Selective generation of functional somatically mutated IgM+CD27+, but not Ig isotype-switched, memory B cells in X-linked lymphoproliferative disease
Cindy S. Ma, … , Kim E. Nichols, Stuart G. Tangye
Cindy S. Ma, … , Kim E. Nichols, Stuart G. Tangye
Published February 1, 2006
Citation Information: J Clin Invest. 2006;116(2):322-333. https://doi.org/10.1172/JCI25720.
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Research Article Immunology

Selective generation of functional somatically mutated IgM+CD27+, but not Ig isotype-switched, memory B cells in X-linked lymphoproliferative disease

Abstract

Individuals with X-linked lymphoproliferative disease (XLP) display defects in B cell differentiation in vivo. Specifically, XLP patients do not generate a normal number of CD27+ memory B cells, and those few that are present are IgM+. Recent studies have suggested that IgM+CD27+ B cells are not true memory cells, but rather B cells that guard against T cell–independent pathogens. Here we show that human XLP IgM+CD27+ B cells resemble normal memory B cells both morphologically and phenotypically. Additionally, IgM+CD27+ B cells exhibited functional characteristics of normal memory B cells, including the ability to secrete more Ig than naive B cells in response to both T cell–dependent and –independent stimuli. Analysis of spleens from XLP patients revealed a paucity of germinal centers (GCs), and the rare GCs detected were poorly formed. Despite this, Ig variable region genes expressed by XLP IgM+CD27+ B cells had undergone somatic hypermutation to an extent comparable to that of normal memory B cells. These findings reveal a differential requirement for the generation of IgM+ and Ig isotype–switched memory B cells, with the latter only being generated by fully formed GCs. Production of affinity-matured IgM by IgM+CD27+ B cells may protect against pathogens to which a normal immune response is elicited in XLP patients.

Authors

Cindy S. Ma, Stefania Pittaluga, Danielle T. Avery, Nathan J. Hare, Irina Maric, Amy D. Klion, Kim E. Nichols, Stuart G. Tangye

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Figure 1

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SAP is expressed in human T cells but not B cells. (A) Human tonsil mono...
SAP is expressed in human T cells but not B cells. (A) Human tonsil mononuclear cells were stained with CD20 and CD38 mAbs. T cell (CD20–CD38+; population 1), B cell (CD20+CD38+; population 2), and GC B cell (CD20hiCD38hi; population 3) populations were isolated by cell sorting. Following sorting, the purity of populations 1, 2, and 3 was 98%, 98% and 95%, respectively. (B) Sort-purified tonsillar T cells, B cells, and GC B cells as well as activated PBMCs from a normal donor or an XLP patient (XLP#10; ref. 27) were solubilized in 1% NP-40 lysis buffer in 10 mM Tris-HCl and 150 mM NaCl (pH 7.8) supplemented with protease and phosphatase inhibitors. Lysates containing ∼5–10 × 105 cell equivalents were analyzed for SAP expression by SDS-PAGE and Western blotting using rabbit anti-human SAP polyclonal antiserum (top). Lysates from the human T cell line F2F7 were examined concomitantly, and detection of SHP-2 expression was used to demonstrate equivalent loading of cellular proteins (bottom). Results are representative of data obtained by analyzing sort-purified B cell populations isolated from 3 different donor tonsils. (C and D) Immunohistology was performed on reactive tonsil sections using anti-CD20 mAb (pink/purple) and anti-SAP polyclonal Ab (orange/brown). B cells in the follicle (FO) (CD20+; asterisk) and GC (CD20hi; pound symbol), as well as SAP-expressing non–B cells (caret), are indicated. Boxed region in C (magnification, ×20) is shown in D (magnification, ×40). (E) Sort-purified PB naive and memory B cells were prepared and analyzed for SAP expression as described in A.