MALT1 expression and activity in MCL. (A) Immunohistochemical MALT1 staining of a MALT1-positive MCL case (left; original magnification ×200) and a MALT1-negative MCL case (right; original magnification ×100). Images were captured using a Leitz DMRB microscope (Leica Microsystems, Wetzlar, Germany) equipped with Fluotar objective lenses (10×/0.30 numeric aperture, 20×/0.50 numeric aperture) and a KY-F75U digital camera (Victor, Yokohama, Japan) and were processed with the Diskus Program 4.20 (Hilgers Technical, Königswinter, Germany) that converts and exports images in .jpg file format. (B) MALT1 expression in MCLs determined by immunohistochemistry. (C) Western blot analysis of MALT1, full-length and cleaved forms of CYLD, and MYC. MALT1 was highly expressed in CD20⁺ cells isolated from either PBMCs (patient samples 1 and 2) or lymph nodes (patient samples 3-5) of 5 primary MCL patient samples. Cleaved CYLD indicating MALT1 proteolytic activity was detectable in 4 of 5 patient samples. MYC expression was higher in these 4 samples with activated MALT1. The MCL cell line Z-138 was used as a positive control for MALT1 expression and as a negative control for CYLD cleavage. *Nonspecific band, which was not observed in any MALT1-activated MCL cell lines (Figure 1E). (D) Western blot analysis of MALT1 expression in MCL cell lines. MALT1 protein expression was detectable in all MCL cell lines. (E) Western blot analysis of different MALT1 targets. Cleaved forms of CYLD, RelB, A20, and BCL10 were detectable in Mino, Jeko-1, Rec-1, SP49, and SP53 cells. *Nonspecific band.