Tissue TG2 is expressed in MCL. (A) Immunocytochemistry analyses showed that the MCL cell lines SP-53 and Jeko-1 were positive for TG2 expression. Confocal microscopic images showed the localization of TG2 in the cytoplasm in MCL cells. Arrows in each panel indicate representative signals. (B) Xenograft tumor and spleen sections generated from sorted CD45⁺CD19⁻ MCL-ICs were immunostained for TG2 protein expression. Representative sections with positive immunostaining for the anti–human TG2 Ab and the anti–human IgG Ab as a control are shown. The xenograft tumors and spleens expressed high levels of human TG2 (arrows). At least 5 sections from each xenograft tumor were analyzed. (C) Immunoblot analyses of TG2 expression were performed using cell lysate proteins of 4 different MCL cell lines, SP-53, Jeko-1, Mino, and REC-1. The breast cancer cell line MDA-MB-231 was used as a positive control and normal B cells were used as negative controls. β-actin was also used as a control. TG2 was expressed in MCL cells. (D) TG2 enzymatic activity was measured using TG2-CovTest TG2-specific colorimetric assay kit (Novus Biologicals) using extracts from SP-53, Jeko-1, Mino, and REC-1 cells. Recombinant human TG2 was used as a positive control, and normal B cells were used as negative controls. Comparable levels of enzymatic activities were noted between the different MCL cell lines.