A DNA sequence encoding the extracellular domain (Met 1-Pro 1107) of human ITGAX (P20702) was fused with a flag tag at the C-terminus, constructed the plasmid 1; A DNA sequence encoding the extracellular domain (Met 1-Asn 700) of human ITGB2 (P05107) was fused with a polyhistidine tag at the C-terminus, constructed the plasmid 2. The two plasmids were co-expressed and the heterodimer was purified.