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. 2001 Jan 30;98(3):1166-70.
doi: 10.1073/pnas.98.3.1166.

VSports注册入口 - CD40-CD40L independent Ig gene hypermutation suggests a second B cell diversification pathway in humans

S Weller  1 , A Faili, C Garcia, M C Braun, F Le Deist F, G de Saint Basile G, O Hermine, A Fischer, C A Reynaud, J C Weill
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CD40-CD40L independent Ig gene hypermutation suggests a second B cell diversification pathway in humans

S Weller et al. Proc Natl Acad Sci U S A. .

"V体育官网入口" Abstract

Somatically mutated IgM(+)-only and IgM(+)IgD(+)CD27(+) B lymphocytes comprise approximately 25% of the human peripheral B cell pool. These cells phenotypically resemble class-switched B cells and have therefore been classified as postgerminal center memory B cells. X-linked hyper IgM patients have a genetic defect characterized by a mutation of the CD40L gene. These patients, who do not express a functional CD40 ligand, cannot switch Ig isotypes and do not form germinal centers and memory B cells. We report here that an IgM(+)IgD(+)CD27(+) B cell subset with somatically mutated Ig receptors is generated in these patients, implying that these cells expand and diversify their Ig receptors in the absence of classical cognate T-B collaboration. The presence of this sole subset in the absence of IgM(+)-only and switched CD27(+) memory B cells suggests that it belongs to a separate diversification pathway. VSports手机版.

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Figures

Figure 1
Figure 1
Location of CD40L mutations in XHIM patients. The schematic representation of the cDNA sequence and of the domains of the CD40L molecule is according to Seyama et al. (17). IC, intracellular tail; TM, transmembrane domain; ECU, extracellular unique region; TNFH, tumor necrosis factor-homology domain. For each exon and domain, the starting nucleotide or amino acid residue number is indicated. Nonsense mutations are shown above the scheme, insertions (ins) and deletions (del) below.
Figure 2
Figure 2
Fluorescence analysis and sorting of IgD+CD27+ peripheral blood B cells of XHIM patients and a control adult donor. (A) Anti-IgD/anti-CD27 two-color staining of CD19+ B cells enriched by magnetic cell sorting (MACS) was performed as described in Materials and Methods. The gates selected for sorting of the IgD+CD27+ B cell population are indicated. The IgD−CD27+ population present in XHIM patients corresponds to a residual T cell contamination (see B and Materials and Methods). The sorted fractions were used for sequence analysis of rearranged VH3–23 gene segments. (B) Anti-IgD/anti-CD27/anti-CD19 three-color staining performed on peripheral blood mononuclear cells confirmed the absence of IgD−CD27+ memory B cells in XHIM patients. Three-color analysis shows CD27 and IgD expression on CD19+-gated cells. The data are representative of all XHIM patients studied.
Figure 3
Figure 3
Distribution of mutations in rearranged VH3–23 gene segments from control donors and XHIM patients. Each histogram represents the percentage of VH3–23 sequences displaying the number of mutations in a given range. Because of his remarkable mutation profile, patient C.Q. was represented separately from the other XHIM patients. (Patient Z.A., for whom mutation frequency was close to background level, was not included in this analysis.) The number of V sequences analyzed in each group is: control children, n = 33; control adults, n = 37; XHIM patients, n = 125; patient C.Q., n = 28.
Figure 4
Figure 4
Proposed scheme of human B cell development leading to Ig gene hypermutation. Pathway I corresponds to T-dependent responses occurring in GCs. Pathway II could correspond to T-independent responses, which may include nonconventional help from natural killer or T cells. The splenic marginal zone (MZ) or equivalent sites in Peyer's patches or lymph nodes could be the site of B cell activation. Ig gene hypermutation takes place in both pathways.
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