Interleukin-17A Contributed to the Damage of Blood-CNS Barriers During Streptococcus suis Meningitis.

Streptococcus suis (S. suis) is an emerging zoonotic agent that can cause meningitis in humans with high mortality and morbidity. Meningitic S. suis can induce higher level of IL-17 than non-meningitic S. suis. Besides, IL-17A plays various roles on bacterial clearance or disruption of blood-CNS barriers through the downregulation and reorganization of tight junction (TJ) molecules. However, it remains to be elucidated for the role of IL-17A on the infection with meningitic S. suis. Here, we found that meningitic S. suis infection could not only cause acute death due to the damage of multiple organs, but also cause meningitis and clinical nervous signs since 60 h of post-infection due to the penetration of blood-CNS barriers after lasting bacteremia. In contrast, the mice with deficiency of il17a gene could not significantly change the acute inflammatory response and acute death, but it could not show obvious meningitis and clinical nervous signs caused by the meningitic S. suis infection. In addition, we also found that IL-17A could inhibit the transcription and expression of TJ proteins that facilitated the leakage of blood-CNS barriers since 60 h of post-infection during meningitic S. suis infection. Thus, our findings demonstrated that IL-17A could downregulate TJ proteins, which undoubtedly facilitated the leakage of blood-CNS barriers for bacterial invasion and then caused S. suis meningitis, providing potential targets for future prevention and treatment of this disease.

Interleukin-17A Contributes to Bacterial Clearance in a Mouse Model of Streptococcal Toxic Shock-Like Syndrome.

Streptococcus suis (S. suis), an emerging zoonotic pathogen, can cause streptococcal toxic shock-like syndrome (STSLS) in humans with high mortality. STSLS is characterized by high bacterial burden, an inflammatory cytokine storm, multi-organ dysfunction, and ultimately acute host death. Although it has been found that a significantly high level of IL-17A was induced in an NLRP3-dependent manner during STSLS development, the role of IL-17A on S. suis STSLS remains to be elucidated. In this study, we found that the epidemic strain SC 19 caused a significantly higher level of IL-17A than the non-epidemic strain P1/7. In addition, higher bacterial burden was observed from SC 19-infected il17a-/- mice than il17a+/+ mice, although acute death, tissue injury and inflammatory cytokines storm were observed in both types of mice. Furthermore, compared with il17a+/+ mice, the level of neutrophils recruitment was lower in il17a-/- mice, and the levels of induced antimicrobial proteins, such as CRAMP, S100A8 and lipocalin-2, were also decreased in il17a-/- mice. In conclusion, this study demonstrated that IL-17A does not contribute to the severe inflammation, although it may play a minor role for bacterial clearance by inducing antimicrobial proteins and promoting neutrophil recruitment during STSLS.

Acquiring high expression of suilysin enable non-epidemic Streptococccus suis to cause streptococcal toxic shock-like syndrome (STSLS) through NLRP3 inflammasome hyperactivation.

The epidemic Streptococcus suis (S. suis) strain [Sequence type (ST) 7] was gradually evolving from the non-epidemic ST1 strain and got the ability for high expressing of suilysin (SLY). And the high expression of SLY was required for the epidemic strain to cause NLRP3 hyperactivation, which is essential for the induction of cytokines storm, dysfunction of multiple organs, and a high incidence of mortality, the characters of streptococcal toxic shock-like syndrome (STSLS). However, it remains to be elucidated whether acquiring high SLY expression due to genome evolution was sufficient for the non-epidemic strain to cause STSLS. Here, we found that the overexpression of SLY in ST1 strain (P1/7-SLY) could obviously increase the inflammasome activation, which was dependent on NLRP3 signalling. In contrast, the strain (P1/7-mSLY) overexpressing the mutant SLY (protein without hemolytic activity) could not significantly increase the inflammasome activation. Furthermore, similar to the epidemic strain, P1/7-SLY could cause STSLS in nlrp3+/+ mice but not in nlrp3-/- mice. In contrast, P1/7-mSLY could not cause STSLS in both nlrp3 +/+ mice and nlrp3-/- mice. In summary, we demonstrate that genetic evolution enabling S. suis strain to express high level of SLY may be an essential and sufficient condition for NLRP3 inflammasome hyperactivation, which could further cause cytokines storm and STSLS.

Isolation and genetic characteristics of a neurotropic teschovirus variant belonging to genotype 1 in northeast China.

Porcine teschovirus (PTV) is a causative agent of reproductive disorders, encephalomyelitis, respiratory diseases, and diarrhea in swine, with a worldwide distribution. In this work, we identified PTV-associated nonsuppurative encephalitis as a potential cause of posterior paralysis in neonatal pigs in northeast China. Using indirect immunofluorescence assay, western blot, electron microscopy, and genome sequencing, we identified a neurotropic PTV strain, named CHN-NP1-2016, in the supernatants of pooled cerebrum and cerebellum samples from an affected piglet. Nucleotide sequence alignment revealed that the whole genome of CHN-NP1-2016 shared the highest sequence similarity (86.76% identity) with PTV 1 strain Talfan. A combination of phylogenetic and genetic divergence analysis was applied based on the deduced amino acid sequence of the P1 gene with a cutoff value of the genetic distance (0.102 ± 0.008) for defining PTV genotypes, and this showed that CHN-NP1-2016 is a variant of genotype 1. In total, 16 unique mutations and five mutant clusters were detected in the capsid proteins VP1 and VP2 of CHN-NP1-2016 when compared to other PTV1 isolates. Importantly, we detected three mutant clusters located in the exposed surface loops of the capsid protein, potentially indicating significant differences in major neutralization epitopes. Moreover, a potential recombination event in the P1 region of PTV CHN-NP1-2016 was detected. These findings provide valuable insights into the role of recombination in the evolution of teschoviruses. To our knowledge, this is the first case report of PTV-1-associated encephalitis in northeast China. Future investigations will narrow on the serology and pathogenicity of this novel isolate.

Porcine Epidemic Diarrhea Virus Induces Autophagy to Benefit Its Replication.

The new porcine epidemic diarrhea (PED) has caused devastating economic losses to the swine industry worldwide. Despite extensive research on the relationship between autophagy and virus infection, the concrete role of autophagy in porcine epidemic diarrhea virus (PEDV) infection has not been reported. In this study, autophagy was demonstrated to be triggered by the effective replication of PEDV through transmission electron microscopy, confocal microscopy, and Western blot analysis. Moreover, autophagy was confirmed to benefit PEDV replication by using autophagy regulators and RNA interference. Furthermore, autophagy might be associated with the expression of inflammatory cytokines and have a positive feedback loop with the NF-κB signaling pathway during PEDV infection. This work is the first attempt to explore the complex interplay between autophagy and PEDV infection. Our findings might accelerate our understanding of the pathogenesis of PEDV infection and provide new insights into the development of effective therapeutic strategies.

Comparative Proteome Analysis of Porcine Jejunum Tissues in Response to a Virulent Strain of Porcine Epidemic Diarrhea Virus and Its Attenuated Strain.

Porcine epidemic diarrhea virus (PEDV), a predominant cause of acute enteric infection, leads to severe dehydrating diarrhea and mortality in piglets all over the world. A virulent PEDV YN13 strain, isolated in our laboratory, was attenuated to yield an attenuated PEDV strain YN144. To better understand the pathogenesis mechanism and the virus-host interaction during infection with both PEDV YN13 and YN144 strains, a comparative proteomic analysis was carried out to investigate the proteomic changes produced in the primary target organ, using isobaric tags for relative and absolute quantitation (iTRAQ) labeling, followed by liquid chromatography tandem-mass spectrometry (LC-MS/MS). A total of 269 and 301 differently expressed proteins (DEPs) were identified in the jejunum tissues of the piglets inoculated with YN13 and YN144, respectively. Bioinformatics analysis revealed that these proteins were involved in stress responses, signal transduction, and the immune system. All of these involved interferon-stimulated genes (ISGs) which were up-regulated in jejunums by both of the PEDV-infected groups. Based on the comparative analysis, we proposed that different changes induced by YN13 and YN144 in heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), eukaryotic initiation factor 4G1 (eIF4G1), and some members in the heat shock protein (HSP) family, may be responsible for differences in their pathogenicity.

Comparative Genomic Analysis of Classical and Variant Virulent Parental/Attenuated Strains of Porcine Epidemic Diarrhea Virus.

Since 2010, the variant porcine epidemic diarrhea virus (PEDV) has been the etiological agent responsible for the outbreak of porcine epidemic diarrhea (PED) worldwide. In this study, a variant PEDV strain YN1 was isolated, serially propagated on the Vero cells and was characterized for 200 passages. To better elucidate the molecular basis of Vero cell adaptation of variant PEDV strains, we sequenced, compared, and analyzed the full-genome sequences of parental YN1 and passages 15, 30, 60, 90, 144, and 200. The results showed that the variations increased with the viral passage. The nucleotides sequences of non-structural protein (NSP)2, NSP4-7, NSP10, NSP12 and NSP13 genes did not change during the Vero cell adaptation process. After comparison of the variation characteristic of classical, variant virulent/attenuated strains, it was found that attenuation of PEDV virus was associated with 9-26 amino acid (aa) changes in open reading frames (ORF) 1a/b and S protein, early termination in ORF3, 1-3 aa changes in E, M and N protein and some nucleotide sequences' synonymous mutations. The aa deletion at about 144 aa of S protein could be the attenuation marker for the PEDV. The pig study showed that the early termination in ORF3 was more important for virus cell adaptation than virus attenuation.

Full-Length Genome Characterization of Chinese Porcine Deltacoronavirus Strain CH/SXD1/2015.

A porcine deltacoronavirus (PDCoV) was identified in the Chinese mainland and found to be closely related to Hong Kong strain HKU15-155 but differed from PDCoV strains in the United States and South Korea. The complete genome of PDCoV strain CH/SXD1/201 was sequenced and analyzed to further characterize PDCoV in Chinese swine.