c[U(2′,5′)pA(3′,5′)p]

c[U(2′,5′)pA(3′,5′)p] is a hybrid purine-pyrimidine cyclic dinucleotide that was identified as a natural nucleotide second messenger in the oyster species Crassostrea gigas (C. gigas, Pacific oyster) and Crassostrea virginica (C. virginica, Eastern oyster). In C. virginica, c[U(2′,5′)pA(3′,5′)p] induced a gene expression pattern strongly associated with innate immunity, including upregulated expression of genes encoding transcription factors (NF-kB, IRFs, and STATs), immune receptors (NLRs, RLRs, cGLRs, and STING), and proteins with homology to human interleukins and inhibitor of apoptosis (IAP) factors.