Human norovirus replicates in macrophages migrating to intestinal tissues and changes their transcriptional profile
Human noroviruses (HuNoVs) are a major cause of diarrheal disease, yet critical aspects of their biology, including cellular tropism, remain unclear. While research traditionally focused on the intestinal epithelium, the hypothesis that HuNoV infects macrophages has been recurrently discussed and is investigated here by a zebrafish larval model. Our study reveals that HuNoV capsid proteins and double-stranded RNA colocalize within intestinal macrophages of infected zebrafish larvae, while the negative-strand RNA intermediate was detected within FACS-sorted macrophages. Flow cytometry confirms viral replication within these macrophages, constituting ~9% of HuNoV?s host cells. Single-cell RNA-sequencing reaffirms their role in viral replication, as all three open reading frames were mapped to individual macrophages. Yet, macrophages were not required for productive infection given the limited changes in viral loads upon their absence. Identifying macrophages as host cells prompts a reevaluation of their role in HuNoV pathogenesis, offering new directions for understanding and controlling this infection. Overall design: Intestines of uninfected and HuNoV-infected zebrafish larvae were dissected and subjected to the preparation of a single-cell suspension that was analyzed using scRNAseq. Subsequently, an additional sample was analyzed on FACS-sorted macrophages of HuNoV-infected zebrafish larvae.