Infection by (re-)emerging RNA arboviruses including Chikungunya virus (CHIKV) and Mayaro virus primarily cause acute febrile disease and transient polyarthralgia. However, in a significant subset of infected individuals, debilitating arthralgia persists for weeks over months up to years. The underlying immunopathogenesis of chronification of arthralgia upon primary RNA-viral infection remains unclear. Here, we analysed cell-intrinsic responses to ex vivo arthritogenic alphaviral infection of primary human synovial fibroblasts isolated from knee joints, one the most affected joint types during acute and chronic CHIKV disease. Synovial fibroblasts were susceptible and permissive to alphaviral infection. Base-line and exogenously added type I interferon (IFN) partially and potently restricted infection, respectively. RNA-seq revealed a CHIKV infection-induced transcriptional profile that comprised upregulation of expression of several hundred IFN-stimulated and arthralgia-mediating genes. Single-cell virus-inclusive RNA-seq uncovered a fine-tuned switch from induction to repression of cell-intrinsic immune responses depending on the abundance of viral RNA in an individual cell. Specifically, responses were most pronounced in cells displaying low-to-intermediate amounts of viral RNA and absence of virus-encoded, fluorescent reporter protein expression, arguing for efficient counteraction of innate immunity in cells expressing viral antagonists at sufficient quantities. In summary, cell-intrinsic sensing of viral RNA that potentially persists or replicates at low levels in synovial fibroblasts and other target cell types in vivo may contribute to the chronic arthralgia induced by alphaviral infections. Our findings might advance our understanding of the immunopathophysiology of long-term pathogenesis of RNA-viral infections.

Infection by (re-)emerging RNA arboviruses including Chikungunya virus (CHIKV) and Mayaro virus primarily cause acute febrile disease and transient polyarthralgia. However, in a significant subset of infected individuals, debilitating arthralgia persists for weeks over months up to years. The underlying immunopathogenesis of chronification of arthralgia upon primary RNA-viral infection remains unclear. Here, we analysed cell-intrinsic responses to ex vivo arthritogenic alphaviral infection of primary human synovial fibroblasts isolated from knee joints, one the most affected joint types during acute and chronic CHIKV disease. Synovial fibroblasts were susceptible and permissive to alphaviral infection. Base-line and exogenously added type I interferon (IFN) partially and potently restricted infection, respectively. RNA-seq revealed a CHIKV infection-induced transcriptional profile that comprised upregulation of expression of several hundred IFN-stimulated and arthralgia-mediating genes. Single-cell virus-inclusive RNA-seq uncovered a fine-tuned switch from induction to repression of cell-intrinsic immune responses depending on the abundance of viral RNA in an individual cell. Specifically, responses were most pronounced in cells displaying low-to-intermediate amounts of viral RNA and absence of virus-encoded, fluorescent reporter protein expression, arguing for efficient counteraction of innate immunity in cells expressing viral antagonists at sufficient quantities. In summary, cell-intrinsic sensing of viral RNA that potentially persists or replicates at low levels in synovial fibroblasts and other target cell types in vivo may contribute to the chronic arthralgia induced by alphaviral infections. Our findings might advance our understanding of the immunopathophysiology of long-term pathogenesis of RNA-viral infections.

Single-cell RNA-Seq of airway samples of COVID-19 patients and healthy controls
This dataset comprises single-cell RNA-Seq data of nasopharyngeal, protected specimen brush, and bronchial lavage samples of 19 COVID-19 patients (eight moderate and eleven critical according to the WHO classification) and five healthy controls, for a total of 36 samples.
An in-depth description is presented in the manuscript "Cross-talk between the airway epithelium and activated immune cells defines severity in COVID-19" (https://www.medrxiv.org/content/10.1101/2020.04.29.20084327v1).
The data is uploaded as two .rds files of Seurat objects that can be imported into R. The _main file contains all samples from the nasopharynx, while the _loc file contains data from nasopharyngeal, protected specimen brush, and bronchial lavage samples of two patients.
A quantification of viral RNA reads (as CPM, in total over cells and background) is provided as .xlsx file. Please note that these values may differ from viral load estimates obtained from diagnostic procedures and may be less accurate.Raw count values (cellranger output) are provided in the file count_matrices_NBT.tar.

This dataset comprises single-cell RNA-Seq data of nasopharyngeal samples of 32 COVID-19 patients and 16 healthy controls, for a total of 48 samples. 25 COVID-19 patients and 10 controls were diagnosed with hypertension and treated with either ACE inhibitors (ACEi) or angiotensin receptor blockers(ARB) (SARS-CoV-2-positive: 10 ACEi and 15 ARB; SARS-CoV-2-negative: 6 ACEi and 4 ARB).
An in-depth description is presented in the manuscript "Delayed viral clearance and exacerbated airway hyperinflammation in hypertensive COVID-19 patients" (https://www.medrxiv.org/content/10.1101/2020.09.22.20199471v1).