PI3 is an elastase-specific protease inhibitor, which contains a WAP-type four-disulfide core (WFDC) domain, and is thus a member of the WFDC domain family. Most WFDC gene members are localized to chromosome 20q12-q13 in two clusters: centromeric and telomeric. PI3 belongs to the centromeric cluster. Recombinant human PI3 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.