A DNA sequence encoding the rat IL23A (NP_569094.1) (Met1-Ala196) was fused with a polyhistidine tag at the C-terminus, constructed the plasmid 1; A DNA sequence encoding the rat IL12B (EDM04146.1) (Met1-Ser335) was expressed with a polyhistidine tag at the C-terminus, constructed the plasmid 2. The two plasmids were co-expressed and the rat IL23A & the rat IL12B heterodimer was purified.