Objective  To construct the prokaryotic expression vector of mouse CD25 extracellular domain and to express it in E coli.   Methods  Total RNA was isolated from splenocytes of Balb/c mice. The CD25 extracellular domain gene was amplified by RT-PCR and cloned into the PET-32a vector. A positive recombinant

PET-32a-CD25e

was identified by enzyme cleaving and sequencing before its expression in E. coli

and transferred into E. coli BL21 (DE3) plysS for its expression. After purification with Ni

+

resin and renaturation in vitro

a relative molecular mass (Mr) of the interesting protein was detected by SDS-PAGE and Western blotting. Effect of the puri

fied interesting protein on the proliferation of splenocytes from T cell vaccine-immunized syngeneic mice was detected by MTT assay.   Results  The cloned CD25 extracellular domain gene was identified to be functional by sequencing and expression. The purified interesting protein could significantly induce the proliferation and IL-4 secretion of splenocytes from T cell vaccine-immunized mice in vitro.   Conclusion  Mouse CD25 extracellular domain gene can be successfully expressed in prokaryotic cells with biological activity

which lays a foundation for further relative studies.