The EPX gene encodes for eosinophil peroxidase, a protein primarily expressed in eosinophils and to a lesser extent, in other cell types such as macrophages and kidney epithelial cells. The encoded preproprotein is post-translationally processed into covalently attached heavy and light chains that form the mature enzyme. This enzyme, functioning as a powerful oxidant, plays a critical role in the immune system by generating toxic molecules from hydrogen peroxide and halides to kill parasitic worms and protozoa ^[1]. It is released from eosinophils at sites of infection or allergen stimulation, acting as both an effector molecule for cytotoxicity and a biomarker for eosinophilic inflammation ^[2]. Mutations in this gene can lead to eosinophil peroxidase deficiency.

Epx-iCre mice were generated using gene editing technology to integrate an iCre-FRT-Neo-FRT-IRES expression cassette into the upstream of the ATG start codon of the mouse endogenous Epx gene. Under the control of the Epx gene's regulatory elements, the iCre recombinase (a codon-optimized Cre recombinase) is expressed. The FRT-Neo-FRT element is used to screen positive clones during the construction process, and the mice delivered to the customer have completed self-deletion of the Neo element. When Epx-iCre mice are crossed with mice containing loxP sites, Cre recombinase-mediated sequence recombination between loxP sites is expected to occur in Epx-positive cells of the offspring.