BCR and mantle cell lymphoma: It is worth mentioning in this respect that MCL cells have a constitutive activation of the BCR signal transduction proteins Syk and PKCβII [35,36] as well as high expression of the phosphorylated forms of these and other BCR-associated kinases.[37] These findings may at least partly explain why MCL cell lines apparently respond with enhanced proliferation to TLR1/2 or TLR5 triggering without the requirement of additional co-stimuli.