N-Ethyl-N-nitrosourea mutagenesis in the mouse provides strong genetic and in vivo evidence for the role of the Caspase Recruitment Domain (CARD) of CARD-MAGUK1 in T regulatory cell development

CARD11 signaling in regulatory T cell development and function

Regulatory T cells (Tregs) are a critical subset of CD4 T cells that modulate the immune response to prevent autoimmunity and chronic inflammation. CARD11, a signaling hub and scaffold protein that links antigen receptor engagement to activation of NF-κB and other downstream signaling pathways, is essential for the development and function of thymic Tregs. Mouse models with deficiencies in CARD11 and CARD11-associated signaling components generally have Treg defects, but some mouse models develop overt autoimmunity and inflammatory disease whereas others do not. Inhibition of CARD11 signaling in Tregs within the tumor microenvironment can potentially promote anti-tumor immunity. In this review, we summarize evidence for the involvement of CARD11 signaling in Treg development and function and discuss key unanswered questions and future research opportunities.

Malt1 protease inactivation efficiently dampens immune responses but causes spontaneous autoimmunity

The protease activity of the paracaspase Malt1 has recently gained interest as a drug target for immunomodulation and the treatment of diffuse large B-cell lymphomas. To address the consequences of Malt1 protease inactivation on the immune response in vivo, we generated knock-in mice expressing a catalytically inactive C472A mutant of Malt1 that conserves its scaffold function. Like Malt1-deficient mice, knock-in mice had strong defects in the activation of lymphocytes, NK and dendritic cells, and the development of B1 and marginal zone B cells and were completely protected against the induction of autoimmune encephalomyelitis. Malt1 inactivation also protected the mice from experimental induction of colitis. However, Malt1 knock-in mice but not Malt1-deficient mice spontaneously developed signs of autoimmune gastritis that correlated with an absence of Treg cells, an accumulation of T cells with an activated phenotype and high serum levels of IgE and IgG1. Thus, removal of the enzymatic activity of Malt1 efficiently dampens the immune response, but favors autoimmunity through impaired Treg development, which could be relevant for therapeutic Malt1-targeting strategies.