaks of the viral gastroenteritis across the world. Among the various genotypes of NoV, GII.4 is the most predominant over the past decades. GII.4 NoVs interact with the histo-blood group antigens (HBGAs) to invade the host cell, and it is believed that the receptor HBGAs may play important roles in selecting the predominate variants by the nature during the evolution of GII.4 NoVs. However, the evolution-induced changes in the HBGA-binding affinity for the GII.4 NoV variants and the mechanism behind the evolution of the NoV-HBGA interactions remain elusive. In the present work, the virus-like particles (VLPs) of the representative GII.4 NoV stains epidemic in the past decades were expressed by using the Hansenula polymorpha yeast expression platform constructed by our laboratory, and then the enzyme linked immunosorbent assay (ELISA)-based HBGA-binding assays as well as the molecular dynamics (MD) simulations combined with the molecular mechanics/generalized born surface area (MMGBSA) calculations were performed to investigate the interactions between various GII.4 strains and different types of HBGAs. The HBGA-binding assays show that for all the studied types of HBGAs, the evolution of GII.4 NoVs results in the increased NoV-HBGA binding affinities, where the early epidemic strains have the lower binding activity and the newly epidemic strains exhibit relative stronger binding intensity. Based on the MD simulation and MMGBSA calculation results, a physical mechanism that accounts for the increased HBGA-binding affinity was proposed. The evolution-involved residue mutations cause the conformational rearrangements of loop-2 (residues 390-396), which result in the narrowing of the receptor-binding pocket and thus tighten the binding of the receptor HBGAs. Our experimental and computational studies are helpful for better understanding the mechanism behind the evolution-induced increasing of HBGA-binding affinity, which may provide useful information for the drug and vaccine designs against GII.4 NoVs.

E484K mutation in SARS-CoV-2 RBD enhances binding affinity with hACE2 but reduces interactions with neutralizing antibodies and nanobodies: Binding free energy calculation studies

The pandemic of the COVID-19 disease caused by SARS-CoV-2 has led to more than 100 million infections and over 2 million deaths worldwide. The progress in the developments of effective vaccines and neutralizing antibody therapeutics brings hopes to eliminate the threat of COVID-19. However, SARS-CoV-2 continues to mutate, and several new variants have been emerged. Among the various naturally-occurring mutations, the E484K mutation shared by both the 501Y.V2 and 501Y.V3 variants attracted serious concerns, which may potentially enhance the receptor binding affinity and reduce the immune response. In the present study, the molecular mechanism behind the impacts of E484K mutation on the binding affinity of the receptor-binding domain (RBD) with the receptor human angiotensin-converting enzyme 2 (hACE2) was investigated by using the molecular dynamics (MD) simulations combined with the molecular mechanics-generalized Born surface area (MMGBSA) method. Our results indicate that the E484K mutation results in more favorable electrostatic interactions compensating the burial of the charged and polar groups upon the binding of RBD with hACE2, which significantly improves the RBD-hACE2 binding affinity. Besides that, the E484K mutation also causes the conformational rearrangements of the loop region containing the mutant residue, which leads to more tight binding interface of RBD with hACE2 and formation of some new hydrogen bonds. The more tight binding interface and the new hydrogen bonds formation also contribute to the improved binding affinity of RBD to the receptor hACE2. In addition, six neutralizing antibodies and nanobodies complexed with RBD were selected to explore the effects of E484K mutation on the recognition of these antibodies to RBD. The simulation results show that the E484K mutation significantly reduces the binding affinities to RBD for most of the studied neutralizing antibodies, and the decrease in the binding affinities is mainly owing to the unfavorable electrostatic interactions caused by the mutation. Our studies revealed that the E484K mutation may improve the binding affinity between RBD and the receptor hACE2, implying more transmissibility of the E484K-containing variants, and weaken the binding affinities between RBD and the studied neutralizing antibodies, indicating reduced effectiveness of these antibodies. Our results provide valuable information for the effective vaccine development and antibody drugs design.

Enhancement of protein mechanical stability: Correlated deformations are handcuffed by ligand binding.

As revealed by previous experiments, protein mechanical stability can be effectively regulated by ligand binding with the binding site distant from the force-bearing region. However, the mechanism for such long-range allosteric control of protein mechanics is still largely unknown. In this work, we use protein topology-based elastic network model (ENM) and all-atomic steered molecular dynamics (SMD) simulations to study the impact of ligand binding on protein mechanical stability in two systems, i.e., GB1 and CheY-binding P2-domain of CheA (CBDCheA). Both ENM and SMD results show that the ligand binding has considerable and negligible effects on the mechanical stability of these two proteins, respectively. These results are consistent with the experimental observations. A physical mechanism for the enhancement of protein mechanical stability was then proposed: the correlated deformations of the force-bearing region and the binding site are handcuffed by the binding of ligand. The handcuff effect suppresses the propagation of internal force in the force-bearing region, thus improving the resistance to the loading force. Our study indicates that ENM method can effectively identify the structure motifs allosterically related to the deformation in the force bearing region, as well as the force propagation pathway within the structure of the studied proteins. Hence, it should be helpful to understand the molecular origin of the different mechanical properties in response to ligand binding for GB1 and CBDCheA.

Effects of Polygonum cuspidatum on AMPK-FOXO3α Signaling Pathway in Rat Model of Uric Acid-Induced Renal Damage / 中国结合医学杂志

BACKGROUND@#To observe the effects of Chinese medicine (CM) Polygonum cuspidatum (PC) on adenosine 5'-monophosphate-activated protein kinase (AMPK), forkhead box O3α (FOXO3α), Toll-like receptor-4 (TLR4), NACHT, LRR and PYD domains-containing protein 3 (NLRP3), and monocyte chemoattractant protein-1 (MCP-1) expression in a rat model of uric acid-induced renal damage and to determine the molecular mechanism.@*METHODS@#A rat model of uric acid-induced renal damage was established, and rats were randomly divided into a model group, a positive drug group, and high-, medium-, and low-dose PC groups (n=12 per group). A normal group (n=6) was used as the control. Rats in the normal and model groups were administered distilled water (10 mL•kg) by intragastric infusion. Rats in the positive drug group and the high-, medium-, and low-dose PC groups were administered allopurinol (23.33 mg•kg), and 7.46, 3.73, or 1.87 g•kg•d PC by intragastric infusion, respectively for 6 to 8 weeks. After the intervention, reverse transcription polymerase chain reaction, Western blot, enzyme linked immunosorbent assay, and immunohistochemistry were used to detect AMPK, FOXO3α, TLR4, NLRP3, and MCP-1 mRNA and protein levels in renal tissue or serum.@*RESULTS@#Compared with the normal group, the mRNA transcription levels of AMPK and FOXO3α in the model group were significantly down-regulated, and protein levels of AMPKα1, pAMPKα1 and FOXO3α were significantly down-regulated at the 6th and 8th weeks (P<0.01 or P<0.05). The mRNA transcription and protein levels of TLR4, NLRP3 and MCP-1 were significantly up-regulated (P<0.01 or P<0.05). Compared with the model group, at the 6th week, the mRNA transcription levels of AMPK in the high- and medium-dose groups, and protein expression levels of AMPKα1, pAMPKα1 and FOXO3α in the high-dose PC group, AMPKα1 and pAMPKα1 in the mediumdose PC group, and pAMPKα1 in the low-dose PC group were significantly up-regulated (P<0.01 or P<0.05); the mRNA transcription and protein levels of TLR4 and NLRP3 in the 3 CM groups, and protein expression levels of MCP-1 in the medium- and low-dose PC groups were down-regulated (P<0.01 or P<0.05). At the 8th week, the mRNA transcription levels of AMPK in the high-dose PC group and FOXO3α in the medium-dose PC group, and protein levels of AMPKα1, pAMPKα1 and FOXO3α in the 3 CM groups were significantly up-regulated (P<0.01 or P<0.05); the mRNA transcription levels of TLR4 in the medium- and low-dose PC groups, NLRP3 in the high- and low-dose PC groups and MCP-1 in the medium- and low-dose PC groups, and protein expression levels of TLR4, NLRP3 and MCP-1 in the 3 CM groups were down-regulated (P<0.01 or P<0.05).@*CONCLUSION@#PC up-regulated the expression of AMPK and its downstream molecule FOXO3α and inhibited the biological activity of TLR4, NLRP3, and MCP-1, key signal molecules in the immunoinflammatory network pathway, which may be the molecular mechanism of PC to improve hyperuricemia-mediated immunoinflflammatory metabolic renal damage.

Energy transport pathway in proteins: Insights from non-equilibrium molecular dynamics with elastic network model.

Intra-molecular energy transport between distant functional sites plays important roles in allosterically regulating the biochemical activity of proteins. How to identify the specific intra-molecular signaling pathway from protein tertiary structure remains a challenging problem. In the present work, a non-equilibrium dynamics method based on the elastic network model (ENM) was proposed to simulate the energy propagation process and identify the specific signaling pathways within proteins. In this method, a given residue was perturbed and the propagation of energy was simulated by non-equilibrium dynamics in the normal modes space of ENM. After that, the simulation results were transformed from the normal modes space to the Cartesian coordinate space to identify the intra-protein energy transduction pathways. The proposed method was applied to myosin and the third PDZ domain (PDZ3) of PSD-95 as case studies. For myosin, two signaling pathways were identified, which mediate the energy transductions form the nucleotide binding site to the 50 kDa cleft and the converter subdomain, respectively. For PDZ3, one specific signaling pathway was identified, through which the intra-protein energy was transduced from ligand binding site to the distant opposite side of the protein. It is also found that comparing with the commonly used cross-correlation analysis method, the proposed method can identify the anisotropic energy transduction pathways more effectively.

Balancing Effect of Biejiajian Oral Liquid () on ACE-Ang II-AT1R Axis and ACE2-Ang-(1-7)-Mas Axis in Rats with CCl-Induced Hepatic Fibrosis / 中国结合医学杂志

<p><b>OBJECTIVE</b>To explore the effect of Biejiajian Oral Liquid (, BOL) on CCl-induced hepatic fibrosis in rats by detecting the changes in the levels of angiotensin II (Ang II), angiotensin-(1-7) [Ang-(1-7)], angiotensin-converting enzyme (ACE), ACE2, angiotensin II type 1 receptor (AT1R), Mas, etc. METHODS: A total of 180 Wistar rats were randomly divided into two groups by random digital table method: prevention experiment and treatment experiment. Each group was further subdivided into the following 6 subgroups: normal control group, model group, vitamin E [100 mg/(kg·d), VE] group, enalapril [10 mg/(kg·g), Ena] group, high-dosage [20 g/(kg·d)] BOL group, and low-dosage [10 g/(kg·d)] BOL group. The hepatic fibrosis rat model was established by subcutaneous injection of CCl for 6 weeks. Prevention experiment and treatment experiment were administered with specific drugs at different times. At the end of treatment experiment, the pathological changes of liver were observed after hematoxylin-eosin staining. The expressions of ingredients in renin-angiotensin-aldosterone system (RAAS) such as AngII, Ang-(1-7), ACE, ACE2, AT1R, Mas, renin, CYP11B2 and angen in liver were detected by enzyme linked immunosorbent assay, immunohistochemistry method or reverse transcription-polymerase chain reaction, respectively.</p><p><b>RESULTS</b>The levels of AngII and Ang-(1-7) at the 6th week increased by 496.10% and 73.64%, respectively, compared with those at the 2nd week in the model group (P<0.01). With prevention or treatment with high-dosage BOL, there was an evident reduction of AngII level but an improvement of Ang-(1-7) level. Specifically, AngII level of high-dosage group decreased by 77.50% in prevention experiment (P=0.000) and by 76.93% in treatment experiment (P=0.002) compared with that in the model group. Ang-(1-7) level increased by 91.69% in prevention experiment (P=0.006) and by 70.77% in the treatment experiment (P=0.010) compared with that in the model group. The expression levels of mRNA of renin, ACE, CYP11B2, angen and AT1R decreased by 58.15%, 99.90%, 99.84%, 99.99% and 99.99% (all P<0.01), respectively.</p><p><b>CONCLUSIONS</b>BOL could help resist liver fibrosis in rats by enhancing the level of each ingredient in ACE2-Ang-(1-7)-Mas axis, while decreasing the level of each ingredient in ACE-AngII-AT1R axis. To some extent, BOL could enhance the regulation of RAAS in rats with CCl-induced hepatic fibrosis.</p>

Global Perspectives on Children's Digital Opportunities: An Emerging Research and Policy Agenda.

Diverse international perspectives show that children can benefit greatly from digital opportunities. Despite widespread optimism about the potential of digital technologies, especially for information and education, the research reveals an insufficient evidence base to guide policy and practice across all continents of the world, especially in middle- and low-income countries. Beyond revealing pressing and sizeable gaps in knowledge, this cross-national review also reveals the importance of understanding local values and practices regarding the use of technologies. This leads us to stress that future researchers must take into account local contexts and existing inequalities and must share best practices internationally so that children can navigate the balance between risks and opportunities. This article documents the particular irony that while the world's poorer countries look to research to find ways to increase access and accelerate the fair distribution of digital educational resources, the world's wealthier countries look to research for guidance in managing excessive screen time, heavily commercial content, and technologies that intrude on autonomy and privacy. We conclude by recommending that digital divides should be carefully bridged with contextual sensitivity to avoid exacerbating existing disparities; that the provision of technological resources is complemented by a focus on skills enhancement, for teachers as well as students; that a keen eye is needed to ensure the balance of children's protection and participation rights, with protection now including data abuses as well as safety considerations; and that we forge collaborations among all stakeholders in seeking to enhance children's digital opportunities worldwide.

Optic Disc Localization Using Directional Models.

Reliable localization of the optic disc (OD) is important for retinal image analysis and ophthalmic pathology screening. This paper presents a novel method to automatically localize ODs in retinal fundus images based on directional models. According to the characteristics of retina vessel networks, such as their origin at the OD and parabolic shape of the main vessels, a global directional model, named the relaxed biparabola directional model, is first built. In this model, the main vessels are modeled by using two parabolas with a shared vertex and different parameters. Then, a local directional model, named the disc directional model, is built to characterize the local vessel convergence in the OD as well as the shape and the brightness of the OD. Finally, the global and the local directional models are integrated to form a hybrid directional model, which can exploit the advantages of the global and local models for highly accurate OD localization. The proposed method is evaluated on nine publicly available databases, and achieves an accuracy of 100% for each database, which demonstrates the effectiveness of the proposed OD localization method.

PFR peptide, one of the antimicrobial peptides identified from the derivatives of lactoferrin, induces necrosis in leukemia cells.

LF11-322 (PFWRIRIRR-NH2) (PFR peptide), a nine amino acid-residue peptide fragment derived from human lactoferricin, possesses potent cytotoxicity against bacteria. We report here the discovery and characterization of its antitumor activity in leukemia cells. PFR peptide inhibited the proliferation of MEL and HL-60 leukemia cells by inducing cell death in the absence of the classical features of apoptosis, including chromatin condensation, Annexin V staining, Caspase activation and increase of abundance of pro-apoptotic proteins. Instead, necrotic cell death as evidenced by increasing intracellular PI staining and LDH release, inducing membrane disruption and up-regulating intracellular calcium level, was observed following PFR peptide treatment. In addition to necrotic cell death, PFR peptide also induced G0/G1 cell cycle arrest. Moreover, PFR peptide exhibited favorable antitumor activity and tolerability in vivo. These findings thus provide a new clue of antimicrobial peptides as a potential novel therapy for leukemia.

Value of serum procalcitonin levels in predicting spontaneous bacterial peritonitis.

BACKGROUND/AIMS: Spontaneous bacterial peritonitis (SBP) is a life-threatening disease that poses a great diagnostic challenge to clinicians. We aimed to systemically and quantitatively summarize the current evidence on the diagnostic value of the procalcitonin (PCT) test in identifying SBP. METHODOLOGY: We searched EMBASE, MEDLINE, the Cochrane database and reference lists of relevant articles with no language restrictions through May 2012. We selected original research that reported the diagnostic performance of PCT alone or compared with other biomarkers to diagnose SBP. We summarized test performance characteristics using forest plots, summary receiver operating characteristic curves and bivariate random effects models. RESULTS: We found only three qualifying studies examining 181 episodes of suspected infection with 50 (27.6%) confirmed SBP episodes from 3 countries. Bivariate pooled sensitivity, specificity, positive likelihood ratios and negative likelihood ratios were 86% (95%CI: 73%-94%), 80% (95%CI: 72%-87%), 7.73 (95%CI: 0.91-65.64) and 0.14 (95%CI: 0.01-1.89), respectively. The global measures of accuracy, area under the receiver operating curve (AUROC) and diagnostic odds ratio (DOR), showed PCT has excellent discriminative capability and individual study showed serum PCT testing has better accuracy than ascitic PCT, serum CRP or IL-6 testing. There was evidence of significant heterogeneity but no evidence of publication bias. CONCLUSIONS: The existing literature suggests moderate to high accuracy for PCT as a diagnostic aid for SBP. However, larger, appropriately designed prospective studies are needed to conclusively address the value of serum PCT testing in SBP diagnosis.