Mutational analysis of human BAFF receptor TNFRSF13C (BAFF-R) in patients with common variable immunodeficiency.
ABSTRACT BAFF receptor (BAFF-R/BR3/TNFRSF13C) is a recently identified molecule that specifically binds BLyS, a protein belonging to the tumor necrosis factor (TNF) family, and is involved in survival and maturation of B cells. Recent studies have demonstrated that mice defective in BAFF-R gene exhibit an altered profile of the B cell pool, a phenotype observed in BLyS knockout mice as well. These features suggest that mutations in this gene may result in humoral immunodeficiency. To test this hypothesis, we sequenced the BAFF-R gene in 48 patients with common variable immunodeficiency (CVID) along with 57 healthy controls. We have identified three novel variants present at the heterozygous state leading to amino acid substitutions, and have also confirmed the existence of a previously reported intronic variant. The hereby described novel variants were also present in healthy controls and in the healthy patients' parents. These variants do not affect the expression of BAFF-R neither at the mRNA nor at the protein level, suggesting that these variants represent novel polymorphic variants of the BAFF-R gene.
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ABSTRACT: The tumor necrosis factor family members BAFF and APRIL induce Ig isotype switching in human B cells. We analyzed the ability of BAFF and APRIL to induce isotype switching in murine B cells to IgG1, IgA, and IgE. APRIL and BAFF each engage two receptors, transmembrane activator and calcium-modulator and cytophilin ligand interactor (TACI) and B cell maturation antigen (BCMA), on B cells. In addition, BAFF engages a third receptor on B cells, BAFF-R. To determine the role of these receptors in isotype switching, we examined B cells from mice deficient in TACI, BCMA, and BAFF-R. The results obtained indicate that both TACI and BAFF-R are able to transduce signals that result in isotype switching.Journal of Experimental Medicine 02/2005; 201(1):35-9. · 13.21 Impact Factor
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ABSTRACT: The molecular basis of common variable immunodeficiency (CVID) is unknown. To assess humoral immunity in CVID, we selected 24 patients with early or late onset of disease. X-linked agammaglobulinemia (XLA), X-linked hyper-IgM syndrome (XHIM), and non-XHIM were excluded based on clinical phenotype, assessment of the immune response, presence of Bruton's tyrosine kinase (Btk) in monocytes or platelets, and normal expression of CD40 ligand by activated T cells. The number of circulating B cells was within the normal range or reduced. IgD(-) CD27(+) memory B cells were markedly reduced or absent in all 24 patients and IgD(+) CD27(+) B cells were diminished in 8 patients. Circulating B cells from all 6 patients examined, including CVID patients with IgD(+) CD27(+) cells, failed to undergo somatic hypermutation in immunoglobulin-variable (V)-region genes, similar to cord blood B cells. B cells from CVID patients produced IgM and IgG, but not IgA upon the engagement of Ig receptor and CD40 in the presence of IL-2 and IL-10. B cells from all but 5 patients secreted IgE when stimulated by CD40 crosslinking in the presence of IL-4. The observation of defective memory B cells with abnormal cell marker expression and function demonstrates that naive CVID B cells including those expressing IgD(+) CD27(+), in analogy to cord blood and hyper-IgM syndrome B cells, may be responsible for their failure to differentiate into plasma cells and to produce high-affinity antibodies of different isotypes.Clinical Immunology 05/2002; 103(1):34-42. · 3.77 Impact Factor
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ABSTRACT: Herein we demonstrate that B cell-activating factor of the TNF family (BAFF), a B cell survival factor, also regulates CD21/35 and CD23 expression. BAFF blockade in wild-type mice down-modulates CD21/35 and CD23 on B cells while survival remains intact, and BAFF exposure causes elevated CD21/35 and CD23 expression. Similar down-modulation is observed in bcl-2-transgenic mice treated with a BAFF inhibitor. This is the first evidence that BAFF has a function independent of B cell survival. Reports using CD21/35 and CD23 expression to assess splenic B cell subsets in BAFF-null mice concluded a lack of B cells beyond the immature stage. Since CD21/35 and CD23 are inadequate for delineating B cell subpopulations in BAFF-null mice, we used expression of BAFF-R and several B cell markers to identify more mature splenic B cells in these mice. These data broaden our understanding of BAFF function and correct the view that BAFF-null mice lack mature B cells.The Journal of Immunology 02/2004; 172(2):762-6. · 5.52 Impact Factor