Hypomorphic Mutations in the BCR Signalosome Lead to Selective Immunoglobulin M Deficiency and Impaired B-cell Homeostasis

B cell activation via the B cell receptor (BCR) signalosome involves participation of signaling molecules such as BTK and BLNK. Genetic defects in these molecules are known to impair B cell differentiation and subsequently lead to agammaglobulinemia. Here we identified novel mutations in BTK and BLNK in two unrelated patients that perturb the intrinsic B-cell receptor signaling pathway and lead to selective IgM deficiency, whereas production of other immunoglobulin isotypes and IgG antibody response remain intact. Currently it is unknown how BCR signaling strength affects mature B cell development in humans. Both patients show reduced levels of BCR signalosome phosphorylation as well as impaired BCR-dependent Ca2+ influx, which was accompanied by a marked decrease in IgD+IgM+CD27+ MZ-like B-cells. We further describe reduced expression of essential B cell differentiation factors such as BAFF-R and T-Bet in the patients' B-cells, which might contribute to the observed deficiency of MZ-like B cells. MZ-like B cells are known to produce natural IgM antibodies that play an essential role in immune homeostasis. By using surface plasmon resonance (SPR) technology and a synthetic blood group A trisaccharide as antigen we were able to show that both patients lack the presence of anti-blood group A IgM considered to be prototypical natural antibodies whereas IgG levels were normal. Antibody binding dynamics and binding affinity of anti-blood group A IgG were comparable between patients and healthy controls. These results indicate that human IgM deficiency can be associated with signaling defects in the BCR signalosome, defective production of natural IgM antibodies in the blood group A/B/0 system and abnormalities in B cell development

Breathing Current Domains in Globally Coupled Electrochemical Systems: A Comparison with a Semiconductor Model

Spatio-temporal bifurcations and complex dynamics in globally coupled intrinsically bistable electrochemical systems with an S-shaped current-voltage characteristic under galvanostatic control are studied theoretically on a one-dimensional domain. The results are compared with the dynamics and the bifurcation scenarios occurring in a closely related model which describes pattern formation in semiconductors. Under galvanostatic control both systems are unstable with respect to the formation of stationary large amplitude current domains. The current domains as well as the homogeneous steady state exhibit oscillatory instabilities for slow dynamics of the potential drop across the double layer, or across the semiconductor device, respectively. The interplay of the different instabilities leads to complex spatio-temporal behavior. We find breathing current domains and chaotic spatio-temporal dynamics in the electrochemical system. Comparing these findings with the results obtained earlier for the semiconductor system, we outline bifurcation scenarios leading to complex dynamics in globally coupled bistable systems with subcritical spatial bifurcations.Comment: 13 pages, 11 figures, 70 references, RevTex4 accepted by PRE http://pre.aps.or

Prevalence and clinical challenges among adults with primary immunodeficiency and recombination-activating gene deficiency.

Letter to the Edito

Leaky RAG Deficiency in Adult Patients with Impaired Antibody Production against Bacterial Polysaccharide Antigens.

Loss of function mutations in the recombination activating genes RAG1 and RAG2 have been reported to cause a T-B-NK+ type of severe combined immunodeficiency. In addition identification of hypomorphic mutations in RAG1 and RAG2 has led to an expansion of the spectrum of disease to include Omenn syndrome, early onset autoimmunity, granuloma, chronic cytomegalovirus- or EBV-infection with expansion of gamma/delta T-cells, idiophatic CD4 lymphopenia and a phenotype resembling common variable immunodeficiency. Herein we describe a novel presentation of leaky RAG1 and RAG2 deficiency in two unrelated adult patients with impaired antibody production against bacterial polysaccharide antigens. Clinical manifestation included recurrent pneumonia, sinusitis, otitis media and in one patient recurrent cutaneous vasculitis. Both patients harbored a combination of a null mutation on one allele with a novel hypomorphic RAG1/2 mutation on the other allele. One of these novel mutations affected the start codon of RAG1 and resulted in an aberrant gene and protein expression. The second novel RAG2 mutation leads to a truncated RAG2 protein, lacking the C-terminus with intact core RAG2 and reduced VDJ recombination capacity as previously described in a mouse model. Both patients presented with severely decreased numbers of naïve CD4+ T cells and defective T independent IgG responses to bacterial polysaccharide antigens, while T cell-dependent IgG antibody formation e.g. after tetanus or TBEV vaccination was intact. In conclusion, hypomorphic mutations in genes responsible for SCID should be considered in adults with predominantly antibody deficiency

Immunological characteristics of patients with hypomorphic RAG deficiency and impaired antibody production against bacterial polysaccharide antigens.

<p>Patient A…circles; patient B…triangles 22 (A) Impaired antibody production against bacterial polysaccharide antigens in RAG-deficient patients. Box-plots represent pn23-antibodies in 41 healthy individuals (B) Numbers of CD4⁺CD45RA⁺ (naïve CD4) and CD8⁺CD45RA⁺CD62L⁺ (naïve CD8) T cells given as percentage of total CD8- or CD4-positive T cells. Box-plots depict 50 healthy individuals (C) Kinetic of the total count of CD4⁺ T cells and naïve CD4⁺CD45RA⁺ T cell depicted as average of both patients (D) Representative example of the distribution of TCR Vbeta genes 16, 17, 18, 22 (E) Numbers of switched memory B cells given as percentage of total CD19 B cells. Box-plots depict 50 healthy individuals (F) Numbers of CD21^low B cells given as percentage of total CD19 B cells. Box-plots depict 50 healthy individuals (median,+; box, IQR; whiskers, q5-q95).</p

RAG1/2 Mutation analysis of genomic DNA from peripheral blood.

<p>(A) Patient A is compound heterozygous in RAG1, c.1 A>G, p.M1V; c.2322 G>A, p.R737H. Allele-specific PCR was used to characterize RAG1 M1V and R737H alleles. (B) Patient B is compound heterozygous in RAG2, c1347-8delCT, pSer381Terfs*1; c488G>A, pGlu95R. Mutation analysis of the son of patient B identified the compound heterozygosity of the RAG2 missense mutations. (C) Schematic depiction of RAG1 (D) Schematic depiction of RAG2. Mutations are indicated by rectangles.</p

In vitro immunoglobulin production and ³H-Thymidin incorporation of PBMCs and lymphoblastoid cells.

<p>Unstimulated peripheral blood mononuclear cells and EBV-transformed lymphoblastoid cells were incubated for 8 days and the supernatant IgM/G concentration was determined by ELISA. Additionally the ³H-thymidin incorporation was determined. Results are expressed as mean and standard deviation (control unstimulated IgM/G: n = 9; control EBV-transformed IgM/G: n = 3; patient EBV-transformed IgM/G: n = 1 (triplicate); control unstimulated ³H-thymidin incorporation: n = 9; control EBV-transformed ³H-thymidin incorporation: n = 1 (triplicate); patient EBV-transformed ³H-thymidin incorporation: n = 1 (triplicate)).</p><p>In vitro immunoglobulin production and ³H-Thymidin incorporation of PBMCs and lymphoblastoid cells.</p