Phosphorylated STAT1 (pSTAT1) dissociates from the interferon receptor-JAK complex, dimerizes, and translocates to the nucleus where it drives gene transcription.2 Loss-of-function mutations in STAT1 ...are associated with intracellular bacterial and viral infections, whereas gain-of-function (GOF) mutations result mainly in chronic mucocutaneous candidiasis with autoimmunity, viral infections, and delayed shedding of deciduous teeth.3-6 GOF mutations have been identified in the coiled-coil domain and DNA-binding domain of STAT1. The mutation was predicted to be benign (score of 0.238) by PolyPhen-2 and tolerated (score of 1.00) by SIFT. Because the features of the patient's phenotype were shared with patients with reported STAT1 GOF mutations (see Table E2 in this article's Online Repository at www.jacionline.org for a comprehensive comparison with other patients with GOF mutations in STAT1), we examined whether her mutation acts as a GOF mutation.
To the Editor: Inducible T-cell costimulator (ICOS) is a costimulatory receptor upregulated on activated T cells.1ICOS mutations have been identified in 11 patients, 9 of whom share the same ...mutation.2 These patients have a common variable immunodeficiency (CVID) phenotype, with recurrent sinopulmonary and gastrointestinal infections, autoimmunity, inflammatory bowel disease, and granulomatous disease.1 ICOS deficiency is characterized by defective class-switching with hypogammaglobulinemia, absent antigen responses, and impaired germinal center formation.2 We report a novel ICOS mutation resulting in opportunistic infections and colitis responsive to hematopoietic stem cell transplant (HSCT). Myeloid-derived dendritic cells contribute to microbial surveillance in the gastrointestinal tract and express both ICOS and ICOSL, an interaction critical for the cytokine response to nucleotide-binding oligomerization domain 2 and Toll-like receptor stimulation.12 Furthermore, an ICOSL polymorphism (rs7282490) is associated with reduced ICOSL expression, decreased nucleotide-binding oligomerization domain 2-mediated signaling, and an increased risk of Crohn disease.
Background Wiskott-Aldrich syndrome protein (WASP) links T-cell receptor (TCR) signaling to the actin cytoskeleton. WASP is normally protected from degradation by the Ca++ -dependent protease calpain ...and by the proteasome because of its interaction with the WASP-interacting protein. Objective We investigated whether WASP is degraded after TCR ligation and whether its degradation downregulates F-actin assembly caused by TCR ligation. Methods Primary T cells, Jurkat T cells, and transfected 293T cells were used in immunoprecipitation experiments. Intracellular F-actin content was measured in splenic T cells from wild-type, WASP-deficient, and c–Casitas B-lineage lymphoma (Cbl)-b–deficient mice by using flow cytometry. Calpeptin and MG-132 were used to inhibit calpain and the proteasome, respectively. Results A fraction of WASP in T cells was degraded by calpain and by the ubiquitin-proteasome pathway after TCR ligation. The Cbl-b and c-Cbl E3 ubiquitin ligases associated with WASP after TCR signaling and caused its ubiquitination. Inhibition of calpain and lack of Cbl-b resulted in a significantly more sustained increase in F-actin content after TCR ligation in wild-type T cells but not in WASP-deficient T cells. Conclusion TCR ligation causes WASP to be degraded by calpain and to be ubiquitinated by Cbl family E3 ligases, which targets it for destruction by the proteasome. WASP degradation might provide a mechanism for regulating WASP-dependent TCR-driven assembly of F-actin.
Background Atopic dermatitis (AD) is characterized by local and systemic TH 2 responses to cutaneously introduced allergens and is a risk factor for asthma. Blockade of TH 2 cytokines has been ...suggested as therapy for AD. Objectives We sought to examine the effect of the absence of IL-4 and IL-13 on the TH 17 response to epicutaneous sensitization in a murine model of allergic skin inflammation with features of AD. Methods Wild-type, IL4 knockout (KO), IL13 KO and IL4/13 double KO (DKO) mice were subjected to epicutaneous sensitization with ovalbumin (OVA) or saline and airway challenged with OVA. Systemic immune responses to OVA, skin and airway inflammation, and airway hyperresponsiveness were examined. Results OVA-sensitized DKO mice exhibited impaired TH 2-driven responses with undetectable OVA-specific IgE levels and severely diminished eosinophil infiltration at sensitized skin sites but intact dermal infiltration with CD4+ cells. DKO mice mounted exaggerated IL-17A but normal IFN-γ and IL-5 systemic responses. Airway challenge of these mice with OVA caused marked upregulation of IL-17 mRNA expression in the lungs, increased neutrophilia in bronchoalveolar lavage fluid, airway inflammation characterized by mononuclear cell infiltration with no detectable eosinophils, and bronchial hyperresponsiveness to methacholine that were reversed by IL-17 blockade. IL-4, but not IL-13, was identified as the major TH 2 cytokine that downregulates the IL-17 response in epicutaneously sensitized mice. Conclusion Epicutaneous sensitization in the absence of IL-4/IL-13 induces an exaggerated TH 17 response systemically and in lungs after antigen challenge that results in airway inflammation and airway hyperresponsiveness.
Background Transmembrane activator, calcium modulator, and cyclophilin ligand interactor (TACI) expression on B cells is upregulated by Toll-like receptor (TLR) 4. Objective We sought to examine ...whether TACI synergizes with TLR4 in driving immunoglobulin production by B cells and to examine the mechanism of this synergy. Methods Purified mouse naive B cells were stimulated with the TACI ligand a proliferation-inducing ligand (APRIL) and with suboptimal concentrations of the TLR4 ligand LPS in the presence or absence of IL-4. Immunoglobulin secretion was measured by means of ELISA. Surface IgG1–positive B cells and CD138+ plasmacytoid cells were enumerated by means of FACS. Expression of γ1 and ϵ germline transcripts, activation-induced cytidine deaminase, and γ1 and ϵ mature transcripts was measured by means of RT-PCR. Results APRIL synergized with LPS in driving B-cell proliferation and IgM, IgG1, IgG3, IgE, and IgA production. This was mediated by TACI because it was preserved in B-cell maturation antigen−/− , but not TACI−/− , B cells. APRIL and LPS synergized to promote isotype switching, as evidenced by increased expression of activation-induced cytidine deaminase and γ1 and ϵ mature transcripts and generation of surface IgG1–positive cells. More importantly, APRIL and LPS strongly synergized to drive the plasma cell differentiation program, as evidenced by an increase in CD138+ cells and expression of B lymphocyte induced maturation protein-1 (Blimp-1), interferon regulatory factor-4 (IRF-4), and the spliced form of X-box binding protein-1 (XBP-1). TACI−/− mice had impaired IgM and IgG1 antibody responses to immunization, with a suboptimal dose of the type I T cell–independent antigen 2, 4, 6- Trinitrophenol (TNP)-LPS. Conclusions These observations suggest that TACI cooperates with TLR4 to drive B-cell differentiation and immunoglobulin production in vitro and in vivo.
Most patients with ALPS harbor deleterious Fas mutations; however, a small number of patients carry homozygous FasL mutations that abolish protein expression or activity3-5 or heterozygous FasL ...mutations that exert a dominant negative effect.6,7 It is possible that Fas is located in a mutational hotspot and/or that autosomal-recessive FasL deficiency may be underdiagnosed if it occurs primarily in countries with a high incidence of consanguineous unions but limited diagnostic facilities. Laboratory values Patient 1low * (7 mo) Patient 2dagger (3 mo) Lymphocyte numbers (cells/μL) 4,410 (2,320-5,490) 2,740 (1,880-5,390) CD3+ 3,006 (1,900-6,200) 2,065 (2,500-5600) CD3+CD4+ 1,439 (1,400-4,300) 998 (1,600-4,000) CD3+CD8+ 813 (500-1,700) 772 (500-1,700) CD4+/CD8+ ratio 1.77 (1.3-3.9) 1.29 (1.3-3.9) Naive CD3+CD4+CD45RA (% of CD4) 61.5 (50-85) ND Memory CD3+CD4+CD45RO (% of CD4) 38.5 (15-50) ND Naive CD3+CD8+CD45RA (% of CD8) 65.9 (50-85) ND Memory CD3+CD8+CD45RO (% of CD8) 34.1 (15-50) ND CD3+TCRα/β+CD4-CD8- (% of CD3TCRα/β) 20.7 (<2) 14.4 (<2) CD3+TCRγ/δ+ (% of CD3) 10.4 (<12) 7.1 (<12) CD19+ 798 (610-2,600) 158 (430-3,000) CD16+/CD56+ 560 (160-1,100) 201 (160-1,100) Immunoglobulins (mg/dL) IgG 3,157 (300-1,500) ND IgA 299 (16-100) ND IgM 54 (25-115) ND IgE 866 (0-30) ND Proliferation (cpm) PHA 45,810 (64,561) 23,842 (43,550) Anti-CD3 mAb 30,853 (46,958) 27,016 (51,515) Table EI Immunophenotype of patients 1 and 2 ND, Not determined.The age-matched normal ranges (shown in parentheses) for lymphocyte numbers and immunoglobulin concentrations are from Morbach et al,E1 Piatosa et al,E2 Shearer et al,E3 and Jolliff et al.E4 Lymphocyte proliferation, expressed as radioactive counts per minute (cpm), was measured by 3H-thymidine incorporation into DNA from the patient and a normal healthy control (shown in parentheses) studied the same day as the patient.
Background Cutaneous prostaglandin (PG) D2 levels increase after scratching. Chemoattractant receptor–homologous molecule expressed on receptor on TH 2 cells (CRTH2) mediates chemotaxis to PGD2 and ...is expressed on TH 2 cells and eosinophils, which infiltrate skin lesions in patients with atopic dermatitis. Objective We sought to examine the role of CRTH2 in a murine model of atopic dermatitis. Methods CRTH2−/− mice and wild-type control animals were epicutaneously sensitized by means of repeated application of ovalbumin (OVA) to tape-stripped skin for 7 weeks and then challenged by means of OVA application to tape-stripped previously unsensitized skin for 1 week. Skin histology was assessed by means of hematoxylin and eosin staining and immunohistochemistry. Cytokine mRNA expression was examined by means of quantitative RT-PCR. Levels of PGD2 , antibody, and cytokines were measured by means of ELISA. Results PGD2 levels significantly increased in skin 24 hours after tape stripping, although not in skin subjected to repeated sensitization with OVA. Allergic skin inflammation developed normally at sites of chronic epicutaneous sensitization with OVA in CRTH2−/− mice but was severely impaired in previously unsensitized skin challenged with OVA, as evidenced by significantly decreased skin infiltration with eosinophils and CD4+ cells and impaired TH 2 cytokine mRNA expression. Impaired skin inflammation at sites of acute OVA challenge in CRTH2−/− mice was not due to an impaired systemic response to epicutaneous sensitization because OVA-specific IgG1 and IgE antibody levels and OVA-driven splenocyte secretion of cytokines in these mice were comparable with those seen in wild-type control animals. Conclusions CRTH2 promotes allergic skin inflammation in response to cutaneous exposure to antigen in previously sensitized mice.
Complete deficiency of either RAG1 or RAG2 results in classical severe combined immunodeficiency lacking T and B cells, since RAG1 mediates DNA binding and cleavage, while RAG2 is an essential ...cofactor for RAG1 function.1 Hypomorphic missense mutations that preserve residual RAG activity and allow the development of oligoclonal T cells, but virtually no B cells, result in recurrent infections, erythroderma, hepatomegaly, colitis, and αβ T-cell expansion (Omenn syndrome).2RAG1/2 mutations can also cause γδ T-cell expansion and immunodeficiency with granulomas.3 Hyper-IgM syndrome is characterized by normal or increased IgM levels with decreased IgG and IgA levels. Because her phenotype was consistent with Omenn syndrome, RAG1 and RAG2 were sequenced.
Background TNFRSF13B , which encodes transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), is mutated in 10% of patients with common variable immunodeficiency. One ...of the 2 most common TACI mutations in common variable immunodeficiency, C104R, abolishes ligand binding and is found predominantly in the heterozygous state. The murine TACI mutant C76R is the equivalent of the human TACI mutant C104R. Objective We sought to define the consequence of the C76R mutation on TACI function in mice that express both wild-type TACI and the murine C76R mutant. Methods Transgenic mice that express murine TACI C76R, the counterpart of human TACI C104R, on the TACI+/− B6/129 background (C76R/TACI+/− mice) were constructed. Serum immunoglobulins and antibody responses to the type II T-independent antigen trinitrophenylated (TNP)-Ficoll were determined by means of ELISA. B-cell proliferation in response to a proliferation-inducing ligand was determined based on tritiated thymidine incorporation into DNA. IgG1 secretion by B cells in response to a proliferation-inducing ligand plus IL-4 was determined by means of ELISA. Results C76R/TACI+/− mice had significantly impaired antibody responses to the type II T-independent antigen TNP-Ficoll compared with TACI+/+ B6/129 control animals, and their B cells were impaired in their capacity to proliferate and secrete IgG1 in response to TACI ligation. Unexpectedly, TACI+/− mice had similarly impaired B-cell function as C76R/TACI+/− littermates. Impaired TACI function caused by haploinsufficiency was confirmed in TACI+/− mice on the C57BL/6 background. Conclusion These results suggest that the human TACI mutant C104R might impair TACI function in heterozygotes through haploinsufficiency.
PDF
