Huang, P.; Wang, H.; Xu, S.; Li, M.; Guo, M.; Wang, H.; Gou, X.; Wang, C.; He, Y.; Pan, W.

Abstract Background: The Chikungunya virus (CHIKV), a re-emerging mosquito-borne alphavirus, is responsible for acute febrile illness and severe polyarthralgia. Although both innate and adaptive immune responses influence the disease outcomes, the detailed cellular immunopathogenesis of CHIKV in peripheral blood is not yet fully elucidated. Methods: We conducted single-cell RNA sequencing (scRNA-seq) on peripheral blood mononuclear cells (PBMCs) obtained from patients acutely infected with CHIKV and from healthy control subjects. Cellular interactions were inferred, and the transcriptomic results were orthogonally validated through quantitative real-time PCR (qPCR) and Enzyme-Linked Immunosorbent Assay (ELISA) to assess systemic interferon-stimulated responses. Furthermore, a comparative analysis was performed using publicly available single-cell data from Dengue virus (DENV) infections. Results: CHIKV infection significantly altered the immune system, increasing monocytes and dendritic cells while reducing T and B lymphocytes. Monocytes and NK cells showed strong activation of interferon-stimulated genes (ISGs). Monocytes were identified as key in driving inflammatory and immune responses. In adaptive immunity, CHIKV led B cells to become plasmablasts with antiviral immunoglobulins and caused T cells and NK-like T cells to show signs of cytotoxicity and exhaustion. Validation showed increased levels of IFN-{gamma}, IFN-{beta}1, MX1, and ISG15. CHIKV triggered a more intense, monocyte-driven interferon response than DENV. Conclusions: Acute CHIKV infection induces a systemic interferon response predominantly centered on monocytes, accompanied by significant alterations in adaptive immunity. Circulating ISG products, including MX1 and ISG15, reflect the transcriptomic activation and may serve as potential biomarkers for assessing the early intensity of innate antiviral responses.