MKI67 and hepatocellular carcinoma: Consistent with the limited tumor burden, HCC tumors from IL-21R-deficient mice were also characterized by lower expression of proliferation markers, including cyclin D1 (Ccnd1), antigen identified by monoclonal antibody Ki67 (Mki67) and cyclin dependent kinase 4 (Cdk4) (Fig. S3E), implying reduced proliferative capacity of tumors in the absence of IL-21R, which was further confirmed by IHC staining for Ki67 (Fig. S3F).