Mechanisms of Immunodeficiency Due To NFkappaB Signaling Defects

Abstract

Ectodermal dysplasia with immunodeficiency (ED-ID) is a rare primary immunodeficiency syndrome characterized by defects in ectodermal tissues (skin, hair and sweat glands), recurrent infections, impaired response to Toll-like receptor ligands, hypogammaglobulinemia and deficient antibody production. It is caused by defective \(NF\kappa B\) signaling. The most common form of ED-ID is X-linked. It is caused by hypomorphic mutations in the \(NF\kappa B\) essential modifier gene NEMO, which is an important regulatory component in the \(NF\kappa B\) signaling pathway. We report the first case of ED-ID caused by insufficient expression of a NEMO protein of normal sequence, due to a mutation in the 5’ untranslated region of the NEMO gene. Autosomal dominant ED-ID, a rare form of ED-ID, has been reported to be caused by a heterozygous S32I mutation in the \(I \kappa B \alpha\). This mutation prevents IκBα phosphorylation and inhibits its degradation. The mutant sequesters \(NF\kappa B\) in the cytoplasm and acts as a dominant negative. We report the first ED-ID patient with a heterozygous mutation (W11X) that causes N-terminal truncation of \(I \kappa B \alpha\) and results in functional haploinsufficiency. We have constructed a knock-in mouse model of ED-ID caused by a heterozygous S32I mutation in \(I \kappa B \alpha\). The mutant mice had ED, increased mortality, complete lack of lymph nodes and Peyer’s patches, and disorganized spleens that lacked follicles, marginal zone B cells and follicular dendritic cells. T cell proliferation and cytokine production was normal in vitro, but in vivo contact hypersensitivity was severely impaired, B cell function in vitro and specific antibody response to antigens were severely reduced. All immune defects, except those that affected B cell function, were absent in \(I \kappa B \alpha\) S32I mutant \(Rag2^{-/- }\) bone marrow chimeras, indicating that defects in non-lymphiod cells play a major role in the immunodeficiency of patients with ED-ID due to mutations in \(I \kappa B \alpha\). This has important clinical implications, as bone marrow transplant may not be able to correct immune function in such patients. The lessons learned in these chapters may be applicable to other mutations that impair \(NF\kappa B\) signaling and have important implications for the treatment of patients who carry these mutations.