HLA class II histocompatibility antigen gamma chain isoform b, also known as CD74, is a transmembrane protein which, on antigen presenting cells, is the invariant chain that chaperones MHC class II dimers from the endoplasmic reticulum to the cell surface. CD74 is expressed by cells of both T lymphocyte and B lymphocyte lineages. It is upregulated in several cancers and is also expressed by nonimmune cells during inflammation. Recombinant human CD74 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.