Vaccination induces broadly neutralizing antibody precursors to HIV gp41.

A key barrier to the development of vaccines that induce broadly neutralizing antibodies (bnAbs) against human immunodeficiency virus (HIV) and other viruses of high antigenic diversity is the design of priming immunogens that induce rare bnAb-precursor B cells. The high neutralization breadth of the HIV bnAb 10E8 makes elicitation of 10E8-class bnAbs desirable; however, the recessed epitope within gp41 makes envelope trimers poor priming immunogens and requires that 10E8-class bnAbs possess a long heavy chain complementarity determining region 3 (HCDR3) with a specific binding motif. We developed germline-targeting epitope scaffolds with affinity for 10E8-class precursors and engineered nanoparticles for multivalent display. Scaffolds exhibited epitope structural mimicry and bound bnAb-precursor human naive B cells in ex vivo screens, protein nanoparticles induced bnAb-precursor responses in stringent mouse models and rhesus macaques, and mRNA-encoded nanoparticles triggered similar responses in mice. Thus, germline-targeting epitope scaffold nanoparticles can elicit rare bnAb-precursor B cells with predefined binding specificities and HCDR3 features.

Cellular bases of olfactory circuit assembly revealed by systematic time-lapse imaging.

Neural circuit assembly features simultaneous targeting of numerous neuronal processes from constituent neuron types, yet the dynamics is poorly understood. Here, we use the Drosophila olfactory circuit to investigate dynamic cellular processes by which olfactory receptor neurons (ORNs) target axons precisely to specific glomeruli in the ipsi- and contralateral antennal lobes. Time-lapse imaging of individual axons from 30 ORN types revealed a rich diversity in extension speed, innervation timing, and ipsilateral branch locations and identified that ipsilateral targeting occurs via stabilization of transient interstitial branches. Fast imaging using adaptive optics-corrected lattice light-sheet microscopy showed that upon approaching target, many ORN types exhibiting "exploring branches" consisted of parallel microtubule-based terminal branches emanating from an F-actin-rich hub. Antennal nerve ablations uncovered essential roles for bilateral axons in contralateral target selection and for ORN axons to facilitate dendritic refinement of postsynaptic partner neurons. Altogether, these observations provide cellular bases for wiring specificity establishment.

Induction of HIV Neutralizing Antibody Lineages in Mice with Diverse Precursor Repertoires.

The design of immunogens that elicit broadly reactive neutralizing antibodies (bnAbs) has been a major obstacle to HIV-1 vaccine development. One approach to assess potential immunogens is to use mice expressing precursors of human bnAbs as vaccination models. The bnAbs of the VRC01-class derive from the IGHV1-2 immunoglobulin heavy chain and neutralize a wide spectrum of HIV-1 strains via targeting the CD4 binding site of the envelope glycoprotein gp120. We now describe a mouse vaccination model that allows a germline human IGHV1-2(∗)02 segment to undergo normal V(D)J recombination and, thereby, leads to the generation of peripheral B cells that express a highly diverse repertoire of VRC01-related receptors. When sequentially immunized with modified gp120 glycoproteins designed to engage VRC01 germline and intermediate antibodies, IGHV1-2(∗)02-rearranging mice, which also express a VRC01-antibody precursor light chain, can support the affinity maturation of VRC01 precursor antibodies into HIV-neutralizing antibody lineages.

Vaccination induces maturation in a mouse model of diverse unmutated VRC01-class precursors to HIV-neutralizing antibodies with >50% breadth.

Vaccine elicitation of broadly neutralizing antibodies (bnAbs) is a key HIV-research goal. The VRC01 class of bnAbs targets the CD4-binding site on the HIV-envelope trimer and requires extensive somatic hypermutation (SHM) to neutralize effectively. Despite substantial progress, vaccine-induced VRC01-class antibodies starting from unmutated precursors have exhibited limited neutralization breadth, particularly against viruses bearing glycan on loop D residue N276 (glycan276), present on most circulating strains. Here, using sequential immunization of immunoglobulin (Ig)-humanized mice expressing diverse unmutated VRC01-class antibody precursors, we elicited serum responses capable of neutralizing viruses bearing glycan276 and isolated multiple lineages of VRC01-class bnAbs, including two with >50% breadth on a 208-strain panel. Crystal structures of representative bnAbs revealed the same mode of recognition as known VRC01-class bnAbs. Structure-function studies further pinpointed key mutations and correlated their induction with specific immunizations. VRC01-class bnAbs can thus be matured by sequential immunization from unmutated ancestors to >50% breadth, and we delineate immunogens and regimens inducing key SHM.

Glycan Masking Focuses Immune Responses to the HIV-1 CD4-Binding Site and Enhances Elicitation of VRC01-Class Precursor Antibodies.

An important class of HIV-1 broadly neutralizing antibodies, termed the VRC01 class, targets the conserved CD4-binding site (CD4bs) of the envelope glycoprotein (Env). An engineered Env outer domain (OD) eOD-GT8 60-mer nanoparticle has been developed as a priming immunogen for eliciting VRC01-class precursors and is planned for clinical trials. However, a substantial portion of eOD-GT8-elicited antibodies target non-CD4bs epitopes, potentially limiting its efficacy. We introduced N-linked glycans into non-CD4bs surfaces of eOD-GT8 to mask irrelevant epitopes and evaluated these mutants in a mouse model that expressed diverse immunoglobulin heavy chains containing human IGHV1-2∗02, the germline VRC01 VH segment. Compared to the parental eOD-GT8, a mutant with five added glycans stimulated significantly higher proportions of CD4bs-specific serum responses and CD4bs-specific immunoglobulin G+ B cells including VRC01-class precursors. These results demonstrate that glycan masking can limit elicitation of off-target antibodies and focus immune responses to the CD4bs, a major target of HIV-1 vaccine design.

Humanized V(D)J-rearranging and TdT-expressing mouse vaccine models with physiological HIV-1 broadly neutralizing antibody precursors.

Antibody heavy chain (HC) and light chain (LC) variable region exons are assembled by V(D)J recombination. V(D)J junctional regions encode complementarity-determining-region 3 (CDR3), an antigen-contact region immensely diversified through nontemplated nucleotide additions ("N-regions") by terminal deoxynucleotidyl transferase (TdT). HIV-1 vaccine strategies seek to elicit human HIV-1 broadly neutralizing antibodies (bnAbs), such as the potent CD4-binding site VRC01-class bnAbs. Mice with primary B cells that express receptors (BCRs) representing bnAb precursors are used as vaccination models. VRC01-class bnAbs uniformly use human HC VH1-2 and commonly use human LCs Vκ3-20 or Vκ1-33 associated with an exceptionally short 5-amino-acid (5-aa) CDR3. Prior VRC01-class models had nonphysiological precursor levels and/or limited precursor diversity. Here, we describe VRC01-class rearranging mice that generate more physiological primary VRC01-class BCR repertoires via rearrangement of VH1-2, as well as Vκ1-33 and/or Vκ3-20 in association with diverse CDR3s. Human-like TdT expression in mouse precursor B cells increased LC CDR3 length and diversity and also promoted the generation of shorter LC CDR3s via N-region suppression of dominant microhomology-mediated Vκ-to-Jκ joins. Priming immunization with eOD-GT8 60mer, which strongly engages VRC01 precursors, induced robust VRC01-class germinal center B cell responses. Vκ3-20-based responses were enhanced by N-region addition, which generates Vκ3-20-to-Jκ junctional sequence combinations that encode VRC01-class 5-aa CDR3s with a critical E residue. VRC01-class-rearranging models should facilitate further evaluation of VRC01-class prime and boost immunogens. These new VRC01-class mouse models establish a prototype for the generation of vaccine-testing mouse models for other HIV-1 bnAb lineages that employ different HC or LC Vs.

A Prelimbic Cortex-Thalamus Circuit Bidirectionally Regulates Innate and Stress-induced Anxiety-like Behavior.

Anxiety-related disorders respond to cognitive behavioral therapies, which involved the medial prefrontal cortex (mPFC). Previous studies have suggested that subregions of the mPFC have different and even opposite roles in regulating innate anxiety. However, the specific causal targets of their descending projections in modulating innate anxiety and stress-induced anxiety have yet to be fully elucidated. Here, we found that among the various downstream pathways of the prelimbic cortex (PL), a subregion of the mPFC, PL-mediodorsal thalamic nucleus (MD) projection and PL-ventral tegmental area (VTA) projection exhibited antagonistic effects on anxiety-like behavior, while the PL-MD projection but not PL-VTA projection was necessary for the animal to guide anxiety-related behavior. In addition, MD-projecting PL neurons bidirectionally regulated remote but not recent fear memory retrieval. Notably, restraint stress induced high-anxiety state accompanied by strengthening the excitatory inputs onto MD-projecting PL neurons, and inhibiting PL-MD pathway rescued the stress-induced anxiety. Our findings reveal that the activity of PL-MD pathway may be an essential factor to maintain certain level of anxiety, and stress increased the excitability of this pathway, leading to inappropriate emotional expression, and suggest that targeting specific PL circuits may aid the development of therapies for the treatment of stress-related disorders.Significance statement This study provides insight into PL downstream pathways for regulating innate and stress-induced anxiety-like behavior. We reported that PL-mediodorsal thalamic nucleus (MD) projection and PL-ventral tegmental area (VTA) projection exhibited antagonistic effects on anxiety-like behavior, while the PL-MD projection but not PL-VTA projection was necessary for the animal to guide anxiety-related behavior. In addition, this study provides definite evidence that MD-projecting PL neurons bidirectionally regulated remote fear memory retrieval and concordant with a role for the PL-MD in anxiety. Moreover, this study is the first demonstration that restraint stress induced high-anxiety state accompanied by strengthening the excitatory inputs onto MD-projecting PL neurons, and inhibiting PL-MD pathway rescued the stress-induced anxiety.

TrieDedup: a fast trie-based deduplication algorithm to handle ambiguous bases in high-throughput sequencing.

BACKGROUND: High-throughput sequencing is a powerful tool that is extensively applied in biological studies. However, sequencers may produce low-quality bases, leading to ambiguous bases, 'N's. PCR duplicates introduced in library preparation are conventionally removed in genomics studies, and several deduplication tools have been developed for this purpose. Two identical reads may appear different due to ambiguous bases and the existing tools cannot address 'N's correctly or efficiently. RESULTS: Here we proposed and implemented TrieDedup, which uses the trie (prefix tree) data structure to compare and store sequences. TrieDedup can handle ambiguous base 'N's, and efficiently deduplicate at the level of raw sequences. We also reduced its memory usage by approximately 20% by implementing restrictedDict in Python. We benchmarked the performance of the algorithm and showed that TrieDedup can deduplicate reads up to 270-fold faster than pairwise comparison at a cost of 32-fold higher memory usage. CONCLUSIONS: The TrieDedup algorithm may facilitate PCR deduplication, barcode or UMI assignment, and repertoire diversity analysis of large-scale high-throughput sequencing datasets with its ultra-fast algorithm that can account for ambiguous bases due to sequencing errors.

Mature astrocytes as source for astrocyte repopulation after deletion in the medial prefrontal cortex: Implications for depression.

The adult brain retains a high repopulation capacity of astrocytes after deletion, and both mature astrocytes in the neocortex and neural stem cells in neurogenic regions possess the potential to generate astrocytes. However, the origin and the repopulation dynamics of the repopulating astrocytes after deletion remain largely unclear. The number of astrocytes is reduced in the medial prefrontal cortex (mPFC) of patients with depression, and selective elimination of mPFC astrocytes is sufficient to induce depression-like behaviors in rodents. However, whether astrocyte repopulation capacity is impaired in depression is unknown. In this study, we used different transgenic mouse lines to genetically label different cell types and demonstrated that in the mPFC of normal adult mice of both sexes, mature astrocytes were a major source of the repopulating astrocytes after acute deletion induced by an astrocyte-specific toxin, L-alpha-aminoadipic acid (L-AAA), and astrocyte regeneration was accomplished within two weeks accompanied by reversal of depression-like behaviors. Furthermore, re-ablation of mPFC astrocytes post repopulation led to reappearance of depression-like behaviors. In adult male mice subjected to 14-day chronic restraint stress, a well-validated mouse model of depression, the number of mPFC astrocytes was reduced; however, the ability of mPFC astrocytes to repopulate after L-AAA-induced deletion was largely unaltered. Our study highlights a potentially beneficial role for repopulating astrocytes in depression and provides novel therapeutic insights into enhancing local mature astrocyte generation in depression.

Dopamine D2 receptors in pyramidal neurons in the medial prefrontal cortex regulate social behavior.

Drugs acting on dopamine D2 receptors are widely used for the treatment of several neuropsychiatric disorders, including schizophrenia and depression. Social deficits are a core symptom of these disorders. Pharmacological manipulation of dopamine D2 receptors (Drd2), a Gi-coupled subtype of dopamine receptors, in the medial prefrontal cortex (mPFC) has shown that Drd2 is implicated in social behaviors. However, the type of neurons expressing Drd2 in the mPFC and the underlying circuit mechanism regulating social behaviors remain largely unknown. Here, we show that Drd2 were mainly expressed in pyramidal neurons in the mPFC and that the activation of the Gi-pathway in Drd2+ pyramidal neurons impaired social behavior in male mice. In contrast, the knockdown of D2R in pyramidal neurons in the mPFC enhanced social approach behaviors in male mice and selectively facilitated the activation of mPFC neurons projecting to the nucleus accumbens (NAc) during social interaction. Remarkably, optogenetic activation of mPFC-to-NAc-projecting neurons mimicked the effects of conditional D2R knockdown on social behaviors. Altogether, these results demonstrate a cell type-specific role for Drd2 in the mPFC in regulating social behavior, which may be mediated by the mPFC-to-NAc pathway.

Group A Streptococcal meningitis in children: a short case series and systematic review.

BACKGROUND: Group A streptococcal(GAS) meningitis is a severe disease with a high case fatality rate. In the era of increasing GAS meningitis, our understanding about this disease is limited. PURPOSE: To gain a better understanding about GAS meningitis. METHODS: Five new cases with GAS meningitis were reported. GAS meningitis related literatures were searched for systematic review in PUBMED and EMBASE. Case reports and case series on paediatric cases were included. Information on demographics, risk factors, symptoms, treatments, outcomes, and emm types of GAS was summarized. RESULTS: Totally 263 cases were included. Among 100 individuals, 9.9% (8/81) had prior varicella, 11.1% (9/81) had anatomical factors, and 53.2% (42/79) had extracranial infections. Soft tissue infections were common among infants (10/29, 34.5%), while ear/sinus infections were more prevalent in children ≥ 3 years (21/42, 50.0%). The overall case fatality rate (CFR) was 16.2% (12/74). High risk of death was found in patients with shock or systemic complications, young children(< 3 years) and cases related to hematogenic spread. The predominate cause of death was shock(6/8). Among the 163 patients included in case series studies, ear/sinus infections ranged from 21.4 to 62.5%, while STSS/shock ranged from 12.5 to 35.7%, and the CFR ranged from 5.9 to 42.9%. CONCLUSIONS: A history of varicella, soft tissue infections, parameningeal infections and CSF leaks are important clinical clues to GAS in children with meningitis. Young children and hematogenic spread related cases need to be closely monitored for shock due to the high risk of death.

Synthesis, biological activity evaluation and mechanism of action of novel bis-isatin derivatives as potential anti-liver cancer agents.

A series of bis-isatin conjugates with lysine linker were synthesized with the aim of probing their antiproliferative potential. All the newly synthesized derivatives (0-100 µM) were first screened against liver cancer cell lines(Huh1, H22, Huh7, Hepa1-6, HepG2, Huh6 and 97H) using CCK-8 assay. Results indicated that the derivative 4d exhibited the most potent activity against Huh1 (IC50 = 17.13 µM) and Huh7(IC50 = 8.265 µM). In vivo anti-tumor study showed that compound 4d effectively inhibited tumor growth in Huh1-induced xenograft mouse model; the anti-tumor effect of compound 4d (15 mg/kg) was comparable with sorafenib (20 mg/kg). H&E staining analysis and routine blood test and blood serum biochemistry examination was performed to confirm the safety of compound 4d in xenograft models. The mechanism of action of 4d on tumor growth inhibition was further investigated by RNA-Seq analysis, which indicates a positive regulation of autophagy signaling pathway, which was further confirmed with key biomarker expression of autophagy after 4d treatment. Our results suggest that the bis-isatin conjugate compound 4d is a promising tumor inhibitory agent for some liver cancer.

Integrative ATAC-seq and RNA-seq analysis associated with diabetic nephropathy and identification of novel targets for treatment by dapagliflozin.

Dapagliflozin (DAPA) are clinically effective in improving diabetic nephropathy (DN). However, whether and how chromatin accessibility changed by DN responds to DAPA treatment is unclear. Therefore, we performed ATAC-seq, RNA-seq, and weighted gene correlation network analysis to identify the chromatin accessibility, the messenger RNA (mRNA) expression, and the correlation between clinical phenotypes and mRNA expression using kidney from three mouse groups: db/m mice (Controls), db/db mice (case group), and those treated with DAPA (treatment group). RNA-Seq and ATAC-seq conjoint analysis revealed many overlapping pathways and networks suggesting that the transcriptional changes of DN and DAPA intervention largely occured dependently on chromatin remodeling. Specifically, the results showed that some key signal transduction pathways, such as immune dysfunction, glucolipid metabolism, oxidative stress and xenobiotic and endobiotic metabolism, were repeatedly enriched in the analysis of the RNA-seq data alone, as well as combined analysis with ATAC-seq data. Furthermore, we identified some candidate genes (UDP glucuronosyltransferase 1 family, Dock2, Tbc1d10c, etc.) and transcriptional regulators (KLF6 and GFI1) that might be associated with DN and DAPA restoration. These reversed genes and regulators confirmed that pathways related to immune response and metabolism pathways were critically involved in DN progression.

An in vivo method for diversifying the functions of therapeutic antibodies.

V(D)J recombination generates mature B cells that express huge repertoires of primary antibodies as diverse immunoglobulin (Ig) heavy chain (IgH) and light chain (IgL) of their B cell antigen receptors (BCRs). Cognate antigen binding to BCR variable region domains activates B cells into the germinal center (GC) reaction in which somatic hypermutation (SHM) modifies primary variable region-encoding sequences, with subsequent selection for mutations that improve antigen-binding affinity, ultimately leading to antibody affinity maturation. Based on these principles, we developed a humanized mouse model approach to diversify an anti-PD1 therapeutic antibody and allow isolation of variants with novel properties. In this approach, component Ig gene segments of the anti-PD1 antibody underwent de novo V(D)J recombination to diversify the anti-PD1 antibody in the primary antibody repertoire in the mouse models. Immunization of these mouse models further modified the anti-PD1 antibodies through SHM. Known anti-PD1 antibodies block interaction of PD1 with its ligands to alleviate PD1-mediated T cell suppression, thereby boosting antitumor T cell responses. By diversifying one such anti-PD1 antibody, we derived many anti-PD1 antibodies, including anti-PD1 antibodies with the opposite activity of enhancing PD1/ligand interaction. Such antibodies theoretically might suppress deleterious T cell activities in autoimmune diseases. The approach we describe should be generally applicable for diversifying other therapeutic antibodies.

Effect of Different Local Antibiotic Regimens on Prevention of Postoperative Infection in Clean Surgical Wounds: A Systematic Review and Network Meta-analysis.

OBJECTIVE: To compare the efficacy of several local antibiotic regimens in preventing surgical site infection (SSI) in clean surgical wounds. DATA SOURCES: The authors searched CNKI (China National Knowledge Infrastructure), the VIP (VIP information resource integration service platform), Wanfang Data knowledge service platform (WANFANG), SinoMed, Cochrane Library, EMBASE, and PubMed. STUDY SELECTION: A total of 20 randomized controlled trials published between January 1, 2000 and April 1, 2021 were included in this meta-analysis. DATA EXTRACTION: Authors extracted the name of the first author, publication date, country, type of surgery, follow-up time, mean age of participants, sample size of each group, interventions, outcome indicators, and study type from each article. DATA SYNTHESIS: The overall effectiveness of eight local managements in reducing the incidence of the SSI effect were compared through the SUCRA (surface under the cumulative ranking curve) probabilities. The results of a network meta-analysis demonstrated that gentamicin ointment (odds ratio [OR], 0.16; 95% CI, 0.04-0.60), mupirocin ointment (OR, 0.44; 95% CI, 0.21-0.94), and gentamicin soaking of the graft (OR, 0.63; 95% CI, 0.44-0.91) significantly reduced the incidence of SSI compared with control. Further, vancomycin soaking of the graft (86.7%) ranked first, followed by gentamicin ointment (81.1%), gentamicin irrigation (79.9%), mupirocin ointment (56.8%), triple antibiotic ointment (47.8%), gentamicin soaking of the graft (42.3%), and vancomycin powder (22.1%); ampicillin powder (17.8%) was the least effective drug. CONCLUSIONS: The findings indicate that local antibiotics combined with conventional antibiotics in the wound before wound closure are effective in reducing the incidence of SSI in clean surgical wounds. Vancomycin inoculation of the graft exhibited the best effect.

[Mechanism of n-butanol extract of Pulsatilla Decoction in treating ulcerative colitis by activating BMP signaling pathway].

The study aimed to investigate the therapeutic effects of the n-butanol extract of Pulsatilla Decoction(BEPD) on ulcerative colitis(UC) via the bone morphogenetic protein(BMP) signaling pathway. C57BL/6 mice were divided into six groups: control, model, mesalazine, and BEPD low-, medium-, and high-dose groups. Except for the control group, the rest groups were treated with 3% dextran sulfate sodium(DSS) freely for seven consecutive days to establish the UC mouse model, followed by treatment with different concentrations of BEPD and mesalazine by gavage. The murine body weight and disease activity index(DAI) were recorded. After the mice were sacrificed, their colon tissues were collected for histological analysis. Alcian blue/periodic acid-Schiff(AB/PAS) staining was used to detect the number and mucus secretion status of goblet cells; immunohistochemistry was performed to measure the expression of ki67, cleaved caspase-3, mucin 2(Muc2), and matrix metalloproteinase-9(MMP9) in colon tissues; and immunofluorescence was used to analyze the expression of tight junction proteins in colon tissues, and enzyme linked immunosorbent assay(ELISA) was employed to quantify the levels of tumor necrosis factor-α(TNF-α), interleukin(IL)-1ß, and IL-6. Western blot was conducted to evaluate the expression of BMP pathway-related proteins in mouse colon tissues. Quantitative real-time PCR(qRT-PCR) was performed to measure the expression of genes related to goblet cell differentiation in mouse colon tissues. In addition, this study also examined the protective effect and underlying mechanism of BEPD-containing serum on lipopolysaccharide(LPS)-induced barrier damages in LS174T goblet cells in vitro. The results showed that BEPD significantly alleviated UC symptoms in mice, restored goblet cell diffe-rentiation function, promoted Muc2 secretion and tight junction protein expression, and suppressed inflammatory factor secretion while activating the BMP signaling pathway. Therefore, BEPD may exert its therapeutic effects on UC by activating the BMP signaling pathway, providing a new strategy for drug intervention in UC.

EphB6 deficiency in intestinal neurons promotes tumor growth in colorectal cancer by neurotransmitter GABA signaling.

EphB6 belongs to the receptor tyrosine kinase, whose low expression is associated with shorter survival of colorectal cancer (CRC) patients. But the role and mechanism of EphB6 in the progression of CRC need further study. In addition, EphB6 was mainly expressed in intestinal neurons. But how EphB6 is involved in functions of intestinal neurons has not been known. In our study, we constructed a mouse xenograft model of CRC by injecting CMT93 cells into the rectum of EphB6-deficient mice. We found that the deletion of EphB6 in mice promoted tumor growth of CMT93 cells in a xenograft model of CRC, which was independent of changes in the gut microbiota. Interestingly, inhibition of intestinal neurons by injecting botulinum toxin A into rectum of EphB6-deficient mice could eliminate the promotive effect of EphB6 deficiency on tumor growth in the xenograft model of CRC. Mechanically, the deletion of EphB6 in mice promoted the tumor growth in CRC by increasing GABA in the tumor microenvironment. Furthermore, EphB6 deficiency in mice increased the expression of synaptosomal-associated protein 25 in the intestinal myenteric plexus, which mediated the release of GABA. Our study concluded that EphB6 knockout in mice promotes tumor growth of CMT93 cells in a xenograft model of CRC by modulating GABA release. Our study found a new regulating mechanism of EphB6 on the tumor progression in CRC that is dependent on intestinal neurons.

Two-color unidirectional reflections by modulating the spatial susceptibility in a homogeneous atomic medium.

Non-reciprocal reflections of optical signals are unusual yet fascinating to achieve the imminent applications of non-reciprocal photonic devices and circuits. The complete non-reciprocal reflection (unidirectional reflection) was recently found to be achievable in a homogeneous medium, if the real and imaginary parts of the probe susceptibility satisfy the spatial Kramers-Kronig (KK) relation. We propose a coherent four-level tripod model for realizing dynamically tunable two-color non-reciprocal reflections by applying two control fields with linearly modulated intensities. We found that, the unidirectional reflection can be obtained if the non-reciprocal frequency regions are located in the electromagnetically induced transparency (EIT) windows. This mechanism is to break the spatial symmetry by the spatial modulation of susceptibility to induce unidirectional reflections, the real and imaginary parts of the probe susceptibility are no longer required to satisfy the spatial KK relation.

Characterization and pathogenicity of the porcine epidemic diarrhea virus isolated in China.

Piglet diarrhea caused by the porcine epidemic diarrhea virus (PEDV) is a common problem on pig farms in China associated with high morbidity and mortality rates. In this study, three PEDV isolates were successfully detected after the fourth blind passage in Vero cells. The samples were obtained from infected piglet farms in Jilin (Changchun), and Shandong (Qingdao) Provinces of China and were designated as CH/CC-1/2018, CH/CC-2/2018, and CH/QD/2018. According to the analysis of the complete S protein gene sequence, the CH/CC-1/2018 and CH/CC-2/2018 were allocated to the G2b branch, while CH/QD/2018 was located in the G1a interval and was closer to the vaccine strain CV777. Successful detection and identification of the isolated strains were carried out using electron microscopy and indirect immunofluorescence. Meanwhile, animal challenge experiments and viral RNA copies determination were used to compare the pathogenicity. The results showed that CH/CC-1/2018 in Changchun was more pathogenic than CH/QD/2018 in Qingdao. In conclusion, the discovery of these new strains is conducive to the development of vaccines to prevent the pandemic of PEDV, especially that the CH/CC-1/2018, and CH/CC-2/2018 were not related to the classical vaccine strain CV777.