Ac9-25 acetate is an annexin AI peptide and activates the neutrophil reduced nicotinamide adenine dinucleotide phosphate oxidase through FPR but not through FPRL1.

At a concentration of 20 μM, the N-terminal annexin I peptides Ac9-25 acetate markedly interfere with the transendothelial passage of neutrophils. Peptides derived from the N-terminal domains of other annexins do not elicit an inhibitory effect. Titration experiments show that a 50% inhibition of neutrophil transmigration is observed at ～5 μM annexin I peptide with Ac9-25 acetate[1].