Double-stranded RNA (dsRNA) and its mimic, polyinosinic acid: polycytidylic acid [Poly (I:C)], are recognized by toll-like receptor 3 (TLR3) and induce interferon (IFN)-β in many cell types. Poly (I:C) is the most potent IFN inducer. In in vivo mouse studies, intraperitoneal injection of Poly (I:C) elicited IFN-α/β production and natural killer (NK) cells activation. The TLR3 pathway is suggested to contribute to innate immune responses against many viruses, including influenza virus, respiratory syncytial virus, herpes simplex virus 2, and murine cytomegalovirus. In Chikungunya virus (CHIKV) infection, the viruses are cleared within 7–10 days postinfection before adaptive immune responses emerge. The innate immune response is important for CHIKV clearance.

Outbreaks of a new variant of porcine epidemic diarrhea virus (PEDV) at the end of 2010 have raised interest in the mutation and recombination of PEDV. A PEDV strain (CN/Liaoning25/2018) isolated from a clinical outbreak of piglet diarrhea contained a 49-bp deletion in the ORF3 gene. This deletion is considered a genetic characteristic of low pathogenic attenuated vaccine strains. However, CN/Liaoning25/2018 was highly pathogenic. Complete genome sequencing, identity analysis, phylogenetic tree construction, and recombination analysis showed that this virus was a recombinant strain containing the Spike (S) gene from the highly pathogenic CN/GDZQ/2014 strain and the remaining genomic regions from the low pathogenic vaccine isolate SQ2014. Histopathology and immunohistochemistry results confirmed that this strain was highly pathogenic and indicated that intestinal epithelial cell vacuolation was positively correlated with the intensity and density of PEDV antigens. A new natural recombination model for PEDV was identified. Our results suggest that new highly pathogenic recombinant strains in the field may be generated by recombination between low pathogenic attenuated live PEDV vaccines and pathogenic circulating PEDV strains. Our findings also highlight that the 49-bp deletion of the ORF3 gene in low pathogenic attenuated vaccine strains will no longer be a reliable standard to differentiate the classical vaccine attenuated from the field strains.

Objectives: Chikungunya virus (CHIKV) is an alphavirus belonging to the Togaviridae family. Alphaviruses cause a chronic non-cytopathic infection in mosquito cells, while they develop a highly cytopathic infection in cells originating from various vertebrates. In this study, we compared the cytopathic effect (CPE) induced by CHIKV in Vero cells and a mosquito cell line, C6/36 cells. Methods: CPE and the virus titers were compared between the CHIKV-infected C6/36 and Vero cells. Apoptosis was measured by TUNEL assay, and the differences between the C6/36 and Vero cells were compared. Results: CHIKV infection induced strong CPE and apoptosis in the Vero cells, but light CPE in the C6/36 cells. The virus titers produced in the C6/36 cells were much higher than those produced in the Vero cells. Conclusions: The reason CHIKV induced strong CPE is that this virus triggers strong apoptosis in Vero cells compared with C6/36 cells. CHIKV established a persistent infection in C6/36 cells after being passaged 20 times. CHIKV infection in mosquito cells was distinct from that in Vero cells. The cell and species specificity of CHIKV-induced cell death implies that the cellular and viral regulators involved in apoptosis may play an important role in determining the outcome of CHIKV infection.

Background: Rotavirus (RV) is a principal cause of diarrhea. However, there is a limited understanding regarding alteration of the gut microbial community structure and abundance during RV infection. This study was to characterize any potential associations between RV infection and the intestinal microbiota. Methods: Suckling mice were divided into normal group (NC) and infected group (RV) randomly. All of the suckling mice were euthanized four days post-RV infection. The virus titer was counted as fluorescent focus assay, and viral load was quantified by QPCR. Five sucking mice were randomly selected from each RV group and NC group for sample collection and pathological analysis. Mixed intestinal contents of the colon and rectum were collected from all of the suckling mice. To investigate the detailed relationship between RV infection and intestinal microbiota, the composition and distribution of intestinal microbiota from suckling mice were first analyzed using 16S rRNA sequencing technology. Results: The results of the pathological characteristics showed that vacuolar degeneration, vasodilation, hyperemia, and destruction of the intestinal epithelium were apparent in the RV group. Representative genera from Lactobacillus and Fusobacterium were enriched in the NC group, while the Enterococcus and Escherichia/Shigella genera were enriched in the RV group. Helicobacter, Alloprevotrlla, Brevundimonas, Paenibacillus, and Parabacteroides were completely undetectable in the RV group. The predicted intestinal flora metabolic function results showed that “carbohydrate metabolism” and “lipid metabolism” pathways were significantly enriched within the NC group. A significant difference has been observed in the gut microbiota composition between the two groups. Conclusions: Our results demonstrated a significant difference in the gut microbiota composition in RV-infected suckling mice as compared to the RV un-infected suckling mice group. This work may provide meaningful information regarding the bacterial genera changed during RV infection. Moreover, the changes in these bacteria may be related with the replication and pathogenesis of RV infection.

Porphyromonas gingivalis (P. gingivalis) is a periodontal pathogen that may accumulate with other organisms in subgingival plaque biofilms and is associated with periodontal disease. P. gingivalis fimbriae (FimA) is a filamentous structure on the surface of bacteria that is closely associated with bacterial adhesion to and colonization of host tissues, and serves an essential role in biofilm formation. The present study aimed to construct P. gingivalis FimA prokaryotic expression plasmids, purify a FimA fusion protein and explore the effect of a recombinant FimA protein on the inflammatory response in human peripheral blood mononuclear cells (PBMCs). P. gingivalis FimA prokaryotic expression plasmids were constructed by gene cloning and recombination technology. SDS‑PAGE was used to evaluate the purified recombinant FimA protein. The cell proliferation rate and inflammatory cytokine expression of PBMCs treated with the FimA fusion protein with or without transfection with toll‑like receptor 4 (TLR4) small interfering (si)RNA were detected by CCK‑8 assays and ELISAs, respectively. The expression levels of TLR4, nuclear factor kappa‑light‑chain‑enhancer of activated B cells (NF‑κB) and myeloid differentiation primary response 88 (MyD88) in PBMCs were detected by western blot analysis and reverse transcription quantitative polymerase chain reaction. A FimA fusion protein with high purity was obtained. FimA fusion protein treatment significantly increased PBMC proliferation and promoted the release of tumor necrosis factor‑α (TNF‑α), interleukin (IL)‑6, matrix metalloproteinase (MMP)‑8 and MMP‑9 in PBMCs. TLR4 interference reversed the effects of the FimA fusion protein on PBMC proliferation and inflammatory cytokine release. The expression levels of TLR4, NF‑κB and MyD88 in PBMCs were significantly increased following treatment with the FimA fusion protein, while the expression levels of these genes at the mRNA and protein levels decreased significantly in PBMCs following FimA fusion protein treatment and TLR4 interference. The FimA fusion protein increased PBMC proliferation and promoted the release of the inflammatory cytokines TNF‑α, IL‑6, MMP‑8 and MMP‑9 via the TLR4/NF‑κB signaling pathway. FimA may serve as a promising therapeutic strategy for periodontal disease.