Lymphocyte activation plays a critical role in immune responses and a defect results in severe immune deficiencies/lymphoma. The paracaspase MALT1 is of special interest, although the mechanism by which MALT1 triggers NF-kB activation is still largely unclear. The aim of this project is to study, by using newly generated mouse models, (1) MALT1 inactive and (2) MALT1 resistant A20, and also analyze the effect of MALT1 peptide inhibitors.