Heterogeneity of swine lung macrophages inoculated by porcine reproductive and respiratory syndrome virus

Replication of Streptococcus equi subspecies zooepidemicus infection in swine

Streptococcus equi subspecies zooepidemicus (SEZ) is a commensal bacterium of horses and causes infections in mammalian species, including humans. Historically, virulent strains of SEZ caused high mortality in pigs in China and Indonesia, while disease in the U.S. was infrequent. More recently, high mortality events in sows were attributed to SEZ in North America. The SEZ isolates from these mortality events have high genetic similarity to an isolate from an outbreak in China. Taken together, this may indicate SEZ is an emerging threat to swine health. To generate a disease model and evaluate the susceptibility of healthy, conventionally raised pigs to SEZ, we challenged sows and five-month-old pigs with an isolate from a 2019 mortality event. Pigs were challenged with a genetically similar guinea pig isolate or genetically distinct horse isolate to evaluate comparative virulence. The swine isolate caused severe systemic disease in challenged pigs with 100 % mortality. Disease manifestation in sows was similar to field reports: lethargy/depression, fever, reluctance to rise, and high mortality. The guinea pig isolate also caused severe systemic disease; however, most five-month-old pigs recovered. In contrast, the horse isolate did not cause disease and was readily cleared from the respiratory tract. In conclusion, we were able to replicate disease reported in the field. The results indicate differences in virulence between isolates, with the highest virulence associated with the swine isolate. Additionally, we generated a challenge model that can be used in future research to evaluate virulence factors and disease prevention strategies.

Generation and Evaluation of a Glaesserella (Haemophilus) parasuis Capsular Mutant

Glaesserella (Haemophilus) parasuis is a commensal bacterium of the upper respiratory tract in pigs and also the causative agent of Glässer's disease, which causes significant morbidity and mortality in pigs worldwide. Isolates are characterized into 15 serovars by their capsular polysaccharide, which has shown a correlation with isolate pathogenicity. To investigate the role the capsule plays in G. parasuis virulence and host interaction, a capsule mutant of the serovar 5 strain HS069 was generated (HS069Δcap) through allelic exchange following natural transformation. HS069Δcap was unable to cause signs of systemic disease during a pig challenge study and had increased sensitivity to complement killing and phagocytosis by alveolar macrophages. Compared with the parent strain, HS069Δcap produced more robust biofilm and adhered equivalently to 3D4/31 cells; however, it was unable to persistently colonize the nasal cavity of inoculated pigs, with all pigs clearing HS069Δcap by 5 days postchallenge. Our results indicate the importance of the capsular polysaccharide to G. parasuis virulence as well as nasal colonization in pigs.

Heterogeneity and plasticity of porcine alveolar macrophage and pulmonary interstitial macrophage isolated from healthy pigs in vitro

This study investigated the heterogeneity and plasticity of porcine alveolar macrophages (PAM) and pulmonary interstitial macrophages (IM) isolated from healthy pigs, including phenotype, function and gene expression. Dynamic changes of nitric oxide (NO) levels secreted by PAM and IM with stimulation of different doses of lipopolysaccharide (LPS) were investigated by Griess method, and the viability of the PAM and IM cells was investigated by MTT assay. Flow cytometry, fluorescence quantitative PCR and ELISA techniques were used to measure cell phenotype, gene expression and cytokine secretion, respectively. The PAM and IM cells in normal healthy pigs showed heterogeneity with 95.42±1.51% and 31.99±5.84% of CD163+ macrophage, respectively. The NO level in IM was significantly higher versus PAM after LPS treatment. Consistently, the ratio of Arg I/iNOS in IM was much lower than that in PAM, suggesting that the PAM belong to M2 macrophages and the IM belong to M1 macrophages. The PAM and IM cells in normal healthy pigs also showed plasticity. The Arg I/iNOS ratio and TIMP1/MMP12 ratio were significantly decreased in LPS- or LPS+IFNγ-treated PAM and IM, suggesting that cells were polarized towards M1 macrophages under LPS or LPS+IFNγ stimulation. On the contrary, IL-4 and IL-13 stimulation on PAM and IM lead to M2 polarization. A similar result was found in IL-1β gene expression and TNFα secretion. In conclusion, porcine macrophages have shown heterogeneity and plasticity on polarization under the stimulation of LPS, IFNγ, IL-4 and IL-13.

Illumina MiSeq Sequencing Investigation of Microbiota in Bronchoalveolar Lavage Fluid and Cecum of the Swine Infected with PRRSV

Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant animal morbidity and mortality and economic losses worldwide. In this study, we analyzed the microbiota in bronchoalveolar lavage fluid (BAL), mucosa, and feces in cecum of the PRRSV-challenged pigs using the Illumina MiSeq sequencing platform, to investigate the role of microbiota in the pathogenesis and development of porcine reproductive and respiratory syndrome (PRRS). Quantitative insights into microbial ecology analyses indicated that the dominant bacterial groups in the lung from the PRRSV-challenged pigs were Haemophilus parasuis and Mycoplasma hyorhinis, with a relative abundance of 35-48% and 27-41%, respectively. Our results were consistent with the clinical observation that the PRRSV-infected pigs are always co-infected with other bacteria, such as Haemophilus and Mycoplasma. On the other hand, Campylobacter and Clostridium became the two most abundant bacteria in the mucosal and luminal microbiota of the cecum of the PRRSV-challenged pigs, and the relative abundance was four times higher than that in the healthy pigs. This suggested that Campylobacter and Clostridium might be associated with the pathogenesis of diarrhea in PRRS. Linear discriminant analysis effect size reveals significant microbial dysbiosis of BAL, mucosa, and feces in cecum of the PRRSV-challenged pigs. We have identified a structural imbalance of the microbiota, characterized by a reduced diversity of microbiota and abundance alterations of certain bacteria in the PRRSV-challenged pigs. The observed microbiota dysbiosis in this study provides insight into the roles of the microbiota in the complications of the PRRSV infection.