NF-kappaB2 is required for the establishment of central tolerance through an Aire-dependent pathway

A role for the IkappaB family member Bcl-3 in the control of central immunologic tolerance

Bcl-3 is a member of the family of IkappaB inhibitors. Unlike the classical, cytoplasmic IkappaBs, Bcl-3 does not inhibit RelA- or c-Rel-containing NF-kappaB transcription factor dimers. Instead, Bcl-3 can enter the nucleus and modulate NF-kappaB activity, although the underlying mechanism and physiologic function remain largely unknown. Here we identified Bcl-3 as a regulator of immunologic tolerance to self. In parallel with NF-kappaB2, Bcl-3 functions within stroma to generate medullary thymic epithelial cells, which are essential for negative selection of autoreactive T cells. Loss of both NF-kappaB2 and Bcl-3, but not either one alone, led to a profound breakdown in central tolerance resulting in rapid and fatal multiorgan inflammation. These data reveal extensive utilization of the NF-kappaB system to promote central tolerance in the thymus, in apparent contrast with the well-known roles of NF-kappaB to promote inflammation and autoimmunity in the periphery.

What's new in the Aire?

Unraveling the mechanisms underlying autoimmune disease remains a difficult challenge. Recent lessons learned from the study of AIRE (autoimmune regulator), the gene responsible for the rare monogenic human syndrome APS-1, highlight the power of genetics to reveal disease pathogenesis. With the discovery of AIRE, central tolerance has re-emerged as a crucial check against autoimmunity. Aire-mediated regulation of diverse self-antigens in the thymus serves as a paradigm for the importance of promiscuous gene expression in the prevention of autoimmune disease. Recent characterization of Aire-targeted antigens continues to bear this out. Here, we review the current progress surrounding the role of Aire in central tolerance from a molecular, genetic and developmental basis.

Lessons on immune tolerance from the monogenic disease APS1

Autoimmunity is a complex disease process that results from a breakdown in the ability of the immune system to discriminate self from non-self. One approach to unraveling how autoimmunity occurs is to study monogenic diseases, for which a single gene defect is responsible. Recent work on the monogenic autoimmune disease 'autoimmune polyglandular syndrome type 1' (APS1) and on the causal gene of this disorder--autoimmune regulator (AIRE)--is providing new lessons on how immune tolerance is maintained.

NF-kappa B as a therapeutic target in autoimmune disease

NF-kappaB transmits signals from the cell surface to the nucleus. Signaling through cell surface receptors to activate NF-kappaB and mitogen-activated protein kinases through adaptor molecules is of critical importance to survival and activation of all cells in the body, including those regulating innate and adaptive immunity. As such, NF-kappaB is a key signaling component in autoimmunity and an attractive target for autoimmune disease therapy. However, given its global importance, targeting NF-kappaB tends to be immunosuppressive. In this review, the authors discuss the roles played by NF-kappaB in autoimmunity, drugs which target it, and complexities which need to be addressed to improve the use of NF-kappaB as a target. Finally, the authors highlight some novel approaches that are likely to be important in the next generation of NF-kappaB therapies.

The unconventional role of LT alpha beta in T cell differentiation

Lymphotoxin (LT)alphabeta, a member of the tumor necrosis factor cytokine superfamily, and its receptor, the LTbeta receptor (LTbetaR), have a well defined role in secondary lymphoid organogenesis but an unexpected function in T cell differentiation. Although earlier studies indicated that conventional T cell subsets were normal in mice deficient in the LTbetaR pathway, accumulating evidence indicates that the LTalphabeta-LTbetaR pathway has a pivotal role in the ontogeny of unconventional T cells, including gammadelta T cells and invariant natural killer T cells. The LTbetaR pathway seems to operate at distinct levels during thymic development. Double positive thymocytes regulate the differentiation of early thymocyte progenitors and gammadelta T cells through a mechanism dependent on LTbetaR. In addition, LTbetaR signaling in thymic stroma was proposed to affect central tolerance to peripherally restricted antigens. These findings highlight the complex cellular crosstalk between lymphoid and stromal compartments during thymic differentiation.