Secondary, non-inflammatory osteoarthritis (OA) is a common disorder in dogs. Its silent onset prevents early diagnosis and delays treatment. Synovial fluid biomarkers can detect OA at an early stage, before the presence of radiographic signs. In addition, these local biomarkers can aid prognosis of the disease, monitor the response to treatment and can be used to assess the degree of OA. Currently three groups of canine synovial fluid biomarkers have been the focus of research: proinflammatory mediators, enzymes and their inhibitors, and extracellular cartilage degeneration products. These have been investigated in the elbow, hip and stifle joints of both normal dogs and dogs with naturally occurring and experimentally induced OA. None of these biomarkers are currently used in practice for the detection of canine OA at an early stage. A positive relationship between canine synovial fluid biomarkers and OA has been demonstrated, yet no molecular diagnostic test has been developed so far.

Feline infectious peritonitis (FIP) is a fatal disease caused by feline infectious peritonitis virus (FIPV). At present, neither a licensed treatment nor an accurate ante-mortem diagnosis are available. In the present study, three available tests were evaluated for their diagnostic power on effusion samples. High feline coronavirus antibody titers, measured with an immunoperoxidase monolayer assay (IPMA), were correlated with FIP but its low specificity precluded a reliable diagnosis. The in-house 5’ reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) provided a much better specificity and high sensitivity. Given the low sensitivity of immunofluorescence staining (IF) of effusive cells, the RT-qPCR alone or in combination with IPMA represents a good alternative for IF. In the majority of the effusion samples from FIP positive animals, Sanger sequencing of the open reading frame encoding the spike protein (ORF S) revealed not only mutations that were previously associated with FIP (M1058L, S1060A, I1106T and D1108Y/E/G) but also two new, closely related mutations (T1112S/N).

To face the continuous emergence of SARS-CoV-2 variants, broadly protective therapeutic antibodies are highly needed. We here focused on the fusion peptide (FP) region of the viral spike antigen since it is highly conserved among alpha- and betacoronaviruses. First, we found that coronavirus cross-reactive antibodies are commonly formed during infection, being omnipresent in sera from COVID-19 patients, in ~50% of pre-pandemic human sera (rich in antibodies against endemic human coronaviruses), and even in feline coronavirus-infected cats. Pepscan analyses demonstrated that a confined N-terminal region of the FP is strongly immunogenic across diverse coronaviruses. Peptide-purified human antibodies targeting this conserved FP epitope exhibited broad binding of alpha- and betacoronaviruses, besides weak and transient SARS-CoV-2 neutralizing activity. Being frequently elicited by coronavirus infection, these FP-binding antibodies might potentially exhibit Fc-mediated effector functions and influence the kinetics or severity of coronavirus infection and disease.

No abstract

Feline coronavirus (FCoV) has been identified as the aetiological agent of feline infectious peritonitis (FIP), a highly fatal systemic disease in cats. FCoV open reading frame 3 (ORF3) encodes accessory proteins 3a, 3b and 3 c. The FCoV 3b accessory protein consists of 72 amino acid residues and localizes to nucleoli and mitochondria. The present work focused on peptide domains within FCoV 3b that drive its intracellular trafficking. Transfection of different cell types with FCoV 3b fused to enhanced green fluorescent protein (EGFP) or 3×FLAG confirmed localization of FCoV 3b in the mitochondria and nucleoli. Using serial truncated mutants, we showed that nucleolar accumulation is controlled by a joint nucleolar and nuclear localization signal (NoLS/NLS) in which the identified overlapping pat4 motifs (residues 53–57) play a critical role. Mutational analysis also revealed that mitochondrial translocation is mediated by N-terminal residues 10–35, in which a Tom20 recognition motif (residues 13–17) and two other overlapping hexamers (residues 24–30) associated with mitochondrial targeting were identified. In addition, a second Tom20 recognition motif was identified further downstream (residues 61–65), although the mitochondrial translocation evoked by these residues seemed less efficient as a diffuse cytoplasmic distribution was also observed. Assessing the spatiotemporal distribution of FCoV 3b did not provide convincing evidence of dynamic shuttling behaviour between the nucleoli and the mitochondria.