The CD74 gene encodes the invariant chain (Ii), which is critical in the formation and transport of MHC class II peptide complexes for the generation of CD4+ T-cell responses and is upregulated in the epithelium of IBD patients56–58 where in response to inflammation, it contributes to tissue repair and mucosal healing by acting as the receptor for macrophage migration inhibitory factor (MIF)58–61Fig. 6d depicts elevated Cd74 mRNA expression in the proximal and distal segments of CD_L3 recipients. Here, CD4 is linked to inflammatory bowel disease.