HLA class II histocompatibility antigen gamma chain also known as HLA-DR antigens-associated invariant chain or CD74 (Cluster of Differentiation 74), is a protein that in humans is encoded by the CD74 gene. The invariant chain (Abbreviated Ii) is a polypeptide which plays a critical role in antigen presentation. It is involved in the formation and transport of MHC class II peptide complexes for the generation of CD4+ T cell responses. The cell surface form of the invariant chain is known as CD74. CD74 is a cell surface receptor for the cytokine macrophage migration inhibitory factor (MIF).

Gene targeting strategy for B-hCD74 mice. The exons 2-9 of mouse Cd74 gene that encode extracellular domain, transmembrane domain and 3’UTR region is replaced by human counterparts in B-hCD74 mice. The genomic region of mouse Cd74 gene that encodes cytoplasmic portion is retained. The promoter and 5’UTR region of the mouse gene are also retained. The chimeric CD74 expression is driven by endogenous mouse Cd74 promoter, while mouse Cd74 gene transcription and translation will be disrupted. 

Strain specific analysis of CD74 mRNA expression in wild-type C57BL/6N mice and B-hCD74 mice by RT-PCR. Spleen RNA were isolated from wild-type C57BL/6N mice (+/+) and homozygous B-hCD74 mice (H/H). Mouse Cd74 mRNA was detectable in wild-type C57BL/6N mice. Human CD74 mRNA was detectable only in homozygous B-hCD74 mice but not in wild-type mice. 

Strain specific CD74 expression analysis in B-hCD74 mice by flow cytometry. Splenocytes were collected from wild-type C57BL/6N mice (+/+) and B-hCD74 mice (H/H) , and analyzed by flow cytometry with anti-CD74 antibody (Biolegend, 151003; Biolegend, 326811). mCD74 was detectable in wild-type mice and homozygous B-hCD74 mice, as the antibody is cross-recognized between human and mouse CD74. hCD74 was detectable in homozygous B-hCD74 mice.

Strain specific CD74 expression analysis in B-hCD74 mice by flow cytometry. Splenocytes were collected from wild-type C57BL/6N mice (+/+) and B-hCD74 mice (H/H) , and analyzed by flow cytometry with anti-CD74 antibody (Biolegend, 151003; Biolegend, 326811). mCD74 was detectable in wild-type mice and homozygous B-hCD74 mice, as the antibody is cross-recognized between human and mouse CD74. hCD74 was detectable in homozygous B-hCD74 mice.

Frequency of leukocyte subpopulations in spleen by flow cytometry. Splenocytes and blood were isolated from wild-type C57BL/6N mice (Female, n=3, 7-week-old) and homozygous B-hCD74 mice (Female, n=3, 7-week-old). A. Flow cytometry analysis of the splenocytes and blood were performed to assess the frequency of leukocyte subpopulations. B. Frequency of T cell of splenocytes and blood subpopulations. Percentages of T cells, B cells, NK cells, dendritic cells, monocytes, macrophages, CD4+ T cells, CD8+ T cells and Tregs in B-hCD74 mice  were similar to those in Female, n=3, 7-week-old mice.