Baerbel Keller

Circulating CD21low B cells in common variable immunodeficiency resemble tissue homing, innate-like B cells.

The homeostasis of circulating B cell subsets in the peripheral blood of healthy adults is well regulated, but in disease it can be severely disturbed. Thus, a subgroup of patients with common variable immunodeficiency (CVID) presents with an extraordinary expansion of an unusual B cell population characterized by the low expression of CD21. CD21low B cells are polyclonal, unmutated IgM+IgD+ B cells but carry a highly distinct gene expression profile which differs from conventional naïve B cells. Interestingly, while clearly not representing a memory population, they do share several features with the recently defined memory-like tissue, Fc receptor-like 4 positive B cell population in the tonsils of healthy donors. CD21low B cells show signs of previous activation and proliferation in vivo, while exhibiting defective calcium signaling and poor proliferation in response to B cell receptor stimulation. CD21low B cells express decreased amounts of homeostatic but increased levels of inflammatory chemokine receptors. This might explain their preferential homing to peripheral tissues like the bronchoalveolar space of CVID or the synovium of rheumatoid arthritis patients. Therefore, as a result of the close resemblance to the gene expression profile, phenotype, function and preferential tissue homing of murine B1 B cells, we suggest that CD21low B cells represent a human innate-like B cell population.

Deficiency of caspase recruitment domain family, member 11 (CARD11), causes profound combined immunodeficiency in human subjects

BACKGROUND Profound combined immunodeficiency can present with normal numbers of T and B cells, and therefore the functional defect of the cellular and humoral immune response is often not recognized until the first severe clinical manifestation. Here we report a patient of consanguineous descent presenting at 13 months of age with hypogammaglobulinemia, Pneumocystis jirovecii pneumonia, and a suggestive family history. OBJECTIVE We sought to identify the genetic alteration in a patient with combined immunodeficiency and characterize human caspase recruitment domain family, member 11 (CARD11), deficiency. METHODS Molecular, immunologic, and functional assays were performed. RESULTS The immunologic characterization revealed only subtle changes in the T-cell and natural killer cell compartment, whereas B-cell differentiation, although normal in number, was distinctively blocked at the transitional stage. Genetic evaluation revealed a homozygous deletion of exon 21 in CARD11 as the underlying defect. This deletion abrogated protein expression and activation of the canonical nuclear factor κB (NF-κB) pathway in lymphocytes after antigen receptor or phorbol 12-myristate 13-acetate stimulation, whereas CD40 signaling in B cells was preserved. The abrogated activation of the canonical NF-κB pathway was associated with severely impaired upregulation of inducible T-cell costimulator, OX40, cytokine production, proliferation of T cells, and B cell-activating factor receptor expression on B cells. CONCLUSION Thus in patients with CARD11 deficiency, the combination of impaired activation and especially upregulation of inducible T-cell costimulator on T cells, together with severely disturbed peripheral B-cell differentiation, apparently leads to a defective T-cell/B-cell cooperation and probably germinal center formation and clinically results in severe immunodeficiency. This report discloses the crucial and nonredundant role of canonical NF-κB activation and specifically CARD11 in the antigen-specific immune response in human subjects.

Haploinsufficiency of the NF-κB1 Subunit p50 in Common Variable Immunodeficiency

Common variable immunodeficiency (CVID), characterized by recurrent infections, is the most prevalent symptomatic antibody deficiency. In ∼90% of CVID-affected individuals, no genetic cause of the disease has been identified. In a Dutch-Australian CVID-affected family, we identified a NFKB1 heterozygous splice-donor-site mutation (c.730+4A>G), causing in-frame skipping of exon 8. NFKB1 encodes the transcription-factor precursor p105, which is processed to p50 (canonical NF-κB pathway). The altered protein bearing an internal deletion (p.Asp191_Lys244delinsGlu; p105ΔEx8) is degraded, but is not processed to p50ΔEx8. Altered NF-κB1 proteins were also undetectable in a German CVID-affected family with a heterozygous in-frame exon 9 skipping mutation (c.835+2T>G) and in a CVID-affected family from New Zealand with a heterozygous frameshift mutation (c.465dupA) in exon 7. Given that residual p105 and p50—translated from the non-mutated alleles—were normal, and altered p50 proteins were absent, we conclude that the CVID phenotype in these families is caused by NF-κB1 p50 haploinsufficiency.

B Cell Receptor-Mediated Calcium Signaling Is Impaired in B Lymphocytes of Type Ia Patients with Common Variable Immunodeficiency

Several lines of evidence have demonstrated B cell intrinsic activation defects in patients with common variable immunodeficiency (CVID). The rapid increase of intracellular free calcium concentrations after engagement of the BCR represents one crucial element in this activation process. The analysis of 53 patients with CVID for BCR-induced calcium flux identified a subgroup of patients with significantly reduced Ca2+ signals in primary B cells. This subgroup strongly corresponded to the class Ia of the Freiburg classification. Comparison at the level of defined B cell subpopulations revealed reduced Ca2+ signals in all mature B cell populations of patients with CVID class Ia when compared with healthy individuals and other groups of patients with CVID but not in circulating transitional B cells. BCR-induced Ca2+ responses were the lowest in CD21low B cells in patients as well as healthy donors, indicating an additional cell-specific mechanism inhibiting the Ca2+ flux. Although proximal BCR signaling events are unperturbed in patients’ B cells, including normal phospholipase Cγ2 phosphorylation and Ca2+ release from intracellular stores, Ca2+ influx from the extracellular space is significantly impaired. CD22, a negative regulator of calcium signals in B cells, is highly expressed on CD21low B cells from patients with CVID Ia and might be involved in the attenuated Ca2+ response of this B cell subpopulation. These data from patients with CVID suggest that a defect leading to impaired BCR-induced calcium signaling is associated with the expansion of CD21low B cells, hypogammaglobulinemia, autoimmune dysregulation, and lymphadenopathy.

CD21low B cells in common variable immunodeficiency do not show defects in receptor editing, but resemble tissue-like memory B cells.

To the editor: We read with great interest the article by Isnardi et al[1][1] wherein the authors showed very similar phenotypic and genotypic features of CD21−/lo B cells as previously reported.[2][2] In view of the polyreactivity, increased autoreactivity, and strongly reduced calcium response

Telomere-dependent replicative senescence of B and T cells from patients with type 1a common variable immunodeficiency

A subset of patients with common variable immunodeficiency (CVID), group 1a of the Freiburg classification, is characterized by increased B cells expressing low levels of CD21 (CD21low), lymphoproliferation and autoimmunity. The CD21low B cells have been shown to be profoundly anergic, and defects of BCR‐mediated calcium signaling and of T cells have been described in CVID 1a. We found that also the classical naïve B cells from CVID 1a patients, but not from CVID non‐1a patients, proliferated poorly. The B cells of CVID 1a patients had a reduced capacity to divide reminiscent of the proliferative arrest associated with replicative senescence. Thus, we investigated whether lymphocyte dysfunction in CVID 1a was related to telomere‐dependent replicative senescence, and found that both the B and the T cells from CVID 1a patients had significantly shorter telomeres compared with B and T cells from CVID non‐1a patients. Telomere lengths in B and T cells were significantly correlated, indicating that the rate of telomere attrition in lymphocytes is an individual characteristic of CVID patients. Our findings suggest that telomere‐dependent replicative senescence contributes to the immune dysfunction of CVID 1a patients, and may provide an important clue for a better understanding of the pathogenesis of CVID.

Extending the clinical and immunological phenotype of human interleukin-21 receptor deficiency

Combined immune deficiencies (CID) are defined by severely impaired adaptive immunity leading to increased susceptibility to opportunistic infections, immune dysregulation and malignancies. CID of moderate severity may not lead to death in infancy but still carry a high burden of morbidity and

Preserved effector functions of human ORAI1- and STIM1-deficient neutrophils

To the Editor: The endoplasmic reticulum (ER) Ca sensor stromal interaction molecule 1 (STIM1) and the plasma membrane protein ORAI1, which forms the pore of the Ca release-activated Ca (CRAC) channel, are the core components of storeoperated calcium entry (SOCE). SOCE is an essential pathway of lymphocyte activation, where engagement of immunostimulatory receptors triggers Ca release from the ER through inositol 1,4,5 trisphosphate formation. STIM1 and STIM2 subsequently induce opening of CRAC channels, which are composed of ORAI proteins (ORAI1-ORAI3). Inherited mutations in ORAI1 or STIM1 genes, which abolish SOCE, cause a combined immunodeficiency syndrome accompanied by various nonhematopoietic manifestations. Whereas the T-cell defect is well established as a key mechanism mediating the immunophenotype of SOCE-deficient patients, the contribution of dysfunctional innate immunity to the broad susceptibility to infections in affected patients is unclear. In particular, data on human polymorphonuclear neutrophils (PMNs) derived from SOCE-deficient patients are lacking. Studies in mice and in human neutrophil-like cell lines suggest a substantial role for SOCE in antimicrobial PMN functions, including phagocytosis, degranulation, and superoxide (reactive oxygen species [ROS]) production. In contrast, other reports implicate non-SOCE mechanisms, such as receptor-operated Ca entry, which is directly mediated by cell-surface receptors and independent of ER stores, as important mediators of PMN activation. A more detailed understanding of SOCE in PMN function is of obvious importance both for understanding the susceptibility to the broad spectrum of microorganisms in patients with SOCE deficiency and because SOCE inhibition in PMNs has been proposed as an anti-inflammatory treatment strategy. We analyzed Ca signals and effector functions in PMNs from 2 patients with loss-of-function mutations in ORAI1 and STIM1 genes. Surprisingly, and in contrast to T cells, Ca influx was only mildly reduced in ORAI1and STIM1-deficient PMNs, and detailed studies did not reveal overt defects in PMN function. Accordingly, in contrast to mice, STIM1 and ORAI1 do not appear to be critical for various effector functions of human PMNs. Methodically, human PMNs were isolated from EDTA blood by means of Biocoll (Biochrom, Berlin, Germany) density gradient centrifugation. Intracellular Ca mobilization was measured by using flow cytometry after labeling with Indo-1 (Invitrogen, Grand Island, NY) and stimulation with formylated methionyl-leucyl-phenylalanine (fMLP; 100 mmol/L), heatfixed streptococci (10/mL), ionomycin (2 mmol/L), or thapsigargin (1 mmol/L). The functional PMN assays (adhesion, chemotaxis, IL-8 production, and ROS formation) were described earlier. Phagocytosis of fluorophore-stained and heat-fixed streptococci was measured by means of flow cytometry after PMN fixation with paraformaldehyde and trypan blue quenching. More details are provided in the Methods section and Table E1 in this article’s Online Repository at www.jacionline.org.

Generalized verrucosis and HPV-3 susceptibility associated with CD4 T-cell lymphopenia caused by inherited human interleukin-7 deficiency

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Enteroviral Infection in a Patient with BLNK Adaptor Protein Deficiency

B-cell linker (BLNK) protein is a non-redundant adaptor molecule in the signaling pathway activated by (pre) B-cell antigen receptor signals. We present two siblings with a homozygous deleterious frameshift mutation in BLNK, resulting in a block of B cell development in the bone marrow at the preB1 to preB2 stage, absence of circulating B cells and agammaglobulinemia. This is the first description of an enteroviral infection associated arthritis and dermatitis in a patient with BLNK deficiency.