Phenotypic perturbation of B cells in the Wiskott-Aldrich syndrome.

Wiskott-Aldrich syndrome (WAS) is an X-linked immunodeficiency/platelet disease due to mutations of WASP, a cytoskeletal regulatory protein of blood cells. Patients exhibit a range of immune defects generally attributed to defective T-cell function, including poor response to immunization, skewed immunoglobulin isotypes, eczema, recurrent infections, autoimmune disease and increased frequency of malignancies. Here we show a deficit of total B-cells in WAS patients of various ages and identify phenotypic perturbations involving complement receptors and CD27. Whereas B-cells of normal healthy donors are overwhelmingly CD21/CD35-positive, B-cells expressing these receptors are significantly reduced in number in WAS patients, and their paucity may cause suboptimal antigen capture and presentation. The frequencies of IgD(-) and IgG(+) patient B-cells were not different from healthy donors (although absolute numbers were decreased), indicating that isotype switching is occurring. In contrast, the frequency of cells positive for CD27, the marker of post germinal centre B-cells, was significantly decreased even among isotype-switched cells, and B-cells resembling germinal centre progenitors (CD10(+)CD27(-)CD38(bright)) were more frequent in adult patients, suggesting impaired germinal centre maturation/differentiation. The documentation of these phenotypic perturbations and deficit of total cells suggest that defects intrinsic to B-cells contribute to the impaired humoral immunity that characterizes this disease.

Early deficit of lymphocytes in Wiskott-Aldrich syndrome: possible role of WASP in human lymphocyte maturation.

Wiskott-Aldrich syndrome (WAS) is an X-linked platelet/immunodeficiency disease. The affected gene encodes WASP, a multidomain protein that regulates cytoskeletal assembly in blood cells. Patients have recurring infections, and their lymphocytes exhibit deficient proliferative responses in vitro. We report an evaluation of peripheral blood lymphocytes of 27 WAS patients, aged one month to 55 years. Whereas NK cells were normal, a significant deficit of T and B lymphocytes was observed. The number of lymphocytes was already decreased in infant patients, suggesting deficient output. Both CD4 and CD8 T lymphocytes were affected; the decrease was most pronounced for naïve T cells. Naïve CD4 lymphocytes of patients showed normal expression of Bcl-2, and Ki-67, and normal survival in vitro, suggesting that their in vivo survival and proliferation are normal. The collective data suggest that the patients' lymphocyte deficit results from deficient output, likely due to abnormal lymphocyte maturation in the thymus and bone marrow. We propose that WASP plays an important role not only in the function of mature T lymphocytes, but also in the maturation of human T and B lymphocytes and that impaired lymphocyte maturation is central to the aetiology of WAS immunodeficiency.

A novel protocol to identify mutations in patients with wiskott-Aldrich syndrome.

Mutations of WASP (Wiskott-Aldrich syndrome protein) underlie the severe immunodeficiency/platelet disorder Wiskott-Aldrich syndrome (WAS) and its milder variant X-linked thrombocytopenia (XLT). The affected gene, a 12-exon structure on the X-chromosome, is expressed exclusively in blood cells. The encoded product WASP is a 502-amino-acid scaffolding protein that functions in stimulus-induced nucleation of actin filaments to form dynamic cell surface projections. To date, more than 150 mutations have been identified in 300 WAS/XLT kindred worldwide, generally through methodologies that include sophisticated exon screening steps such as single-strand conformation analysis. We report here a simpler protocol, which was designed for use in clinical settings to identify the mutations of newly diagnosed patients. The approach relies on directly sequencing amplified exons according to a staggered schedule based on statistical evaluation of previous cases. In a 2 1/2-year trial, samples from 28 consecutive patients were analyzed; these included 3 "blindly labeled" previously studied cases. The mutations that were identified include a broad spectrum (8 missense, 3 nonsense, 5 splice site mutations, 11 small insertion/deletions, 1 large deletion) and were broadly distributed (in 10 of the 12 exons). All mutations were verified and no discrepancies were encountered. Per patient, a mean of six DNA sequencing reactions and 6-7 h of staff effort sufficed for mutation identification and verification, indicating that the protocol is cost-effective. This cumulative experience demonstrates the suitability, reliability, and versatility of the new protocol.

WASP and N-WASP in human platelets differ in sensitivity to protease calpain.

Mutations of Wiskott-Aldrich syndrome protein (WASP) underlie the severe thrombocytopenia and immunodeficiency of the Wiskott-Aldrich syndrome. WASP, a specific blood cell protein, and its close homologue, the broadly distributed N-WASP, function in dynamic actin polymerization processes. Here it is demonstrated that N-WASP is expressed along with WASP, albeit at low levels, in human blood cells. The presence of approximately 160 nmol/L rapidly acting N-WASP molecules may explain the normal capacity of WASP-negative patient platelets for early agonist-induced aggregation and filopodia formation. Ex vivo experiments revealed a significant difference between WASP and N-WASP in sensitivity to calpain, the Ca++-dependent protease activated in agonist-stimulated platelets. Through the use of a series of calpain-containing broken cell systems, it is shown that WASP is cleaved in a Ca++-dependent reaction inhibitable by calpeptin and E64d and that N-WASP is not cleaved, suggesting that the cleavage of WASP by calpain functions in normal platelets as part of a Ca++-dependent switch mechanism that terminates the surface projection phase of blood cell activation processes.

N-WASP deficiency reveals distinct pathways for cell surface projections and microbial actin-based motility.

The Wiskott-Aldrich syndrome protein (WASP) family of molecules integrates upstream signalling events with changes in the actin cytoskeleton. N-WASP has been implicated both in the formation of cell-surface projections (filopodia) required for cell movement and in the actin-based motility of intracellular pathogens. To examine N-WASP function we have used homologous recombination to inactivate the gene encoding murine N-WASP. Whereas N-WASP-deficient embryos survive beyond gastrulation and initiate organogenesis, they have marked developmental delay and die before embryonic day 12. N-WASP is not required for the actin-based movement of the intracellular pathogen Listeria but is absolutely required for the motility of Shigella and vaccinia virus. Despite these distinct defects in bacterial and viral motility, N-WASP-deficient fibroblasts spread by using lamellipodia and can protrude filopodia. These results imply a crucial and non-redundant role for N-WASP in murine embryogenesis and in the actin-based motility of certain pathogens but not in the general formation of actin-containing structures.

Cdc42 is required for PIP(2)-induced actin polymerization and early development but not for cell viability.

BACKGROUND: Cdc42 and other Rho GTPases are conserved from yeast to humans and are thought to regulate multiple cellular functions by inducing coordinated changes in actin reorganization and by activating signaling pathways leading to specific gene expression. Direct evidence implicating upstream signals and components that regulate Cdc42 activity or for required roles of Cdc42 in activation of downstream protein kinase signaling cascades is minimal, however. Also, whereas genetic analyses have shown that Cdc42 is essential for cell viability in yeast, its potential roles in the growth and development of mammalian cells have not been directly assessed. RESULTS: To elucidate potential functions of Cdc42 mammalian cells, we used gene-targeted mutation to inactivate Cdc42 in mouse embryonic stem (ES) cells and in the mouse germline. Surprisingly, Cdc42-deficient ES cells exhibited normal proliferation and phosphorylation of mitogen- and stress-activated protein kinases. Yet Cdc42 deficiency caused very early embryonic lethality in mice and led to aberrant actin cytoskeletal organization in ES cells. Moreover, extracts from Cdc42-deficient cells failed to support phosphatidylinositol 4,5-bisphosphate (PIP(2))-induced actin polymerization. CONCLUSIONS: Our studies clearly demonstrate that Cdc42 mediates PIP(2)-induced actin assembly, and document a critical and unique role for Cdc42 in this process. Moreover, we conclude that, unexpectedly, Cdc42 is not necessary for viability or proliferation of mammalian early embryonic cells. Cdc42 is, however, absolutely required for early mammalian development.

WASP levels in platelets and lymphocytes of wiskott-aldrich syndrome patients correlate with cell dysfunction.

Wiskott-Aldrich syndrome, an inherited blood cell disorder due to mutations of the X-chromosome gene WASP (Wiskott-Aldrich syndrome protein), was characterized originally by thrombocytopenia, immunodeficiency, and eczema. Whereas platelet dysfunction is severe and consistent, immune defects are clinically variable, ranging from negligible to life threatening. To understand this heterogeneity, we quantified WASP in PBMC and platelets, and also in neutrophils, of patients with diverse mutations. A surprisingly complex pattern of WASP expression found for lymphoid cells formed the basis for dividing the patient mutations into four groups. Group A have low WASP levels in PBMC and higher levels in EBV cell lines, as well as near normal WASP RNA levels (7 patients, most with mild disease), suggesting that group A WASP molecules are hypersusceptible to proteolysis. Group B have low WASP levels in PBMC and EBV cells and similar low RNA levels (2 patients, moderate disease). Group C have discordant expression: WASP-positive peripheral T cells and WASP-negative peripheral B cells and EBV cell lines (9 patients, variable disease severity). Noteworthy among group C kindred are several instances of B cell lymphomas. In group D, PBMC and EBV cell lines are WASP negative (7 patients, severe disease). In contrast to the complex lymphoid cell expression patterns, all patient platelets examined were WASP negative (18 diverse patients). WASP absence in platelets provides an apparent molecular explanation for the universally severe platelet dysfunction in this disease, and the cumulative lymphoid cell findings suggest that WASP levels play a substantial role in determining immune outcome.

Pathological events in platelets of Wiskott-Aldrich syndrome patients.

The Wiskott-Aldrich syndrome (WAS) is a severe X-linked platelet/immunological disorder arising from mutations of the gene WASP. At the clinical level, the major platelet abnormalities are small size and low number, both partially correctable by splenectomy. To identify underlying pathological events, we examined WAS platelets at various stages of their lifetime. In spleen sections from WAS patients, fluorescence microscopy showed dramatic co-localization of markers of platelets (CD41) and macrophages (CD68) compared to non-thrombocytopenic controls, suggesting that WAS splenic macrophages are involved in platelet removal. Study of isolated WAS blood platelets by flow cytometry showed substantial enhancement of surface exposure of phosphatidylserine (PS), a signal for engulfment by macrophages. Isolated resting WAS platelets were also aberrantly susceptible to microparticle release, and plasma samples of WAS patients contained > 5 times normal numbers of platelet-derived microparticles which may explain the small size of circulating platelets. Measurements with the Ca2+ sensitive dye fluo-3 revealed significantly increased Ca2+ levels, 310 +/- 13 nmol/l for WAS platelets versus 106 +/- 12 nmol/l for normal platelets, and also prolongation of agonist-induced Ca2+ flux. Cumulatively, these studies identify abnormal events occurring in WAS platelets: increased Ca2+ levels and enhancement of two Ca2+ dependent processes, PS exposure and microparticle release; these abnormal events may contribute to the in vivo decrease of platelet number and reduction of platelet size in this disease.

Endoscopic surgical management of sphenoid sinus disease.

OBJECTIVES: To assess the outcome of functional endoscopic sphenoid sinus surgery, and to determine the predictors of outcome. STUDY DESIGN: Retrospective chart review of 651 consecutive endoscopic sinus procedures performed between 1992 and 1997. SETTING: USC University Hospital, University of Southern California, Los Angeles. MATERIALS AND METHODS: Seventy-four patients (11.4% of all endoscopic procedures) with sphenoid sinus disease were selected. All 74 patients were mailed a sinusitis-specific questionnaire, and 46 of them (62.2%) responded. Outcome measures derived from clinician ratings were applied to all 74 patients, and those derived from self-report were applied to 46. Outcome measures were determined from patient questionnaires at a minimum of 6-month postoperative follow-up, operative complications, and clinician perceptual ratings. Patient questionnaires addressed general patient satisfaction, symptom score, and medication usage. A statistical analysis was performed using chi2 test, linear regression, and one-way nonparametric ANOVA. RESULTS: Favorable surgical outcomes based on general patient satisfaction (84.8%, n = 39) and clinician perceptual rating (78.4%, n = 58) were noted. Minor postoperative complications were noted in 10 patients (13.5%) and 8 patients (10.8%) needed revision endoscopic procedures during follow-up. Of the complications, eight (80%) occurred in revision endoscopic procedures. The use of an expanded, sinus-specific symptom score revealed far fewer favorable outcomes (56.5%, n = 26). Seven outcome predictors were established, although none of the predictors held for more than one of the six outcome measures used. CONCLUSION: Endoscopic sphenoid sinus surgery is safe and effective. An expanded symptom score is recommended to assess the outcome of this procedure.

The cytoskeletal linker protein moesin: decreased levels in Wiskott-Aldrich syndrome platelets and identification of a cleavage pathway in normal platelets.

The Wiskott-Aldrich syndrome (WAS) is a severe disease of platelets (small size, thrombocytopenia) and lymphocytes (immunodeficiency) arising from mutations of the X-chromosome gene WASP. Because of the prominent role of cytoskeletal abnormalities, particularly the paucity of surface microvilli, in the cellular pathology of this disease, blood cells from WAS patients were examined for moesin, a cytoskeletal linker protein that stabilizes cell surface microvilli, filopodia and lamellipodia. Comparison of patient and normal lymphocytes by immunofluorescence microscopy and immunoblotting showed normal levels and distribution of moesin in lymphocytes of WAS patients. In contrast, platelets from WAS patients stained only dimly for moesin relative to normal platelets. Quantitation by immunoblot revealed significantly decreased moesin levels in WAS patient platelets relative to normal platelets (63.5 +/- 4.9% of normal levels, n = 8, P < 0.0001). A novel reaction of normal platelets was discovered that may play a role in the depletion of moesin in patient platelets, namely the cleavage of moesin as a late event in platelet activation in response to certain platelet agonists.

The Wiskott-Aldrich syndrome protein (WASP): roles in signaling and cytoskeletal organization.

The Wiskott-Aldrich Syndrome (WAS) is a rare X-linked primary immunodeficiency that is characterized by recurrent infections, hematopoietic malignancies, eczema, and thrombocytopenia. A variety of hematopoietic cells are affected by the genetic defect, including lymphocytes, neutrophils, monocytes, and platelets. Early studies noted both signaling and cytoskeletal abnormalities in lymphocytes from WAS patients. Following the identification of WASP, the gene mutated in patients with this syndrome, and the more generally expressed WASP homologue N-WASP, studies have demonstrated that WASP-family molecules associate with numerous signaling molecules known to alter the actin cytoskeleton. WASP/N-WASP may depolymerize actin directly and/or serve as an adaptor or scaffold for these signaling molecules in a complex cascade that regulates the cytoskeleton.

Wiskott-Aldrich syndrome protein-deficient mice reveal a role for WASP in T but not B cell activation.

The Wiskott-Aldrich syndrome (WAS) is a human X-linked immunodeficiency resulting from mutations in a gene (WASP) encoding a cytoplasmic protein implicated in regulating the actin cytoskeleton. To elucidate WASP function, we disrupted the WASP gene in mice by gene-targeted mutation. WASP-deficient mice showed apparently normal lymphocyte development, normal serum immunoglobulin levels, and the capacity to respond to both T-dependent and T-independent type II antigens. However, these mice did have decreased peripheral blood lymphocyte and platelet numbers and developed chronic colitis. Moreover, purified WASP-deficient T cells showed markedly impaired proliferation and antigen receptor cap formation in response to anti-CD3epsilon stimulation. Yet, purified WASP-deficient B cells showed normal responses to anti-Ig stimulation. We discuss the implications of our findings regarding WASP function in receptor signaling and cytoskeletal reorganization in T and B cells and compare the effects of WASP deficiency in mice and humans.

A randomized, controlled trial to study the efficacy and safety of C1 inhibitor concentrate in treating hereditary angioedema.

BACKGROUND: No effective treatment exists in the United States for acute attacks of hereditary angioedema (HAE). STUDY DESIGN AND METHODS: To evaluate the efficacy and safety of C1 inhibitor concentrate in treating HAE, a large primary care and referral center hospital conducted a randomized, placebo-controlled, double-blind trial with intent-to-treat analysis. Of the 36 patients enrolled in the study, 23 received treatment, and 22 completed the trial. C1 inhibitor concentrate or albumin (placebo) infusions were administered in a blind fashion to HAE patients who came to the hospital for treatment no later than 5 hours after an attack began. RESULTS: Relief was almost twice as fast in persons receiving C1 inhibitor concentrate than in the controls: 7.62 hours (mean; SD 7.08) versus 15.35 hours (mean; SD 8.31), respectively. The difference for time-to-relief was highly significant (p = 0.007, Mann-Whitney U test). The median time-to-relief was 6.17 hours (interquartile range 0.33-15.35) in the treatment group and 15.35 hours (interquartile range 14.00-22.83) in the control group. Resolution of symptoms was one-third faster in the C1 inhibitor concentrate group than in the placebo group: 23.98 hours (mean; SD 14.81) and 34.58 hours (mean; SD 13.56), respectively (p = 0.09, Mann-Whitney U test). Recovery of functional C1 inhibitor was 119.65 percent (mean; SD 50.80), and half-life was 37.87 hours (mean; SD 19.75). Recovery of antigenic C1 inhibitor was 147.75 percent (mean; SD 97.68), and half-life was 24.01 hours (mean; SD 9.70). There were no viral infections or serious adverse effects from the drug after 70 attacks in the treatment group and 96 attacks in the control group. CONCLUSIONS: C1 inhibitor concentrate is a safe, effective treatment for acute attacks of HAE.

Endotoxin shock in antibody-deficient mice: unraveling the role of natural antibody and complement in the clearance of lipopolysaccharide.

While the significance of natural Ab is not entirely clear, one proposed role is clearance of bacterial Ags. To determine whether natural Ab was involved in clearance of endotoxin, we have examined novel strains of mice with either a total or selective deficiency in Ig. Recombinase-activating gene-2 (RAG-2(-/-))-deficient mice, which have no serum Ig due to arrested development of B cells at the pro-B stage, demonstrate increased sensitivity to endotoxin that correlates with an impaired clearance. When RAG-2(-/-) mice are reconstituted with pooled sera from normal mice, both survival and clearance of circulating endotoxin are enhanced. To further define the nature of the protective Ab, Bruton's tyrosine kinase (Btk)-deficient mice were characterized in the high dose LPS model. Like RAG-2(-/-) mice, they are highly sensitive to endotoxin and have an impaired clearance of LPS. Reconstitution of Btk(-/-) mice, which have reduced levels of IgG3 and IgM, with purified normal mouse IgM dramatically enhances their ability to clear endotoxin compared with mock (saline)-reconstituted littermates. The cellular source of natural anti-LPS IgM was identified as the peritoneal-residing B-1 cell by enzyme-linked immunospot (ELISPOT) assay. Taken together, these studies demonstrate the important role of natural Ab and complement in the clearance of pathogenic substances from the circulation.

Increased susceptibility to endotoxin shock in complement C3- and C4-deficient mice is corrected by C1 inhibitor replacement.

Endotoxin shock is a life-threatening syndrome associated with a Gram-negative infection and mediated by a systemic inflammatory response. As a major effector of inflammation, the complement system has been implicated in both the pathogenesis and the protection from endotoxin shock. To clarify the role of complement in endotoxin shock, we have used mice totally deficient in either complement component C3 or C4. We found that both the C3- and C4-deficient mice were significantly more sensitive to endotoxin than wild-type controls. The endotoxin-challenged complement-deficient mice failed to clear endotoxin efficiently from the circulation and this led to excess consumption of C1 inhibitor protein (C1 INH), a major regulator of both complement and the contact system of blood coagulation. Replacement of C1 INH rescued the endotoxin-challenged complement-deficient mice from shock and death. These findings suggest a novel therapy for treatment of endotoxemia with C1 INH protein.

Variable expression of WASP in B cell lines of Wiskott-Aldrich syndrome patients.

The Wiskott-Aldrich syndrome (WAS) arises from defects of the X-chromosome gene WASP. Severe platelet defects, thrombocytopenia with small platelets, are a hallmark of the disease, but clinical immunodeficiency based in lymphocyte dysfunction varies from negligible to life threatening among WAS patients. To address the connection between WASP mutations and clinical outcomes, we generated and characterized a panel of patient B cell lines. Three cell lines from patients with exon 2 missense mutations and mild immune dysfunction were found to express substantial levels of WASP mRNA and protein. On the other hand, 8 of 10 cell lines from patients with moderate or severe immune dysfunction lack detectable WASP protein. The findings suggest that the clinical variability of the WAS can partially be explained by the level of WASP protein in the patient's cells.

Molecular defects in hereditary angioneurotic edema.

Thirty-eight previously unreported, unrelated patients with hereditary angioneurotic edema were studied, and each was found to have a single mutation in the C1 inhibitor gene. On the basis of serine protease inhibitor crystal structure, these and published mutations affect critical domains in the reactive center loop, alpha-helices A, B, C, E, and F, and beta-sheets A and C. Almost all mutations, other than in the reactive center loop, occur at residues that are highly conserved among serine protease inhibitors, and the others are likely to interfere with molecular movement. These mutations begin to identify residues critical for molecular function of the C1 inhibitor molecule.