Isolation and development of bovine primary respiratory cells as model to study influenza D virus infection

Influenza D virus (IDV) is a novel type of influenza virus that infects and causes respiratory illness in bovines. Lack of host-specific in vitro model that can recapitulate morphology and physiology of in vivo airway epithelial cells has impeded the study of IDV infection. Here, we established and characterized bovine primary respiratory epithelial cells from nasal turbinate, soft palate, and trachea of the same calf. All three cell types showed characteristics peculiar of epithelial cells, polarized into apical-basolateral membrane, and formed tight junctions. Furthermore, these cells expressed both α-2,3- and α-2,6-linked sialic acids with α-2,3 linkage being more abundant. IDV strains replicated to high titers in these cells, while influenza A and B viruses exhibited moderate to low titers, with influenza C virus replication not detected. These findings suggest that bovine primary airway epithelial cells can be utilized to model infection biology and pathophysiology of IDV and other respiratory pathogens.

Proteogenomics Uncovers Critical Elements of Host Response in Bovine Soft Palate Epithelial Cells Following In Vitro Infection with Foot-And-Mouth Disease Virus

Foot-and-mouth disease (FMD) is the most devastating disease of cloven-hoofed livestock, with a crippling economic burden in endemic areas and immense costs associated with outbreaks in free countries. Foot-and-mouth disease virus (FMDV), a picornavirus, will spread rapidly in naïve populations, reaching morbidity rates of up to 100% in cattle. Even after recovery, over 50% of cattle remain subclinically infected and infectious virus can be recovered from the nasopharynx. The pathogen and host factors that contribute to FMDV persistence are currently not understood. Using for the first time primary bovine soft palate multilayers in combination with proteogenomics, we analyzed the transcriptional responses during acute and persistent FMDV infection. During the acute phase viral RNA and protein was detectable in large quantities and in response hundreds of interferon-stimulated genes (ISG) were overexpressed, mediating antiviral activity and apoptosis. Although the number of pro-apoptotic ISGs and the extent of their regulation decreased during persistence, some ISGs with antiviral activity were still highly expressed at that stage. This indicates a long-lasting but ultimately ineffective stimulation of ISGs during FMDV persistence. Furthermore, downregulation of relevant genes suggests an interference with the extracellular matrix that may contribute to the skewed virus-host equilibrium in soft palate epithelial cells.

Quantitative analysis of foot-and-mouth disease virus RNA loads in bovine tissues: implications for the site of viral persistence

To understand better the pathogenesis of foot-and-mouth disease (FMD), the levels of viral RNA in various bovine tissues during the acute and persistent stages of FMD virus (FMDV) infection were investigated by using quantitative RT-PCR. The viral RNA levels in the tissues examined had peaked by day 1 post-infection (p.i.) and were markedly different among the tissues examined. The epithelium collected from sites of lesion development, i.e. the interdigital area and coronary band on the feet, and the tongue, contained the highest level of viral RNA, indicating the predominant tissue sites of viral infection and amplification during the acute stage of infection. Clearance of viral RNA from most of the tissues occurred relatively rapidly and the rate of clearance was largely independent of the level of viral RNA. The viral RNA load in most of the tissues declined slower than in serum, in which viral clearance is rapid. Beyond 28 days p.i., a proportion of pharyngeal region tissues (soft palate, pharynx, tonsil and mandibular lymph node) from infected animals still contained a detectable level of viral RNA, while viral RNA in non-pharyngeal region tissues was generally only detectable for variable periods ranging from 4 to 14 days p.i. The presence of viral RNA in dorsal soft palate tissue had a good correlation with the presence of infectious virus in oesophageal-pharyngeal fluid (OP-fluid) samples, a finding indicative of the specific tissue sites of FMDV persistence.

The localization of persistent foot and mouth disease virus in the epithelial cells of the soft palate and pharynx

After contact with foot and mouth disease virus (FMDV), cattle may become persistently infected, regardless of their pre-existing immune status or whether they develop clinical disease. The cellular sites of FMDV persistence have not previously been determined. The use of in-situ hybridization in combination with tyramide signal amplification (TSA) provided the first direct evidence that FMDV RNA is localized within the epithelial cells of the soft palate and pharynx during persistent infection, indicating that these cells remain persistently infected after contact with FMDV.

[The pathogenicity of HFRS patient's soft palate mucosa to suckling mice]

OBJECTIVE

To explore the pathogenic mechanism of hemorrhagic fever with renal syndrome(HFRS).

METHODS

2-3 days old inbred Balb/C suckling mice were inoculated intracerebrally with tissue suspension of soft palate petechia of HFRS patients and the HFRS virus RNA was tested in brain, lung and kidney tissues of sucking mice by nested PCR.

RESULTS

Some of the mice developed acute disease and died. The autopsy analysis indicated that these mice showed pathological changes in microvascular system and parenchymatous tissues. HFRS virus RNA was detected in their brains, lungs and kidney tissues.

CONCLUSIONS

These results indicate that HFRS virus exists in the tissue of petechial hemorrhagic spots on soft palate petechia of HFRS patients.

Transmission electron microscopic study of the hemorrhagic spots in patients with epidemic hemorrhagic fever in the early stage

Epidemic hemorrhagic fever (EHF) virus particles were found in the squamous epithelial cells and the capillary endothelial cells of the petechial spots located on the mucous membrane of the soft palate in 3 patients with severe early-stage EHF with transmission electron microscopy. The virus particles were round or oval in shape, about 100 nm in diameter, with a two-layer lipid envelope from which spikes were protruding. The nucleocapsid of the virus appeared to be hollow microfilamentoid or dense granules. Meanwhile, budding virus particles with a diameter of 80 nm were found in the enlarged Golgi apparatus. The infected cells displayed an enlarged and proliferating Golgi apparatus. The morphological characteristics of the viron mentioned above coincided with those of the virus particles of the family Bunyaviridae. This study is the first to demonstrate that the squamous epithelial cells on the mucous membrane of the soft palate are the target cells of EHF infection and to provide subcellular morphological evidence of petechial hemorrhage at the soft palate.

Immunohistochemical detection of rinderpest virus: effects of autolysis and period of fixation

Samples of eyelid, tongue, soft palate and palatine tonsil were collected from calves infected experimentally with rinderpest virus. The tissues were fixed in 10 per cent neutral buffered formalin immediately, 24 or 48 hours post mortem. Then, after three days, 10 days, 28 days or three months in formalin, they were processed into paraffin blocks and examined immunohistochemically for rinderpest viral antigen. The tonsil was the best of the four tissues in providing a consistently positive immunohistochemical signal for the presence of virus, despite autolytic changes and/or prolonged fixation.

Optimization of an in situ hybridization technique for the detection of foot-and-mouth disease virus in bovine tissues using the digoxigenin system

An in situ hybridization technique has been optimised for use on paraffin-embedded sections of tissues collected from cattle infected experimentally with foot-and-mouth disease virus type O1BFS. Tissue was collected 5 days after infection by direct contact. In situ hybridization was carried out using an RNA probe corresponding to a region of the 3D gene which codes for the RNA polymerase, and labelled with digoxigenin. Consistent, reproducible signal was detected within the epithelial layers of the palatine tonsil, soft palate and pharyngeal tissue studied. This is the first time that a digoxigenin-based system has been used successfully for FMD virus RNA detection with bovine tissue samples.

Improved detection of persistent foot-and-mouth disease infection in cattle by the polymerase chain reaction

Persistent foot-and-mouth disease (FMD) infection of cattle was established by exposure to infected pigs. Oesophageal-pharyngeal fluid samples collected ante-mortem and tissue samples obtained post-mortem were tested for virus by conventional means and for viral RNA by the polymerase chain reaction (PCR). The results showed that the PCR was superior for detecting the carrier state in tissue samples. A high neutralising activity in tissues probably influenced the yields of virus obtained by infectivity assay.