RESUMO
BACKGROUND: Severe combined immunodeficiency (SCID) comprises a heterogeneous group of heritable deficiencies of humoral and cell-mediated immunity. Many patients with SCID have lymphocyte-activation defects that remain uncharacterized. METHODS: We performed genetic studies in four patients, from four families of Northern Cree ancestry, who had clinical characteristics of SCID, including early onset of severe viral, bacterial, and fungal infections despite normal B-cell and T-cell counts. Genomewide homozygosity mapping was used to identify a candidate region, which was found on chromosome 8; all genes within this interval were sequenced. Immune-cell populations, signal transduction on activation, and effector functions were studied. RESULTS: The patients had hypogammaglobulinemia or agammaglobulinemia, and their peripheral-blood B cells and T cells were almost exclusively of naive phenotype. Regulatory T cells and γδ T cells were absent. All patients carried a homozygous duplication--c.1292dupG in exon 13 of IKBKB, which encodes IκB kinase 2 (IKK2, also known as IKKß)--leading to loss of expression of IKK2, a component of the IKK-nuclear factor κB (NF-κB) pathway. Immune cells from the patients had impaired responses to stimulation through T-cell receptors, B-cell receptors, toll-like receptors, inflammatory cytokine receptors, and mitogens. CONCLUSIONS: A form of human SCID is characterized by normal lymphocyte development despite a loss of IKK2 function. IKK2 deficiency results in an impaired response to activation stimuli in a variety of immune cells, leading to clinically relevant impairment of adaptive and innate immunity. Although Ikk2 deficiency is lethal in mouse embryos, our observations suggest a more restricted, unique role of IKK2-NF-κB signaling in humans. (Funded by the German Federal Ministry of Education and Research and others.).
Assuntos
Agamaglobulinemia/genética , Quinase I-kappa B/genética , Mutação , Imunodeficiência Combinada Severa/genética , Imunidade Adaptativa/genética , Linfócitos B/fisiologia , Evolução Fatal , Feminino , Genes Recessivos , Humanos , Quinase I-kappa B/deficiência , Imunidade Inata/genética , Indígenas Norte-Americanos , Lactente , Recém-Nascido , Ativação Linfocitária , Contagem de Linfócitos , Masculino , Linhagem , Análise de Sequência de DNA , Linfócitos T/fisiologiaRESUMO
Group B streptococci, a major cause of sepsis, induce inflammatory cytokines in strict dependence on bacterial ssRNA and the host molecules MyD88 and UNC-93B. In this study, we show that NO plays an important role in Group B streptococci-induced transcriptional activation of cytokine genes. Phagocytosis induced NO in a MyD88-dependent fashion. In turn, NO propagated the acidification of phagosomes and the processing of phagosomal bacterial nucleic acids and was required for potent transcriptional activation of cytokine genes by streptococci. This NO-dependent amplification loop has important mechanistic implications for the anti-streptococcal macrophage response and sepsis pathogenesis.
Assuntos
Citocinas/biossíntese , Macrófagos/imunologia , Macrófagos/microbiologia , Óxido Nítrico/fisiologia , Processamento Pós-Transcricional do RNA/imunologia , RNA Bacteriano/metabolismo , Streptococcus agalactiae/imunologia , Animais , Linhagem Celular Transformada , Humanos , Recém-Nascido , Macrófagos/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Fator 88 de Diferenciação Mieloide/deficiência , Fator 88 de Diferenciação Mieloide/fisiologia , Óxido Nítrico/biossíntese , Óxido Nítrico Sintase Tipo II/deficiência , Óxido Nítrico Sintase Tipo II/genética , Fagocitose/imunologia , Fagossomos/imunologia , Fagossomos/microbiologia , Streptococcus agalactiae/genéticaRESUMO
The key step of protein N-glycosylation is catalyzed by the multimeric oligosaccharyltransferase complex (OST). Biochemical and genetic studies have revealed that OST from Saccharomyces cerevisiae consists of nine subunits: Wbp1, Swp1, Stt3, Ost1, Ost2, Ost3, Ost4, Ost5, and Ost6. With the exception of Stt3, assumed to contain the catalytic site, little is known about the function of other OST subunits. The existence of the OST complex is suggested to allow substrate specificity and efficient transfer, a close interaction with the translocon and the prevention of protein folding to ensure the efficient co-translational modification of proteins. However, in the recently completed genome of the trypanosomatid parasite Leishmania major STT3 (of which four paralogs exist, STT3-1, STT3-2, STT3-3, and STT3-4) is the only OST subunit that can be identified. Here we report that L.m.STT3 proteins, except STT3-3, are able to complement stt3 deficiency in yeast during vegetative growth, but only poorly during sporulation. By blue native electrophoresis we demonstrate that the L.mSTT3 is active mainly as a free, monomeric enzyme. In cell-free assays and also in vivo we find that L.mSTT3, expressed in yeast, has a broad specificity for nonglucosylated lipid-linked mannose-oligosaccharides, typical for several protists. But when incorporated into the OST complex, L.mSTT3 transfers also the common eukaryotic Glc(3)Man(9)GlcNAc(2)-PP-Dol donor. Finally, three L.m.STT3 paralogs were shown to complement not only stt3 but also ost1, ost2, wbp1, or swp1 mutants. Thus, STT3 from Leishmania can substitute for the whole OST complex.
Assuntos
Hexosiltransferases/genética , Leishmania major/enzimologia , Proteínas de Membrana/genética , Proteínas de Protozoários/genética , Proteínas de Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/enzimologia , Sequência de Aminoácidos , Animais , Glicosilação , Hexosiltransferases/metabolismo , Leishmania major/genética , Leishmania major/metabolismo , Proteínas de Membrana/metabolismo , Dados de Sequência Molecular , Complexos Multienzimáticos/genética , Complexos Multienzimáticos/metabolismo , Mutagênese Sítio-Dirigida , Proteínas de Protozoários/metabolismo , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Alinhamento de Sequência , Supressão GenéticaRESUMO
In this study, we investigated the impact of the cell membrane composition of E. faecalis on its recognition by the host immune system. To this end, we employed an E. faecalis deletion mutant (ΔbgsA) that does not synthesize the major cell membrane glycolipid diglycosyl-diacylglycerol (DGlcDAG). Proteomic analysis revealed that 13 of a total of 21 upregulated surface-associated proteins of E. faecalis ΔbgsA were lipoproteins. This led to a total lipoprotein content in the cell membrane of 35.8% in ΔbgsA compared to only 9.4% in wild-type bacteria. Increased lipoprotein content strongly affected the recognition of ΔbgsA by mouse macrophages in vitro with an increased stimulation of TNF-α production by heat-fixed bacteria and secreted antigens. Inactivation of the prolipoprotein diacylglycerol transferase (lgt) in ΔbgsA abrogated TNF-α induction by a ΔbgsA_lgt double mutant indicating that lipoproteins mediate increased activation of mouse macrophages by ΔbgsA. Heat-fixed ΔbgsA bacteria, culture supernatant, or cell membrane lipid extract activated transfected HEK cells in a TLR2-dependent fashion; the same was not true of wild-type bacteria. In mice infected intraperitoneally with a sublethal dose of E. faecalis we observed a 70% greater mortality in mice infected with ΔbgsA compared with wild-type-infected mice. Increased mortality due to ΔbgsA infection was associated with elevated plasma levels of the inflammatory cytokines TNF-α, IL-6 and MIP-2. In summary, our results provide evidence that an E. faecalis mutant lacking its major bilayer forming glycolipid DGlcDAG upregulates lipoprotein expression leading to increased activation of the host innate immune system and virulence in vivo.