Background Ataxia telangiectasia (AT) is a multisystem DNA-repair disorder caused by mutations in the ataxia telangiectasia mutated (ATM) gene. Patients with AT have reduced B- and T-cell numbers and ...a highly variable immunodeficiency. ATM is important for V(D)J recombination and immunoglobulin class-switch recombination (CSR); however, little is known about the mechanisms resulting in antibody deficiency severity. Objective We sought to examine the immunologic mechanisms responsible for antibody deficiency heterogeneity in patients with AT. Methods In this study we included patients with classical AT plus early-onset hypogammaglobulinemia (n = 3), classical AT (n = 8), and variant AT (late onset, n = 4). We studied peripheral B- and T-cell subsets, B-cell subset replication history, somatic hypermutation frequencies, CSR patterns, B-cell repertoire, and ATM kinase activity. Results Patients with classical AT lacked ATM kinase activity, whereas patients with variant AT showed residual function. Most patients had disturbed naive B-cell and T-cell homeostasis, as evidenced by low cell numbers, increased proliferation, a large proportion CD21low CD38low anergic B cells, and decreased antigen receptor repertoire diversity. Impaired formation of T cell–dependent memory B cells was predominantly found in patients with AT plus hypogammaglobulinemia. These patients had extremely low naive CD4+ T-cell counts, which were more severely reduced compared with those seen in patients with classical AT without hypogammaglobulinemia. Finally, AT deficiency resulted in defective CSR to distal constant regions that might reflect an impaired ability of B cells to undergo multiple germinal center reactions. Conclusion The severity of the antibody deficiency in patients with AT correlates with disturbances in B- and T-cell homeostasis resulting in reduced immune repertoire diversity, which consequently affects the chance of successful antigen-dependent cognate B-T interaction.
Background The prevalence of IgE-mediated diseases has been increasing worldwide, yet IgE-expressing B cells are poorly characterized, mainly because of their scarcity and low membrane IgE levels. ...Objective We sought to study the immunobiology of human IgE-expressing B cells in healthy subjects and patients with allergic disease. Methods We used a stepwise approach for flow cytometric detection and purification of human IgE-expressing B cells in control subjects, CD40 ligand–deficient patients, and patients with atopic dermatitis. Molecular analysis of replication histories, somatic hypermutation (SHM), and immunoglobulin class-switching was performed. Results Using multicolor flow cytometry, we reliably detected IgE-expressing plasma cells and 2 IgE-expressing memory B-cell subsets. These IgE-expressing cells showed molecular and phenotypic signs of antigen responses. The replication history and SHM levels of IgE+ plasma cells and CD27+ IgE+ memory B cells fitted with a germinal center (GC)–dependent pathway, often through an IgG intermediate, as evidenced from Sγ remnants in Sμ-Sε switch regions. CD27− IgE+ cells showed limited proliferation and SHM and were present in CD40 ligand–deficient patients, indicating a GC-independent origin. Patients with atopic dermatitis had normal numbers of blood IgE+ plasma cells and CD27+ IgE+ memory B cells but increased numbers of CD27− IgE+ memory B cells with high SHM loads compared with those seen in healthy control subjects and patients with psoriasis. Conclusions We delineated GC-dependent and GC-independent IgE+ B-cell responses in healthy subjects and indicated involvement of the GC-independent pathway in a human IgE-mediated disease. These findings provide new insights into the pathogenesis of IgE-mediated diseases and might contribute to accurate monitoring of IgE+ B cells in patients with severe disease undergoing anti-IgE treatment.
Background Individuals with genetic defects in CD40 ligand (CD40L) or B-cell antigen receptor coreceptor molecules CD19 and CD81 suffer from an antibody deficiency. Still, these patients carry low ...levels of memory B cells and serum antibodies. Objective We sought to assess why the remaining memory B cells and antibodies in the blood of these patients do not provide functional immunity. Methods We included CD19-deficient patients (n = 8), CD40L-deficient patients (n = 8), and healthy controls (n = 50) to perform detailed flow cytometry on blood B cells, molecular analysis of IgA and IgG transcripts, as well as functional analysis of B-cell activation. Results CD19-deficient and CD40L-deficient patients carried reduced numbers of all memory B-cell subsets except CD27− IgA+ B cells. Their immunoglobulin heavy chain class-switched transcripts contained less somatic mutations and reduced usage of IgM-distal IgG2 and IgA2 subclasses. The selection strength of mutations for antigen binding was significantly lower than in controls, whereas selection to maintain superantigen binding was normal. Furthermore, the patients showed impaired selection against inherently autoreactive properties of their immunoglobulins. Somatic hypermutation analysis revealed decreased activation-induced cytidine deaminase and uracil-DNA glycosylase 2 activity in CD40L deficiency and increased uracil-DNA glycosylase 2 but decreased mismatch repair in CD19 deficiency. B-cell activation studies revealed that this was at least in part due to transcriptional regulation of DNA repair genes. Conclusions This study on CD19 and CD40L deficiencies illustrates that both the B-cell antigen receptor and CD40 signaling pathways are required for the selection of immunoglobulin reactivity. Still, they differentially mediate DNA repair pathways during somatic hypermutation, thereby together shaping the human in vivo antigen-experienced B-cell repertoire.
Background V(D)J recombination takes place during lymphocyte development to generate a large repertoire of T- and B-cell receptors. Mutations in recombination-activating gene 1 (RAG1) and RAG2 result ...in loss or reduction of V(D)J recombination. It is known that different mutations in RAG genes vary in residual recombinase activity and give rise to a broad spectrum of clinical phenotypes. Objective We sought to study the immunologic mechanisms causing the clinical spectrum of RAG deficiency. Methods We included 22 patients with similar RAG1 mutations (c.519delT or c.368_369delAA) resulting in N-terminal truncated RAG1 protein with residual recombination activity but presenting with different clinical phenotypes. We studied precursor B-cell development, immunoglobulin and T-cell receptor repertoire formation, receptor editing, and B- and T-cell numbers. Results Clinically, patients were divided into 3 main categories: T− B− severe combined immunodeficiency, Omenn syndrome, and combined immunodeficiency. All patients showed a block in the precursor B-cell development, low B- and T-cell numbers, normal immunoglobulin gene use, limited B- and T-cell repertoires, and slightly impaired receptor editing. Conclusion This study demonstrates that similar RAG mutations can result in similar immunobiological effects but different clinical phenotypes, indicating that the level of residual recombinase activity is not the only determinant for clinical outcome. We postulate a model in which the type and moment of antigenic pressure affect the clinical phenotypes of these patients.
...in mice reconstituted with low Rag1 expression, a block in development can be seen at the immature single positive to DP transition. ...the level of RAG1 expression in transduced stem cells and ...after transplantation and reconstitution in lymphocytes is a crucial determinant of outcome.
Defective B-cell memory in patients with Down syndrome Verstegen, Ruud H.J., MD; Driessen, Gertjan J., MD; Bartol, Sophinus J.W., BSc ...
Journal of allergy and clinical immunology,
12/2014, Letnik:
134, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Background Patients with Down syndrome carry immunologic defects, as evidenced by the increased risks for autoimmune diseases, hematologic malignancies, and respiratory tract infections. Moreover, ...the low numbers of circulating B cells suggest impaired humoral immunity. Objective We sought to study how immunodeficiency in patients with Down syndrome results from immunologic defects in the B-cell compartment. Methods We studied blood B-cell subset composition, replication history, somatic hypermutation status, and class-switch recombination in 17 children with Down syndrome. Germinal centers and plasma cells were studied in tonsils from 4 additional children with Down syndrome. Results Blood transitional B-cell numbers were normal, but naive mature and memory B-cell numbers were reduced despite slightly increased serum B cell–activating factor levels. Germinal centers and plasma cells in tonsils appeared normal, as were serum immunoglobulin levels. CD27+ IgD+ IgM+ “natural effector” B cells showed reduced proliferation and somatic hypermutation levels, whereas these were normal in CD27+ IgD− memory B cells. Furthermore, IgM+ and IgA+ , but not IgG+ , memory B cells showed impaired molecular signs for antigen selection. The B-cell pattern was highly similar to that of patients with common variable immunodeficiency and a defect in B-cell activation and proliferation. Conclusion Children with Down syndrome seem capable of normal germinal center and plasma cell formation. Still, blood memory B-cell numbers were reduced and showed impaired molecular maturation of IgA and IgM, which are important for mucosal immunity. The observed molecular defects in circulating IgA and IgM B-cell memory could reflect impaired local responses, which underlie the increased susceptibility to respiratory tract infections of patients with Down syndrome.
Background Severe combined immunodeficiency (SCID) represents congenital disorders characterized by a deficiency of T cells caused by arrested development in the thymus. Yet the nature of these ...developmental blocks has remained elusive because of the difficulty of taking thymic biopsy specimens from affected children. Objective We sought to identify the stages of arrest in human T-cell development caused by various major types of SCID. Methods We performed transplantation of SCID CD34+ bone marrow stem/progenitor cells into an optimized NSG xenograft mouse model, followed by detailed phenotypic and molecular characterization using flow cytometry, immunoglobulin and T-cell receptor spectratyping, and deep sequencing of immunoglobulin heavy chain (IGH) and T-cell receptor δ (TRD) loci. Results Arrests in T-cell development caused by mutations in IL-7 receptor α (IL7RA) and IL-2 receptor γ (IL2RG) were observed at the most immature thymocytes much earlier than expected based on gene expression profiling of human thymocyte subsets and studies with corresponding mouse mutants. T-cell receptor rearrangements were functionally required at the CD4− CD8− CD7+ CD5+ stage given the developmental block and extent of rearrangements in mice transplanted with Artemis-SCID cells. The xenograft model used is not informative for adenosine deaminase–SCID, whereas hypomorphic mutations lead to less severe arrests in development. Conclusion Transplanting CD34+ stem cells from patients with SCID into a xenograft mouse model provides previously unattainable insight into human T-cell development and functionally identifies the arrest in thymic development caused by several SCID mutations.
Background Numbers of blood leukocyte subsets are highly dynamic in childhood and differ greatly between subjects. Interindividual variation is only partly accounted for by genetic factors. Objective ...We sought to determine which nongenetic factors affect the dynamics of innate leukocytes and naive and memory lymphocyte subsets. Methods We performed 6-color flow cytometry and linear mixed-effects modeling to define the dynamics of 62 leukocyte subsets from birth to 6 years of age in 1182 children, with 1 to 5 measurements per subject. Subsequently, we defined the effect of prenatal maternal lifestyle-related or immune-mediated determinants, birth characteristics, and bacterial/viral exposure–related determinants on leukocyte subset dynamics. Results Functionally similar leukocyte populations were grouped by using unbiased hierarchical clustering of patterns of age-related leukocyte dynamics. Innate leukocyte numbers were high at birth and predominantly affected by maternal low education level. Naive lymphocyte counts peaked around 1 year, whereas most memory lymphocyte subsets more gradually increased during the first 4 years of life. Dynamics of CD4+ T cells were predominantly associated with sex, birth characteristics, and persistent infections with cytomegalovirus (CMV) or EBV. CD8+ T cells were predominantly associated with CMV and EBV infections, and T-cell receptor γδ+ T cells were predominantly associated with premature rupture of membranes and CMV infection. B-cell subsets were predominantly associated with sex, breast-feeding, and Helicobacter pylori carriership. Conclusions Our study identifies specific dynamic patterns of leukocyte subset numbers, as well as nongenetic determinants that affect these patterns, thereby providing new insights into the shaping of the childhood immune system.
Intraocular lymphoma (IOL) is a rare condition and frequently difficult to distinguish from uveitis or other uveitis-masquerading syndromes. The diagnosis is confirmed by cytologic examination of ...ocular fluid specimens and more recently by molecular-immunoglobulin heavy chain (IGH) translocation or cytokine analysis. However, some of these more recent methods have not been validated by follow-up studies.
Evaluation of a diagnostic test.
In a cohort of 51 consecutive patients with a clinical suspicion of IOL, vitreous analysis was performed via multicolor flowcytometric immunophenotyping.
Multicolor flowcytometric immunophenotyping was performed with CD45, CD3, CD19, CD20, anti-SmIgκ, and anti-SmIgλ antibodies. The presence of a clear B-cell population showing a disequilibrium of Igκ versus Igλ expression was used to confirm the diagnosis of non-Hodgkin lymphoma (NHL). Patients were followed for a minimum of 2 years (mean, 5.9 ± 2.0 years) to validate the accuracy of the method.
The presence or absence of IOL during follow-up.
In 14 of 51 patients, a clinical diagnosis of IOL was confirmed using flowcytometric analysis. Of these 14 patients, 11 had primary IOL and 3 had metastasized secondary lymphomas. In 3 of 51 patients who were diagnosed with (central nervous system) NHL during follow-up, the test failed to confirm the presence of a clonal B-cell population. In 18 of the 34 other patients, an infectious or well-defined immunologic disorder was established during follow-up. The remaining 16 patients, with a minimal follow-up of 2 years, were diagnosed with idiopathic uveitis.
Multicolor flowcytometric analysis had 82.4% sensitivity and 100% specificity in patients with suspected IOL. This is comparable to the reported vitreous interleukin (IL)-6/IL-10 testing sensitivity of 0.8 and sensitivity of 0.65 to 0.95 by immunoglobulin heavy chain (IGH) gene arrangement testing in clinical cohorts. Because flowcytometric tests are readily performed in hematologic laboratories, this can be regarded as a useful method for confirming the clinical diagnosis of IOL.
The author(s) have no proprietary or commercial interest in any materials discussed in this article.
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