Paneth cells, which reside in crypts, are the target of GVHD, defend against pathogens and regulate immune responses through the production of antimicrobial peptides (AMPs), including defensins and C-type lectin regenerating islet derived protein 3 (REG3; REG3α in humans and REG3γ in mice) [61, 64, 65]. This evidence concerns the gene REG3G and graft versus host disease.