If the MCL precursor cell indeed represented an activated pre-GC B cell, one may speculate that, based on the in vivo observation that c-REL is required for B-cell activation prior to the GC reaction, whereas RELA is dispensable at this step [32] (Figure 2), c-REL may represent the critical NF-κB subunit in MCL pathogenesis (Figure 3). This evidence concerns the gene NFKB1 and mantle cell lymphoma.