Loss of T cell and B cell quiescence precedes the onset of microbial flora-dependent wasting disease and intestinal inflammation in Gimap5-deficient mice.

Homeostatic control of the immune system involves mechanisms that ensure the self-tolerance, survival and quiescence of hematopoietic-derived cells. In this study, we demonstrate that the GTPase of immunity associated protein (Gimap)5 regulates these processes in lymphocytes and hematopoietic progenitor cells. As a consequence of a recessive N-ethyl-N-nitrosourea-induced germline mutation in the P-loop of Gimap5, lymphopenia, hepatic extramedullary hematopoiesis, weight loss, and intestinal inflammation occur in homozygous mutant mice. Irradiated fetal liver chimeric mice reconstituted with Gimap5-deficient cells lose weight and become lymphopenic, demonstrating a hematopoietic cell-intrinsic function for Gimap5. Although Gimap5-deficient CD4(+) T cells and B cells appear to undergo normal development, they fail to proliferate upon Ag-receptor stimulation although NF-kappaB, MAP kinase and Akt activation occur normally. In addition, in Gimap5-deficient mice, CD4(+) T cells adopt a CD44(high)CD62L(low)CD69(low) phenotype and show reduced IL-7ralpha expression, and T-dependent and T-independent B cell responses are abrogated. Thus, Gimap5-deficiency affects a noncanonical signaling pathway required for Ag-receptor-induced proliferation and lymphocyte quiescence. Antibiotic-treatment or the adoptive transfer of Rag-sufficient splenocytes ameliorates intestinal inflammation and weight loss, suggesting that immune responses triggered by microbial flora causes the morbidity in Gimap5-deficient mice. These data establish Gimap5 as a key regulator of hematopoietic integrity and lymphocyte homeostasis.

An Slfn2 mutation causes lymphoid and myeloid immunodeficiency due to loss of immune cell quiescence.

Here we describe a previously unknown form of inherited immunodeficiency revealed by an N-ethyl-N-nitrosourea-induced mutation called elektra. Mice homozygous for this mutation showed enhanced susceptibility to bacterial and viral infection and diminished numbers of T cells and inflammatory monocytes that failed to proliferate after infection and died via the intrinsic apoptotic pathway in response to diverse proliferative stimuli. They also had a greater proportion of T cells poised to replicate DNA, and their T cells expressed a subset of activation markers, suggestive of a semi-activated state. We positionally ascribe the elektra phenotype to a mutation in the gene encoding Schlafen-2 (Slfn2). Our findings identify a physiological role for Slfn2 in the defense against pathogens through the regulation of quiescence in T cells and monocytes.

A mutation of Ikbkg causes immune deficiency without impairing degradation of IkappaB alpha.

Null alleles of the gene encoding NEMO (NF-kappaB essential modulator) are lethal in hemizygous mice and men, whereas hypomorphic alleles typically cause a syndrome of immune deficiency and ectodermal dysplasia. Here we describe an allele of Ikbkg in mice that impaired Toll-like receptor signaling, lymph node formation, development of memory and regulatory T cells, and Ig production, but did not cause ectodermal dysplasia. Degradation of IkappaB alpha, which is considered a primary requirement for NEMO-mediated immune signaling, occurred normally in response to Toll-like receptor stimulation, yet ERK phosphorylation and NF-kappaB p65 nuclear translocation were severely impaired. This selective loss of function highlights the immunological importance of NEMO-regulated pathways beyond IkappaB alpha degradation, and offers a biochemical explanation for rare immune deficiencies in man.

The Tpl2 mutation Sluggish impairs type I IFN production and increases susceptibility to group B streptococcal disease.

Sluggish was identified in a population of third generation mice descended from N-ethyl-N-nitrosourea-mutagenized sires. Macrophages from homozygotes exhibited impaired TNF-alpha production in response to all TLR ligands tested and displayed impaired type I IFN production in response to TLR7 and TLR9 stimulations. The phenotype was confined to a critical region on mouse chromosome 18 and then ascribed to a T to A transversion in the acceptor splice site of intron 4 at position 13346 of the Map3k8 gene, resulting in defective splicing. The Map3k8(Sluggish) mutation does not result in susceptibility to viral infections, but Sluggish mice displayed high susceptibility to group B streptococcus infection, with impaired TNF-alpha and type I IFN production in infected macrophages. Our data demonstrate that the encoded protein kinase Tpl2 plays an essential role in cell signaling in the immune response to certain pathogens.

Mice with mutations of Dock7 have generalized hypopigmentation and white-spotting but show normal neurological function.

The classical recessive coat color mutation misty (m) arose spontaneously on the DBA/J background and causes generalized hypopigmentation and localized white-spotting in mice, with a lack of pigment on the belly, tail tip, and paws. Here we describe moonlight (mnlt), a second hypopigmentation and white-spotting mutation identified on the C57BL/6J background, which yields a phenotypic copy of m/m coat color traits. We demonstrate that the 2 mutations are allelic. m/m and mnlt/mnlt phenotypes both result from mutations that truncate the dedicator of cytokinesis 7 protein (DOCK7), a widely expressed Rho family guanine nucleotide exchange factor. Although Dock7 is transcribed at high levels in the developing brain and has been implicated in both axon development and myelination by in vitro studies, we find no requirement for DOCK7 in neurobehavioral function in vivo. However, DOCK7 has non-redundant role(s) related to the distribution and function of dermal and follicular melanocytes.

The serine protease TMPRSS6 is required to sense iron deficiency.

Hepcidin, a liver-derived protein that restricts enteric iron absorption, is the key regulator of body iron content. Several proteins induce expression of the hepcidin-encoding gene Hamp in response to infection or high levels of iron. However, mechanism(s) of Hamp suppression during iron depletion are poorly understood. We describe mask: a recessive, chemically induced mutant mouse phenotype, characterized by progressive loss of body (but not facial) hair and microcytic anemia. The mask phenotype results from reduced absorption of dietary iron caused by high levels of hepcidin and is due to a splicing defect in the transmembrane serine protease 6 gene Tmprss6. Overexpression of normal TMPRSS6 protein suppresses activation of the Hamp promoter, and the TMPRSS6 cytoplasmic domain mediates Hamp suppression via proximal promoter element(s). TMPRSS6 is an essential component of a pathway that detects iron deficiency and blocks Hamp transcription, permitting enhanced dietary iron absorption.