Unique Tropism and Entry Mechanism of Mumps Virus

Mumps virus (MuV) is an important human pathogen that causes parotitis, orchitis, oophoritis, meningitis, encephalitis, and sensorineural hearing loss. Although mumps is a vaccine-preventable disease, sporadic outbreaks have occurred worldwide, even in highly vaccinated populations. MuV not only causes systemic infection but also has a unique tropism to glandular tissues and the central nervous system. In general, tropism can be defined by multiple factors in the viral life cycle, including its entry, interaction with host factors, and host-cell immune responses. Although the underlying mechanisms of MuV tropism remain to be fully understood, recent studies on virus-host interactions have provided insights into viral pathogenesis. This review was aimed at summarizing the entry process of MuV by focusing on the glycan receptors, particularly the recently identified receptors with a trisaccharide core motif, and their interactions with the viral attachment proteins. Here, we describe the receptor structures, their distribution in the human body, and the recently identified host factors for MuV and analyze their relationship with MuV tropism.

Comparable Infection Level and Tropism of Measles Virus and Canine Distemper Virus in Organotypic Brain Slice Cultures Obtained from Natural Host Species

Measles virus (MV) and canine distemper virus (CDV) are closely related members of the family Paramyxoviridae, genus Morbillivirus. MV infection of humans and non-human primates (NHPs) results in a self-limiting disease, which rarely involves central nervous system (CNS) complications. In contrast, infection of carnivores with CDV usually results in severe disease, in which CNS complications are common and the case-fatality rate is high. To compare the neurovirulence and neurotropism of MV and CDV, we established a short-term organotypic brain slice culture system of the olfactory bulb, hippocampus, or cortex obtained from NHPs, dogs, and ferrets. Slices were inoculated ex vivo with wild-type-based recombinant CDV or MV expressing a fluorescent reporter protein. The infection level of both morbilliviruses was determined at different times post-infection. We observed equivalent infection levels and identified microglia as main target cells in CDV-inoculated carnivore and MV-inoculated NHP brain tissue slices. Neurons were also susceptible to MV infection in NHP brain slice cultures. Our findings suggest that MV and CDV have comparable neurotropism and intrinsic capacity to infect CNS-resident cells of their natural host species.

Age-Associated Changes in Recombinant H5 Highly Pathogenic and Low Pathogenic Avian Influenza Hemagglutinin Tissue Binding in Domestic Poultry Species

The 2014 outbreak of clade 2.3.4.4A highly pathogenic avian influenza (HPAI) led to the culling of millions of commercial chickens and turkeys and death of various wild bird species. In this outbreak, older chickens and turkeys were commonly infected, and succumbed to clinical disease compared to younger aged birds such chicken broilers. Some experimental studies using waterfowl species have shown age-related differences in susceptibility to clinical disease with HPAI viruses. Here, we evaluate differences in H5 Hemagglutinin (HA) tissue binding across age groups, using recombinant H5 HA (rHA) proteins generated using gene sequences from low pathogenic (A/mallard/MN/410/2000(H5N2 (LPAIV)) and a HPAIV (A/Northern pintail/Washington/40964/2014(H5N2)) influenza A virus (IAV). Respiratory and intestinal tracts from chickens, ducks (Mallard, Pekin, Muscovy) and turkeys of different age groups were used to detect rHA binding with protein histochemistry, which was quantified as the median area of binding (MAB) used for statistical analysis. There were species and tissue specific differences in the rHA binding among the age groups; however, turkeys had significant differences in the HPAIV rHA binding in the respiratory tract, with younger turkeys having higher levels of binding in the lung compared to the older group. In addition, in the intestinal tract, younger turkeys had higher levels of binding compared to the older birds. Using LPAIV, similar species and tissues, specific differences were seen among the age groups; however, only turkeys had overall significant differences in the respiratory tract MAB, with the older birds having higher levels of binding compared to the younger group. No age-related differences were seen in the overall intestinal tract rHA binding. Age-related differences in rHA binding of the LPAIV and HPAIV demonstrated in this study may partially, but not completely, explain differences in host susceptibility to infection observed during avian influenza outbreaks and in experimental infection studies.

Respiratory Tract Explant Infection Dynamics of Influenza A Virus in California Sea Lions, Northern Elephant Seals, and Rhesus Macaques

To understand susceptibility of wild California sea lions and Northern elephant seals to influenza A virus (IAV), we developed an ex vivo respiratory explant model and used it to compare infection kinetics for multiple IAV subtypes. We first established the approach using explants from colonized rhesus macaques, a model for human IAV. Trachea, bronchi, and lungs from 11 California sea lions, 2 Northern elephant seals, and 10 rhesus macaques were inoculated within 24 h postmortem with 6 strains representing 4 IAV subtypes. Explants from the 3 species showed similar IAV infection kinetics, with peak viral titers 48 to 72 h post-inoculation that increased by 2 to 4 log₁₀ PFU/explant relative to the inoculum. Immunohistochemistry localized IAV infection to apical epithelial cells. These results demonstrate that respiratory tissue explants from wild marine mammals support IAV infection. In the absence of the ability to perform experimental infections of marine mammals, this ex vivo culture of respiratory tissues mirrors the in vivo environment and serves as a tool to study IAV susceptibility, host range, and tissue tropism.

IMPORTANCE Although influenza A virus can infect marine mammals, a dearth of marine mammal cell lines and ethical and logistical challenges prohibiting experimental infections of living marine mammals mean that little is known about IAV infection kinetics in these species. We circumvented these limitations by adapting a respiratory tract explant model first to establish the approach with rhesus macaques and then for use with explants from wild marine mammals euthanized for nonrespiratory medical conditions. We observed that multiple strains representing 4 IAV subtypes infected trachea, bronchi, and lungs of macaques and marine mammals with variable peak titers and kinetics. This ex vivo model can define infection dynamics for IAV in marine mammals. Further, use of explants from animals euthanized for other reasons reduces use of animals in research.

The Human Cytomegalovirus Protein UL116 Interacts with the Viral Endoplasmic-Reticulum-Resident Glycoprotein UL148 and Promotes the Incorporation of gH/gL Complexes into Virions

Heterodimers of glycoproteins H (gH) and L (gL) comprise a basal element of the viral membrane fusion machinery conserved across herpesviruses. In human cytomegalovirus (HCMV), the glycoprotein UL116 assembles onto gH at a position similar to that occupied by gL, forming a heterodimer that is incorporated into virions. Here, we show that UL116 promotes the expression of gH/gL complexes and is required for the efficient production of infectious cell-free virions. UL116-null mutants show a 10-fold defect in production of infectious cell-free virions from infected fibroblasts and epithelial cells. This defect is accompanied by reduced expression of two disulfide-linked gH/gL complexes that play crucial roles in viral entry: the heterotrimer of gH/gL with glycoprotein O (gO) and the pentameric complex of gH/gL with UL128, UL130, and UL131. Kifunensine, a mannosidase inhibitor that interferes with endoplasmic reticulum (ER)-associated degradation (ERAD) of terminally misfolded glycoproteins, restored levels of gH, gL, and gO in UL116-null-infected cells, indicating that constituents of HCMV gH complexes are unstable in the absence of UL116. Further, we find that gH/UL116 complexes are abundant in virions, since a major gH species not covalently linked to other glycoproteins, which has long been observed in the literature, is detected from wild-type but not UL116-null virions. Interestingly, UL116 coimmunoprecipitates with UL148, a viral ER-resident glycoprotein that attenuates ERAD of gO, and we observe elevated levels of UL116 in UL148-null virions. Collectively, our findings argue that UL116 is a chaperone for gH that supports the assembly, maturation, and incorporation of gH/gL complexes into virions. IMPORTANCE HCMV is a betaherpesvirus that causes dangerous opportunistic infections in immunocompromised patients as well as in the immune-naive fetus and preterm infants. The potential of the virus to enter new host cells is governed in large part by two alternative viral glycoprotein H (gH)/glycoprotein L (gL) complexes that play important roles in entry: gH/gL/gO and gH/gL/UL128-131. A recently identified virion gH complex, comprised of gH bound to UL116, adds a new layer of complexity to the mechanisms that contribute to HCMV infectivity. Here, we show that UL116 promotes the expression of gH/gL complexes and that UL116 interacts with the viral ER-resident glycoprotein UL148, a factor that supports the expression of gH/gL/gO. Overall, our results suggest that UL116 is a chaperone for gH. These findings have important implications for understanding HCMV cell tropism as well as for the development of vaccines against the virus.

mSphere of Influence: Forgotten Questions

Laura-Isobel McCall studies the relationship between location and disease pathogenesis, with a focus on infectious diseases and neglected diseases of poverty. In this mSphere of Influence article, she reflects on how three papers, "Opposing effects of fasting metabolism on tissue tolerance in bacterial and viral inflammation" (A. Wang, S. C. Huen, H. H. Luan, S. Yu, et al., Cell 166:1512-1525.e12, 2016, https://doi.org/10.1016/j.cell.2016.07.026), "Three-dimensional microbiome and metabolome cartography of a diseased human lung" (N. Garg, M. Wang, E. Hyde, R. R. da Silva, et al., Cell Host Microbe 22:705-716.e4, 2017, https://doi.org/10.1016/j.chom.2017.10.001), and "'It's like a phantom disease': patient perspectives on access to treatment for Chagas disease in the United States" (C. J. Forsyth, S. Hernandez, C. A. Flores, M. F. Roman, et al., Am J Trop Med Hyg 98:735-741, 2018, https://doi.org/10.4269/ajtmh.17-0691), shaped her spatial approach to infectious disease pathogenesis and helped her broaden her perspective from a pathogen-centric focus to a holistic view that include diseases tolerance mechanisms and barriers to health care access.

Sacralization may be associated with facet orientation and tropism but not degenerative changes of the lumbar vertebrae

Purpose

In this retrospective study, we aimed to investigate the possible effects of transitional vertebra anatomy on facet joint tropism and orientation by evaluating lumbar magnetic resonance imaging (MRI) studies performed at our institution.

Material and methods

We included 84 patients with sacralization of the L5 vertebra and an equal number of patients with a radiology report within normal limits as the control group in our study. We compared facet tropism (FT) and orientation between both groups.

Results

In both the sacralization group and the control group, the facet orientation angle showed a significant increasing trend from the L1-L2 level to the L5-S1 level (p < 0.001). The orientation angle of the L5-S1 level was higher in the sacralization group compared to the control group (p < 0.01). In the evaluation of FJ orientation between the sacralization and control groups, we found that coronal orientation was significantly more frequent at the L5-S1 level in the sacralization group. When the 2 groups were compared with regard to tropism at each spinal level, the sacralization group had a significantly higher FT frequency at the L5-S1 level (p < 0.001).

Conclusions

To our knowledge, this is the first study to evaluate the relationship between sacralization and facet joint tropism. However, there were no relationships between facet degeneration, disc degeneration/herniation, and sacralization. Our results indicate that, although patients with sacralization and controls had similar characteristics in most assessments, they demonstrated significant differences at the L5-S1 level in terms of orientation and tropism.

Innate Lymphoid Cells in Tissue Homeostasis and Disease Pathogenesis

Innate lymphoid cells (ILCs) are the most recently discovered family of innate immune cells. ILCs can be categorized into three groups on the basis of the transcription factors that direct their functions and the cytokines they produce. Notably, these functions parallel the effector functions of T lymphocytes. ILCs play a frontline role in host defense and tissue homeostasis by responding rapidly to environmental factors, conducting effector responses in a tissue-specific manner, and interacting with hematopoietic and non-hematopoietic cells throughout the body. Moreover, recent studies reveal that ILCs are involved in development of various inflammatory diseases, such as respiratory diseases, autoimmune diseases, or cancer. In this review, we discuss the recent findings regarding the biology of ILCs in health and inflammatory diseases.

A(H1N1)pdm09 influenza viruses replicating in ferret upper or lower respiratory tract differed in onward transmission potential by air

BACKGROUND

A(H1N1)pdm09 influenza viruses replicate efficiently in respiratory epithelia and are transmitted via respiratory droplets and aerosols expelled by infected hosts. The relative onward transmission potential of influenza viruses replicating in the upper and lower respiratory epithelial cells has not been fully defined.

METHODS

Wild-type and barcoded A(H1N1)pdm09 viruses that differed by 2 synonymous mutations per gene segment were inoculated into ferrets via intra-nasal and intra-tracheal routes. Naïve recipients were exposed to the exhaled breath of inoculated donors for 8 hours on day 2 post-inoculation. Onward transmission potential of wild-type and barcoded genotypes were monitored by next generation sequencing.

RESULTS

Transmissible airborne particles were respired from the upper but not the lower respiratory epithelial cells of donor ferrets. There was limited mixing of viral populations replicating in the upper and lower respiratory tissues.

CONCLUSIONS

The ferret upper respiratory epithelium was mapped as the anatomic site that generated influenza virus-laden particles mediating onward transmission by air. Our results suggest that vaccines and antivirals should aim to reduce viral loads in the upper respiratory tract for prevention of influenza transmission.

Beyond the Gastrointestinal Tract: The Emerging and Diverse Tissue Tropisms of Astroviruses

Astroviruses are single stranded, positive-sense RNA viruses that have been historically associated with diseases of the gastrointestinal tract of vertebrates, including humans. However, there is now a multitude of evidence demonstrating the capacity of these viruses to cause extraintestinal diseases. The most striking causal relationship is neurological diseases in humans, cattle, pigs, and other mammals, caused by astrovirus infection. Astroviruses have also been associated with disseminated infections, localized disease of the liver or kidneys, and there is increasing evidence suggesting a potential tropism to the respiratory tract. This review will discuss the current understanding of the tissue tropisms for astroviruses and their emerging capacity to cause disease in multiple organ systems.

Insights into the Pathogenesis of Viral Haemorrhagic Fever Based on Virus Tropism and Tissue Lesions of Natural Rift Valley Fever

Rift Valley fever phlebovirus (RVFV) infects humans and a wide range of ungulates and historically has caused devastating epidemics in Africa and the Arabian Peninsula. Lesions of naturally infected cases of Rift Valley fever (RVF) have only been described in detail in sheep with a few reports concerning cattle and humans. The most frequently observed lesion in both ruminants and humans is randomly distributed necrosis, particularly in the liver. Lesions supportive of vascular endothelial injury are also present and include mild hydropericardium, hydrothorax and ascites; marked pulmonary congestion and oedema; lymph node congestion and oedema; and haemorrhages in many tissues. Although a complete understanding of RVF pathogenesis is still lacking, antigen-presenting cells in the skin are likely the early targets of the virus. Following suppression of type I IFN production and necrosis of dermal cells, RVFV spreads systemically, resulting in infection and necrosis of other cells in a variety of organs. Failure of both the innate and adaptive immune responses to control infection is exacerbated by apoptosis of lymphocytes. An excessive pro-inflammatory cytokine and chemokine response leads to microcirculatory dysfunction. Additionally, impairment of the coagulation system results in widespread haemorrhages. Fatal outcomes result from multiorgan failure, oedema in many organs (including the lungs and brain), hypotension, and circulatory shock. Here, we summarize current understanding of RVF cellular tropism as informed by lesions caused by natural infections. We specifically examine how extant knowledge informs current understanding regarding pathogenesis of the haemorrhagic fever form of RVF, identifying opportunities for future research.

Feline Morbillivirus Infection in Domestic Cats: What Have We Learned So Far?

Feline morbillivirus (FeMV) was identified for the first time in stray cats in 2012 in Hong Kong and, since its discovery, it was reported in domestic cats worldwide. Although a potential association between FeMV infection and tubulointerstitial nephritis (TIN) has been suggested, this has not been proven, and the subject remains controversial. TIN is the most frequent histopathological finding in the context of feline chronic kidney disease (CKD), which is one of the major clinical pathologies in feline medicine. FeMV research has mainly focused on defining the epidemiology, the role of FeMV in the development of CKD, and its in vitro tropism, but the pathogenicity of FeMV is still not clear, partly due to its distinctive biological characteristics, as well as to a lack of a cell culture system for its rapid isolation. In this review, we summarize the current knowledge of FeMV infection, including genetic diversity of FeMV strains, epidemiology, pathogenicity, and clinicopathological findings observed in naturally infected cats.

Is the ZIKV Congenital Syndrome and Microcephaly Due to Syndemism with Latent Virus Coinfection?

The emergence of the Zika virus (ZIKV) mirrors its evolutionary nature and, thus, its ability to grow in diversity or complexity (i.e., related to genome, host response, environment changes, tropism, and pathogenicity), leading to it recently joining the circle of closed congenital pathogens. The causal relation of ZIKV to microcephaly is still a much-debated issue. The identification of outbreak foci being in certain endemic urban areas characterized by a high-density population emphasizes that mixed infections might spearhead the recent appearance of a wide range of diseases that were initially attributed to ZIKV. Globally, such coinfections may have both positive and negative effects on viral replication, tropism, host response, and the viral genome. In other words, the possibility of coinfection may necessitate revisiting what is considered to be known regarding the pathogenesis and epidemiology of ZIKV diseases. ZIKV viral coinfections are already being reported with other arboviruses (e.g., chikungunya virus (CHIKV) and dengue virus (DENV)) as well as congenital pathogens (e.g., human immunodeficiency virus (HIV) and cytomegalovirus (HCMV)). However, descriptions of human latent viruses and their impacts on ZIKV disease outcomes in hosts are currently lacking. This review proposes to select some interesting human latent viruses (i.e., herpes simplex virus 2 (HSV-2), Epstein-Barr virus (EBV), human herpesvirus 6 (HHV-6), human parvovirus B19 (B19V), and human papillomavirus (HPV)), whose virological features and co-exposition with ZIKV may provide evidence of the syndemism process, shedding some light on the emergence of the ZIKV-induced global congenital syndrome in South America.

COVID‑19 and SARS‑CoV‑2 host cell entry mediators: Expression profiling of TMRSS4 in health and disease

Severe acute respiratory syndrome (SARS) coronavirus‑2 (SARS‑CoV‑2), the causative viral agent for the ongoing COVID‑19 pandemic, enters its host cells primarily via the binding of the SARS‑CoV‑2 spike (S) proteins to the angiotensin‑converting enzyme 2 (ACE2). A number of other cell entry mediators have also been identified, including neuropilin‑1 (NRP1) and transmembrane protease serine 2 (TMPRSS2). More recently, it has been demonstrated that transmembrane protease serine 4 (TMPRSS4) along with TMPRSS2 activate the SARS‑CoV‑2 S proteins, and enhance the viral infection of human small intestinal enterocytes. To date, a systematic analysis of TMPRSS4 in health and disease is lacking. In the present study, using in silico tools, the gene expression and genetic alteration of TMPRSS4 were analysed across numerous tumours and compared to controls. The observations were also expanded to the level of the central nervous system (CNS). The findings revealed that TMPRSS4 was overexpressed in 11 types of cancer, including lung adenocarcinoma, lung squamous cell carcinoma, cervical squamous cell carcinoma, thyroid carcinoma, ovarian cancer, cancer of the rectum, pancreatic cancer, colon and stomach adenocarcinoma, uterine carcinosarcoma and uterine corpus endometrial carcinoma, whilst it was significantly downregulated in kidney carcinomas, acute myeloid leukaemia, skin cutaneous melanoma and testicular germ cell tumours. Finally, a high TMPRSS4 expression was documented in the olfactory tubercle, paraolfactory gyrus and frontal operculum, all brain regions which are associated with the sense of smell and taste. Collectively, these data suggest that TMPRSS4 may play a role in COVID‑19 symptomatology as another SARS‑CoV‑2 host cell entry mediator responsible for the tropism of this coronavirus both in the periphery and the CNS.

IL-8/CXCR2 mediates tropism of human bone marrow-derived mesenchymal stem cells toward CD133+ /CD44+ Colon cancer stem cells

In cancer treatment, the most attractive feature of mesenchymal stem cells (MSCs) is it's homing to tumor tissues. MSC is an important part of the "colon cancer stem cell niche", but little research has been done on the tropism of human MSCs toward colon cancer stem cells (CCSCs). In this study, we first compared the effects of three tissue-derived MSCs (bone marrow, adipose tissue, and placenta) in vivo on colon tumor xenograft growth. Then, we analyzed the tropism of bone marrow-derived MSCs (BMSCs) toward normal intestinal epithelial cells (NCM460), parental colon cancer cells, CD133- /CD44-, and CD133+ /CD44+ colon cancer cells in vitro. Microarray analysis and in vitro experiments explored the mechanism of mediating the homing of BMSCs toward CCSCs. Compared with the parental and CD133- /CD44- colon cancer cells, CD133+ /CD44+ cells have a stronger ability to recruit BMSCs. In addition, BMSCs were significantly transformed into cancer-associated fibroblasts after being recruited by CCSCs. After coculture of BMSCs and CCSCs, the expression of interleukin (IL)-6, IL-8, IL-32, and CCL20 was significantly increased. Compared with parental strains, CD133- /CD44- cells, and NCM460, BMSC secreted significantly more IL-8 after coculture with CD133+ /CD44+ cells. Low concentration of IL-8 peptide inhibitors (100 ng/ml) and CXC receptor 2 (CXCR2) inhibitors have little effect on the migration of BMSCs, but can effectively weaken CCSC stemness and promote dormant CSCs in the coculture system to re-enter into the cell cycle. The endogenous IL-8 knockout in BMSCs or BMSCs loaded with IL-8 and/or CXCR2 inhibitors will make the therapy of BMSC targeting CCSCs function at its best.

Translational adaptation of human viruses to the tissues they infect

Viruses need to hijack the translational machinery of the host cell for a productive infection to happen. However, given the dynamic landscape of tRNA pools among tissues, it is unclear whether different viruses infecting different tissues have adapted their codon usage toward their tropism. Here, we collect the coding sequences of 502 human-infecting viruses and determine that tropism explains changes in codon usage. Using the tRNA abundances across 23 human tissues from The Cancer Genome Atlas (TCGA), we build an in silico model of translational efficiency that validates the correspondence of the viral codon usage with the translational machinery of their tropism. For instance, we detect that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is specifically adapted to the upper respiratory tract and alveoli. Furthermore, this correspondence is specifically defined in early viral proteins. The observed tissue-specific translational efficiency could be useful for the development of antiviral therapies and vaccines.

SARS-CoV-2 Infection and Disease Modelling Using Stem Cell Technology and Organoids

In this Review, we briefly describe the basic virology and pathogenesis of SARS-CoV-2, highlighting how stem cell technology and organoids can contribute to the understanding of SARS-CoV-2 cell tropisms and the mechanism of disease in the human host, supporting and clarifying findings from clinical studies in infected individuals. We summarize here the results of studies, which used these technologies to investigate SARS-CoV-2 pathogenesis in different organs. Studies with in vitro models of lung epithelia showed that alveolar epithelial type II cells, but not differentiated lung alveolar epithelial type I cells, are key targets of SARS-CoV-2, which triggers cell apoptosis and inflammation, while impairing surfactant production. Experiments with human small intestinal organoids and colonic organoids showed that the gastrointestinal tract is another relevant target for SARS-CoV-2. The virus can infect and replicate in enterocytes and cholangiocytes, inducing cell damage and inflammation. Direct viral damage was also demonstrated in in vitro models of human cardiomyocytes and choroid plexus epithelial cells. At variance, endothelial cells and neurons are poorly susceptible to viral infection, thus supporting the hypothesis that neurological symptoms and vascular damage result from the indirect effects of systemic inflammatory and immunological hyper-responses to SARS-CoV-2 infection.

Persistent Brainstem Dysfunction in Long-COVID: A Hypothesis

Long-COVID is a postviral illness that can affect survivors of COVID-19, regardless of initial disease severity or age. Symptoms of long-COVID include fatigue, dyspnea, gastrointestinal and cardiac problems, cognitive impairments, myalgia, and others. While the possible causes of long-COVID include long-term tissue damage, viral persistence, and chronic inflammation, the review proposes, perhaps for the first time, that persistent brainstem dysfunction may also be involved. This hypothesis can be split into two parts. The first is the brainstem tropism and damage in COVID-19. As the brainstem has a relatively high expression of ACE2 receptor compared with other brain regions, SARS-CoV-2 may exhibit tropism therein. Evidence also exists that neuropilin-1, a co-receptor of SARS-CoV-2, may be expressed in the brainstem. Indeed, autopsy studies have found SARS-CoV-2 RNA and proteins in the brainstem. The brainstem is also highly prone to damage from pathological immune or vascular activation, which has also been observed in autopsy of COVID-19 cases. The second part concerns functions of the brainstem that overlap with symptoms of long-COVID. The brainstem contains numerous distinct nuclei and subparts that regulate the respiratory, cardiovascular, gastrointestinal, and neurological processes, which can be linked to long-COVID. As neurons do not readily regenerate, brainstem dysfunction may be long-lasting and, thus, is long-COVID. Indeed, brainstem dysfunction has been implicated in other similar disorders, such as chronic pain and migraine and myalgic encephalomyelitis or chronic fatigue syndrome.

Intrapatient Evolutionary Dynamics in an Individual Infected with HIV-1 CRF01_AE Who Experienced Periods of Treatment Failure

Although previous studies have analyzed cross-level CRF01_AE viral genomic data in populations, less is known about intrapatient viral evolutionary dynamics during antiretroviral therapy (ART) failure. We longitudinally sampled plasma and peripheral blood mononuclear cells (PBMC) at different time points from one human immunodeficiency virus type 1 infected patient. The evolution of viral quasispecies was inferred from viral phylogenies. Before treatment, no drug-resistant mutations were found in this patient's plasma, and all viruses had C-C chemokine receptor type 5 (CCR5) tropism. Two months after treatment, the majority of the virus population in plasma and PBMC were drug resistant and X4-tropic. By 5 months after treatment, the viral load increased significantly, and viruses reversed tropism from X4 to R5 in plasma and PBMC. During treatment failure, the effective population of the pol DNA reservoir in PBMC remained stable, whereas the env DNA reservoir increased. The effective population of the R5 tropism virus increased more rapidly than that of the X4 tropism virus. The ratio of non-synonymous to synonymous substitutions in the env gene of R5 tropism virus (0.43) was lower than X4 tropism (0.52). However, four env positive selection sites were identified in R5 tropism viruses (HXB2: 364, 398, 399, and 400) but none were identified in X4 tropism viruses. Our data demonstrated the different intrapatient evolutionary dynamics patterns of env and pol genes in an individual who experienced periods of ART failure. Our findings also suggest the importance of the R5 tropism virus in the DNA reservoir during ART failure.

The V617I Substitution in Avian Coronavirus IBV Spike Protein Plays a Crucial Role in Adaptation to Primary Chicken Kidney Cells

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.

Bovine Adenovirus-3 Tropism for Bovine Leukocyte Sub-Populations

A number of characteristics including lack of virulence and the ability to grow to high titers, have made bovine adenovirus-3 (BAdV-3) a vector of choice for further development as a vaccine-delivery vehicle for cattle. Despite the importance of blood leukocytes, including dendritic cells (DC), in the induction of protective immune responses, little is known about the interaction between BAdV-3 and bovine blood leukocytes. Here, we demonstrate that compared to other leukocytes, bovine blood monocytes and neutrophils are significantly transduced by BAdV404a (BAdV-3, expressing enhanced yellow green fluorescent protein [EYFP]) at a MOI of 1-5 without a significant difference in the mean fluorescence of EYFP expression. Moreover, though expression of some BAdV-3-specific proteins was observed, no progeny virions were detected in the transduced monocytes or neutrophils. Interestingly, addition of the "RGD" motif at the C-terminus of BAdV-3 minor capsid protein pIX (BAV888) enhanced the ability of the virus to enter the monocytes without altering the tropism of BAdV-3. The increased uptake of BAV888 by monocytes was associated with a significant increase in viral genome copies and the abundance of EYFP and BAdV-3 19K transcripts compared to BAdV404a-transduced monocytes. Our results suggest that BAdV-3 efficiently transduces monocytes and neutrophils in the absence of viral replication. Moreover, RGD-modified capsid significantly increases vector uptake without affecting the initial interaction with monocytes.

Localization of goose haemorrhagic polyomavirus in naturally infected geese using in situ hybridization

Goose haemorrhagic polyomavirus (GHPV) is the aetiological agent of haemorrhagic nephritis enteritis of geese (HNEG), a fatal disease that impacts geese and has been recorded only in Europe. The present study describes the first clinical cases of HNEG in Taiwan and the phylogenesis of Taiwanese GHPV, and it elucidates the pathogenesis of GHPV infection using in situ hybridization (ISH). The genomes of Taiwanese GHPV were highly similar to the previously reported strains. The diseased geese showed various degrees of vascular damage, especially in the digestive tract. The affected geese in the early stage showed transmural haemorrhagic enteritis in the intestine. In the middle to late stages, the most obvious lesion was hypoxic necrosis of renal tubules around intralobular central veins. Mineralization deposited in the kidney and systemic gout were also found. ISH revealed GHPV DNA in the vascular endothelial cells throughout the body, but not in the parenchymal cells of organs. Accordingly, the pathogenesis of GHPV infection was consistent with viral tropism in the endothelial cells. Specific attack of vascular endothelium by GHPV resulted in endothelial cell necrosis and subsequent increases of blood vessel permeability, as well as secondary circulation disorders, such as oedema, haemorrhage, and ischaemic necrosis in the adjacent parenchyma. RESEARCH HIGHLIGHTS Cell tropism of GHPV is determined by in situ hybridization. The tropism results in vascular dysfunction and subsequent pathobiology. Haemorrhagic nephritis and enteritis of geese described outside Europe for the first time.

The Cell Tropism of Porcine Respiratory Coronavirus for Airway Epithelial Cells Is Determined by the Expression of Porcine Aminopeptidase N

Porcine respiratory coronavirus (PRCoV) infects the epithelial cells in the respiratory tract of pigs, causing a mild respiratory disease. We applied air–liquid interface (ALI) cultures of well-differentiated porcine airway cells to mimic the respiratory tract epithelium in vitro and use it for analyzing the infection by PRCoV. As reported for most coronaviruses, virus entry and virus release occurred mainly via the apical membrane domain. A novel finding was that PRCoV preferentially targets non-ciliated and among them the non-mucus-producing cells. Aminopeptidase N (APN), the cellular receptor for PRCoV was also more abundantly expressed on this type of cell suggesting that APN is a determinant of the cell tropism. Interestingly, differentiation-dependent differences were found both in the expression of pAPN and the susceptibility to PRCoV infection. Cells in an early differentiation stage express higher levels of pAPN and are more susceptible to infection by PRCoV than are well-differentiated cells. A difference in the susceptibility to infection was also detected when tracheal and bronchial cells were compared. The increased susceptibility to infection of bronchial epithelial cells was, however, not due to an increased abundance of APN on the cell surface. Our data reveal a complex pattern of infection in porcine differentiated airway epithelial cells that could not be elucidated with immortalized cell lines. The results are expected to have relevance also for the analysis of other respiratory viruses.

Treatment with Exogenous Trypsin Expands In Vitro Cellular Tropism of the Avian Coronavirus Infectious Bronchitis Virus

The Gammacoronavirus infectious bronchitis virus (IBV) causes a highly contagious and economically important respiratory disease in poultry. In the laboratory, most IBV strains are restricted to replication in ex vivo organ cultures or in ovo and do not replicate in cell culture, making the study of their basic virology difficult. Entry of IBV into cells is facilitated by the large glycoprotein on the surface of the virion, the spike (S) protein, comprised of S1 and S2 subunits. Previous research showed that the S2' cleavage site is responsible for the extended tropism of the IBV Beaudette strain. This study aims to investigate whether protease treatment can extend the tropism of other IBV strains. Here we demonstrate that the addition of exogenous trypsin during IBV propagation in cell culture results in significantly increased viral titres. Using a panel of IBV strains, exhibiting varied tropisms, the effects of spike cleavage on entry and replication were assessed by serial passage cell culture in the presence of trypsin. Replication could be maintained over serial passages, indicating that the addition of exogenous protease is sufficient to overcome the barrier to infection. Mutations were identified in both S1 and S2 subunits following serial passage in cell culture. This work provides a proof of concept that exogenous proteases can remove the barrier to IBV replication in otherwise non-permissive cells, providing a platform for further study of elusive field strains and enabling sustainable vaccine production in vitro.