Gp(2′-5′)Ap sodium is a linear dinucleotide analog after hydrolysis of cyclic guanosine monophosphate- adenosine monophosphate (2’3’-cGAMP) by phosphodiesterases. Due to its linear conformation, 2’5’GpAp is intended to serve as a negative control for 2’3’-cGAMP in type I IFN induction assays.