• Intestinal mucus
• Mucosal immunology
• Viral gastroenteritis
• Virus-blocking
• Virus-mucus interaction

• Higher Education Commision, Pakistan
• Instytut Immunologii i Terapii Doświadczalnej, im. Ludwika Hirszfelda Polskiej Akademii Nauk

• innate immunity
• porcine epidemic diarrhea virus (PEDV)
• protein function
• viral proteins

• Animals
• Swine
• Female
• Porcine epidemic diarrhea virus
• Coronavirus Infections/veterinary
• Viral Proteins
• Diarrhea/veterinary
• Vaccines

• P20211154-030303 Lingnan Modern Agricultural Science and Technology Guangdong Provincial Laboratory Zhaoqing Branch 's ' 14th Five-Year ' Independent Project
• 2023B10564003 Double first-class discipline promotion project
• 2019B020218004 the Guangdong Key Research and Development Program

• coronavirus
• feline coronavirus
• furin cleavage
• positive selection
• tropism shift

• R01 AI134384 NIAID NIH HHS
• T32 EB023860 NIBIB NIH HHS
• U18 FD006993 FDA HHS
• National Institute of Biomedical and Bioengineering
• NIH/NIAID
• FDA Vet-LIRN

• R01 AI134384 NIAID NIH HHS
• T32 EB023860 NIBIB NIH HHS
• U18 FD006993 FDA HHS

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the causative agent of the newly emerging lung disease pandemic COVID-19. This viral infection causes a series of respiratory disorders, and although this virus mainly infects respiratory cells, the small intestine can also be an important site of entry or interaction, as enterocytes highly express in angiotensin-2 converting enzyme (ACE) receptors. There are countless reports pointing to the importance of interferons (IFNs) with regard to the mediation of the immune system in viral infection by SARS-CoV-2. Thus, this review will focus on the main cells that make up the large intestine, their specific immunology, as well as the function of IFNs in the intestinal mucosa after the invasion of coronavirus-2.

• COVID-19
• Gastrointestinal Diseases/diagnosis
• Gastrointestinal Diseases/epidemiology
• Gastrointestinal Diseases/etiology
• Humans
• Prevalence
• SARS-CoV-2
• Vomiting/epidemiology
• Vomiting/etiology

Porcine deltacoronavirus (PDCoV) is a novel coronavirus that causes diarrhea in nursing piglets. Studies showed that PDCoV uses porcine aminopeptidase N (pAPN) as an entry receptor, but the infection of pAPN-knockout cells or pigs with PDCoV revealed that pAPN might be not a critical functional receptor, implying there exists an unidentified receptor involved in PDCoV infection. Herein, we report that sialic acid (SA) can act as an attachment receptor for PDCoV invasion and facilitate its infection. We first demonstrated that the carbohydrates destroyed on the cell membrane using NaIO₄ can alleviate the susceptibility of cells to PDCoV. Further study showed that the removal of SA, a typical cell-surface carbohydrate, could influence the PDCoV infectivity to the cells significantly, suggesting that SA was involved in the infection. The results of plaque assay and Western blotting revealed that SA promoted PDCoV infection by increasing the number of viruses binding to SA on the cell surface during the adsorption phase, which was also confirmed by atomic force microscopy at the microscopic level. In in vivo experiments, we found that the distribution levels of PDCoV and SA were closely relevant in the swine intestine, which contains huge amount of trypsin. We further confirmed that SA-binding capacity to PDCoV is related to the pre-treatment of PDCoV with trypsin. In conclusion, SA is a novel attachment receptor for PDCoV infection to enhance its attachment to cells, which is dependent on the pre-treatment of trypsin on PDCoV. This study paves the way for dissecting the mechanisms of PDCoV–host interactions and provides new strategies to control PDCoV infection.

• carbohydrates
• porcine deltacoronavirus
• receptor
• sialic acid
• trypsin

• Animals
• Carbohydrates
• Cell Line
• Cell Membrane/metabolism
• Cell Membrane/virology
• Coronavirus Infections/veterinary
• Coronavirus Infections/virology
• Deltacoronavirus/drug effects
• Deltacoronavirus/physiology
• Host-Pathogen Interactions
• Intestines/metabolism
• Intestines/virology
• N-Acetylneuraminic Acid/metabolism
• Periodic Acid/pharmacology
• Receptors, Virus/metabolism
• Swine
• Swine Diseases/virology
• Trypsin/metabolism
• Trypsin/pharmacology
• Virus Attachment

Human coronaviruses present a substantial global disease burden, causing damage to populations’ health, economy, and social well-being. Glycans are one of the main structural components of all microbes and organismic structures, including viruses—playing multiple essential roles in virus infection and immunity. Studying and understanding virus glycans at the nanoscale provide new insights into the diagnosis and treatment of viruses. Glycan nanostructures are considered potential targets for molecular diagnosis, antiviral therapeutics, and the development of vaccines. This review article describes glycan nanostructures (eg, glycoproteins and glycolipids) that exist in cells, subcellular structures, and microbes. We detail the structure, characterization, synthesis, and functions of virus glycans. Furthermore, we describe the glycan nanostructures of different human coronaviruses, such as human coronavirus 229E (HCoV-229E), human coronavirus OC43 (HCoV-OC43), severe acute respiratory syndrome-associated coronavirus (SARS-CoV), human coronavirus NL63 (HCoV-NL63), human coronavirus HKU1 (HCoV-HKU1), the Middle East respiratory syndrome-associated coronavirus (MERS-CoV), and how glycan nanotechnology can be useful to prevent and combat human coronaviruses infections, along with possibilities that are not yet explored.

• SARS-CoV-2
• coronaviruses
• diagnostics
• glycan
• glycolipids
• glycoproteins
• nanotechnology
• vaccine

• COVID-19
• Coronavirus
• Gastrointestinal diseases
• Liver dysfunction
• Mechanisms
• SARS-CoV-2

• Coronavirus Infections/complications
• Digestive System Diseases/virology
• Host-Pathogen Interactions
• Humans
• SARS-CoV-2/physiology

The naturally isolated avian coronavirus infectious bronchitis virus (IBV) generally cannot replicate in chicken kidney (CK) cells. To explore the molecular mechanism of IBV adapting to CK cells, a series of recombinant viruses were constructed by chimerizing the S genes of CK cell-adapted strain H120 and non-adapted strain IBYZ. The results showed that the S2 subunit determines the difference in cell tropism of the two strains. After comparing the amino acid sequences of S protein of CK cell-adapted strain YZ120, with its parental strain IBYZ, three amino acid substitutions, A138V, L581F, and V617I, were identified. Using YZ120 as the backbone, one or more of the above-mentioned substitutions were eliminated to verify the correlation between these sites and CK cell tropism. The results showed that the CK cell tropism of the YZ120 strain depends on the V617I substitution, the change of L581F promoted the adaptation in CK cells, and the change at 138 position was not directly related to the CK cell tropism. Further validation experiments also showed that V617I had a decisive role in the adaptation of IBV to CK cells, but other areas of the virus genome also affected the replication efficiency of the virus in CK cells.

• CK cells
• amino acid mutation
• infectious bronchitis virus
• spike
• tropism

• coronavirus infections
• female
• infant
• lactoferrin
• pregnancy

Coronavirus disease 2019 (COVID-19) is spreading around the world, presenting mainly as respiratory symptoms. Some patients have obvious digestive system symptoms, or even present with only digestive system symptoms. Therefore, it is of great significance to clarify the digestive system manifestations in COVID-19 patients.

To explore the digestive system manifestations of 350 patients with COVID-19 hospitalized at our hospital, to provide reference for the diagnosis and treatment of COVID-19.

The data of 350 COVID-19 inpatients at our hospital, such as general conditions, initial symptoms, disease severity, digestive system symptoms, and liver function, were retrospectively analyzed. The digestive system symptoms and liver function indexes were compared between non-critically ill patients and critically ill patients. Statistical methods involved independent sample median test, continuity correction chi-square test, and one-way analysis of variance.

All the 350 patients were definitely diagnosed with COVID-19, including 176 (50.3%) males and 174 (49.7%) females. They ranged in age from 17 to 94 years, with a median age of 59 years. There were 254 (72.6%) non-critically ill patients and 96 (27.4%) critically ill patients. The initial symptoms were mainly fever, dry cough, fatigue, and chest tightness; 262 (74.9%) cases showed fever, 189 (54.0%) showed dry cough, 237 (67.7%) showed fatigue, and 195 (55.7%) showed chest tightness. Seventy-nine (22.6%) cases showed digestive system symptoms, mainly diarrhea, vomiting, and abdominal pain; 42 (12.0%) cases showed diarrhea, 48 (13.7%) showed vomiting, and 3 (0.9%) showed abdominal pain. Five (1.4%) cases presented with digestive system symptoms as the initial symptoms. One hundred and fifty (42.9%) cases had abnormal liver function indexes (increase in at least one of ALT, AST, TBIL, and DBIL), of which 73 (20.9%) had elevated ALT, 98 (28.0%) had elevated AST, 60 (17.1%) had elevated DBIL, and 27 (7.7%) had elevated TBIL. Serum albumin (ALB) was reduced in 275 (78.6%) patients. The percentage of non-critically ill patients with digestive system symptoms (52/254, 20.5%) was not statistically significant from that of critically ill patients (52/254 [20.5%] vs 27/96 [28.1%], χ² = 2.334, P > 0.05). The abnormal rate of liver function indexes (87/254, 34.3%) was significantly lower in non-critically ill patients than in critically ill patients (87/254 [34.3%] vs 63/96 [65.6%], χ² = 28, P < 0.05). The percentage of patients with ALB decline was significantly lower in non-critically ill patients than in critically ill patients (182/254 [71.7%] vs 93/96 [96.9%], χ² = 26.322, P < 0.05). In both non-critically ill and critically ill patients, the increase in liver function indexes was mostly not more than 2 × upper limit of normal, and ALB was mostly in the range of 30-40 g/L. Compared with the non-diarrhea group (236/308, 76.6%), the percentage of patients with ALB reduction in the diarrhea group (39/42, 92.9%) was statistically lower (χ² = 5.785, P < 0.05). There was no statistically significant difference in duration of onset between groups with different albumin concentrations (P > 0.05).

Hospitalized COVID-19 patients may show some digestive system symptoms, with diarrhea and vomiting being most common. A few patients present with digestive system symptoms as the initial manifestation, which is more likely to cause misdiagnosis. Some patients with COVID-19 show liver injury, although most of cases are mild, and no liver failure occurs. Compared with non-critically ill patients, the incidence of digestive system symptoms is generally similar to that of non-critically ill patients, but the incidence and degree of abnormal liver function indexes are higher in critically ill patients. Most patients with COVID-19 may have decreased serum albumin, and patients with diarrhea are more likely to have serum albumin decline. The above conclusions may help increase the awareness of COVID-19 among clinicians and improve their treatment skills.

• 2019-nCoV
• COVID-19
• Digestive system manifestation
• Liver function
• ALB

• COVID-19
• Diarrhea
• Pneumonia
• SARS-CoV-2

Since December 2019, a newly identified coronavirus (severe acute respiratory syndrome coronavirus (SARS-CoV-2)) has caused outbreaks of pneumonia in Wuhan, China. SARS-CoV-2 enters host cells via cell receptor ACE II (ACE2) and the transmembrane serine protease 2 (TMPRSS2). In order to identify possible prime target cells of SARS-CoV-2 by comprehensive dissection of ACE2 and TMPRSS2 coexpression pattern in different cell types, five datasets with single-cell transcriptomes of lung, oesophagus, gastric mucosa, ileum and colon were analysed.

Five datasets were searched, separately integrated and analysed. Violin plot was used to show the distribution of differentially expressed genes for different clusters. The ACE2-expressing and TMPRRSS2-expressing cells were highlighted and dissected to characterise the composition and proportion.

Cell types in each dataset were identified by known markers. ACE2 and TMPRSS2 were not only coexpressed in lung AT2 cells and oesophageal upper epithelial and gland cells but also highly expressed in absorptive enterocytes from the ileum and colon. Additionally, among all the coexpressing cells in the normal digestive system and lung, the expression of ACE2 was relatively highly expressed in the ileum and colon.

This study provides the evidence of the potential route of SARS-CoV-2 in the digestive system along with the respiratory tract based on single-cell transcriptomic analysis. This finding may have a significant impact on health policy setting regarding the prevention of SARS-CoV-2 infection. Our study also demonstrates a novel method to identify the prime cell types of a virus by the coexpression pattern analysis of single-cell sequencing data.

• infectious disease
• receptor binding
• medical decision analysis

Porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) have been reported to use aminopeptidase N (APN) as a cellular receptor. Recently, the role of APN as a receptor for PEDV has been questioned. In our study, the role of APN in PEDV and TGEV infections was studied in primary porcine enterocytes. After seven days of cultivation, 89% of enterocytes presented microvilli and showed a two- to five-fold higher susceptibility to PEDV and TGEV. A significant increase of PEDV and TGEV infection was correlated with a higher expression of APN, which was indicative that APN plays an important role in porcine coronavirus infections. However, PEDV and TGEV infected both APN positive and negative enterocytes. PEDV and TGEV Miller showed a higher infectivity in APN positive cells than in APN negative cells. In contrast, TGEV Purdue replicated better in APN negative cells. These results show that an additional receptor exists, different from APN for porcine coronaviruses. Subsequently, treatment of enterocytes with neuraminidase (NA) had no effect on infection efficiency of TGEV, implying that terminal cellular sialic acids (SAs) are no receptor determinants for TGEV. Treatment of TGEV with NA significantly enhanced the infection which shows that TGEV is masked by SAs.

• Porcine epidemic diarrhea virus (PEDV)
• aminopeptidase N
• enterocytes
• porcine coronavirus
• sialic acids
• transmissible gastroenteritis virus (TGEV)

MERS-CoV uses the S1^B domain of its spike protein to attach to its host receptor, dipeptidyl peptidase 4 (DPP4). The tissue localization of DPP4 has been mapped in different susceptible species. On the other hand, the S1^A domain, the N-terminal domain of this spike protein, preferentially binds to several glycotopes of α2,3-sialic acids, the attachment factor of MERS-CoV. Here we show, using a novel method, that the S1^A domain specifically binds to the nasal epithelium of dromedary camels, alveolar epithelium of humans, and intestinal epithelium of common pipistrelle bats. In contrast, it does not bind to the nasal epithelium of pigs or rabbits, nor does it bind to the intestinal epithelium of serotine bats and frugivorous bat species. This finding supports the importance of the S1^A domain in MERS-CoV infection and tropism, suggests its role in transmission, and highlights its potential use as a component of novel vaccine candidates.

Middle East respiratory syndrome coronavirus (MERS-CoV) uses the S1^B domain of its spike protein to bind to dipeptidyl peptidase 4 (DPP4), its functional receptor, and its S1^A domain to bind to sialic acids. The tissue localization of DPP4 in humans, bats, camelids, pigs, and rabbits generally correlates with MERS-CoV tropism, highlighting the role of DPP4 in virus pathogenesis and transmission. However, MERS-CoV S1^A does not indiscriminately bind to all α2,3-sialic acids, and the species-specific binding and tissue distribution of these sialic acids in different MERS-CoV-susceptible species have not been investigated. We established a novel method to detect these sialic acids on tissue sections of various organs of different susceptible species by using nanoparticles displaying multivalent MERS-CoV S1^A. We found that the nanoparticles specifically bound to the nasal epithelial cells of dromedary camels, type II pneumocytes in human lungs, and the intestinal epithelial cells of common pipistrelle bats. Desialylation by neuraminidase abolished nanoparticle binding and significantly reduced MERS-CoV infection in primary susceptible cells. In contrast, S1^A nanoparticles did not bind to the intestinal epithelium of serotine bats and frugivorous bat species, nor did they bind to the nasal epithelium of pigs and rabbits. Both pigs and rabbits have been shown to shed less infectious virus than dromedary camels and do not transmit the virus via either contact or airborne routes. Our results depict species-specific colocalization of MERS-CoV entry and attachment receptors, which may be relevant in the transmission and pathogenesis of MERS-CoV.

IMPORTANCE MERS-CoV uses the S1^B domain of its spike protein to attach to its host receptor, dipeptidyl peptidase 4 (DPP4). The tissue localization of DPP4 has been mapped in different susceptible species. On the other hand, the S1^A domain, the N-terminal domain of this spike protein, preferentially binds to several glycotopes of α2,3-sialic acids, the attachment factor of MERS-CoV. Here we show, using a novel method, that the S1^A domain specifically binds to the nasal epithelium of dromedary camels, alveolar epithelium of humans, and intestinal epithelium of common pipistrelle bats. In contrast, it does not bind to the nasal epithelium of pigs or rabbits, nor does it bind to the intestinal epithelium of serotine bats and frugivorous bat species. This finding supports the importance of the S1^A domain in MERS-CoV infection and tropism, suggests its role in transmission, and highlights its potential use as a component of novel vaccine candidates.

• Middle East respiratory syndrome coronavirus
• S1A domain
• common pipistrelle bats
• dromedary camels
• humans

•

The replication of S-intact PEDV was enhanced during coinfection with an S1 NTD-del PEDV in neonatal pigs.

Porcine epidemic diarrhea virus (PEDV) variants having a large deletion in the N-terminal domain of the S1 subunit of spike (S) protein were designated as S1 NTD-del PEDVs. They replicate well in experimentally infected pigs. However, on farms they often co-infect pigs with the PEDV containing an intact S protein (S-intact PEDV). We aimed to characterize viral replication and pathogenesis in neonatal gnotobiotic pigs infected simultaneously with the two types of PEDV using two recombinant PEDVs: icPC22A and its S1 NTD-del form icPC22A-S1Δ197. Additionally, viral replication was compared in Vero and IPEC-DQ cells at the presence of bovine mucin (BM), porcine gastric mucin (PGM), swine bile and bile acids during inoculation. In the pigs coinfected with icPC22A and icPC22A-S1Δ197, icPC22A replicated to a higher peak titer than its infection of pigs without the presence of icPC22A-S1Δ197. The severity of diarrhea and intestinal atrophy were similar between icPC22A and the coinfection groups, but were significantly higher than icPC22A-S1Δ197 group. In Vero and IPEC-DQ cells, certain concentrations of BM, PGM, bile and bile acids increased significantly the infectivity of icPC22A but had no or negative effects on icPC22A-S1Δ197. These results indicated that the replication of the S-intact PEDV was enhanced during coinfection in piglets. This observation may be explained partially by the fact that mucin, bile and bile acids in gastrointestinal tract had facilitating effects on the infection of S-intact PEDV, but no/inhibition effects on S1 NTD-del PEDV.

• Coinfection
• N-terminal domain
• Pathogenicity
• Porcine epidemic diarrhea virus
• S1 NTD-del
• Spike protein

Unlike for serotype II feline coronaviruses (FCoV II), the cellular receptor for serotype I FCoV (FCoV I), the most prevalent FCoV serotype, is unknown. To provide a platform for assessing the pattern by which FCoV I attaches to its host receptor(s), HEK293 cell lines that stably express the ectodomains of the spike (S) proteins derived from a FCoV I feline enteric coronavirus strain UU7 (FECV UU7) and a feline infectious peritonitis virus strain UU4 (FIPV UU4) were established. Using the recombinant S proteins as probes to perform S protein affinity histochemistry in paraffin‐embedded tissues, although no tissue or enteric binding of FECV UU7 S protein was detected, it was found that by immunohistochemistry that the tissue distribution of FIPV UU4 S protein‐bound cells correlated with that of FIPV antigen‐positive cells and lesions associated with FIP and that the affinity binding of FIPV UU4 S protein on macrophages was not affected by enzymatic removal of host cell‐surface sialic acid with neuraminidase. These findings suggest that a factor(s) other than sialic acid contribute(s) to the macrophage tropism of FIPV strain UU4. This approach allowed obtaining more information about both virus–host cell interactions and the biological characteristics of the unidentified cellular receptor for FCoV I.

• cell tropism
• feline infectious peritonitis virus
• histochemistry
• spike

• MERS-CoV
• attachment
• receptor
• sialic acid
• spike

Coronaviruses (CoVs) have a remarkable potential to change tropism. This is particularly illustrated over the last 15 years by the emergence of two zoonotic CoVs, the severe acute respiratory syndrome (SARS)- and Middle East respiratory syndrome (MERS)-CoV. Due to their inherent genetic variability, it is inevitable that new cross-species transmission events of these enveloped, positive-stranded RNA viruses will occur. Research into these medical and veterinary important pathogens—sparked by the SARS and MERS outbreaks—revealed important principles of inter- and intraspecies tropism changes. The primary determinant of CoV tropism is the viral spike (S) entry protein. Trimers of the S glycoproteins on the virion surface accommodate binding to a cell surface receptor and fusion of the viral and cellular membrane. Recently, high-resolution structures of two CoV S proteins have been elucidated by single-particle cryo-electron microscopy. Using this new structural insight, we review the changes in the S protein that relate to changes in virus tropism. Different concepts underlie these tropism changes at the cellular, tissue, and host species level, including the promiscuity or adaptability of S proteins to orthologous receptors, alterations in the proteolytic cleavage activation as well as changes in the S protein metastability. A thorough understanding of the key role of the S protein in CoV entry is critical to further our understanding of virus cross-species transmission and pathogenesis and for development of intervention strategies.

• Coronavirus spike
• Cross-species transmission
• Cryo-EM structure
• Membrane fusion
• Receptor interaction
• Tropism