Synthetic double-stranded RNA in antiviral immunity and vaccine adjuvant: insights into poly(I:C) and poly(A:U).

Synthetic double-stranded RNA (dsRNA) analogues function as viral mimetics that activate innate immune signaling pathways critical for antiviral defense and the induction of adaptive immunity. Among dsRNA analogues, polyinosinic:polycytidylic acid [poly(I:C)] and polyadenylic:polyuridylic acid [poly(A:U)] have been extensively studied for their immunostimulatory properties and potential as vaccine adjuvants. This review examines how host pattern-recognition receptors sense synthetic dsRNA and explains the rationale for using poly(I:C) and poly(A:U) as representative dsRNA analogues with distinct structural and signaling properties. We compare their antiviral and adjuvant activities, emphasizing differences and commonalities in receptor engagement, downstream signaling, immunogenicity, and safety. Finally, we address emerging applications, translational challenges, and future directions for the rational design and clinical development of dsRNA-based immunomodulators in antiviral immunity and vaccine strategies.