|
|
||||||||
CUTTING EDGE |




Department of
*
Medicine and
Department of Microbiology, Columbia University, New York, NY 10032; and
Department of Microbiology & Immunology, Albert Einstein College of Medicine, Bronx, NY 10461
| Abstract |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
Studies of murine systemic lupus erythematosus have demonstrated that all B cell lineages can contribute to an anti-DNA Ab response (7, 8). What determines whether an anti-DNA B cell will mature as a B1, MZ, or follicular cell and whether the same autoreactive B cell can mature to more than one B cell subset is not known. BALB/c mice transgenic for the H chain of an anti-DNA Ab (R4A-
2b) maintain B cell tolerance (9). Transgene-expressing B cells mature normally despite the fact that the H chain is IgG and autoreactive transgene-expressing B cells undergo negative selection. Under hormonal influence, the autoreactive B cells mature to immunocompetence and secrete pathogenic anti-DNA Abs (10, 11). DNA-reactive B cells maturing under estrogenic stimulation become MZ cells (12). DNA-reactive B cells maturing in the context of increased prolactin develop as follicular cells; their survival is T cell-dependent and appears to depend on up-regulation of CD40 and CD40 ligand expression (11). This model provided the opportunity to determine whether the same B cells could acquire either a MZ or follicular phenotype and to investigate factors governing that cell fate decision.
We now demonstrate that identical B cells can become either MZ or follicular cells and that hormonal milieu may be an important determinant of mature B cell differentiation. This observation has implications for the heterogeneous presentation of patients with lupus.
| Materials and Methods |
|---|
|
|
|---|
Female BALB/c mice (814 wk old) from The Jackson Laboratory and 812 wk old female R4A-
2b BALB/c mice bred in a specific pathogen-free barrier facility at the Albert Einstein College of Medicine and Columbia University were used. Mice were ovariectomized before hormonal treatment.
Hormonal treatment
Mice were implanted s.c. with 60-day time release pellets containing placebo, 17
-estradiol (0.18 mg), or prolactin (6 mg) (Innovative Research of America).
Cell surface staining and flow cytometry
Spleen cells were isolated from R4A-
2b BALB/c mice as well as from BALB/c mice treated with estradiol, prolactin, or placebo. RBC were lysed and splenocytes were stained with the following Abs for subset analysis: CD19 (clone 1D3), CD21 (clone 7G6), CD23 (clone B3B4), AA4.1, and IgG2b (clone R12-3) (for R4A-
2b BALB/c mice only) and analyzed by flow cytometry (BD Biosciences). For single-cell sorting, cells were stained for expression of CD19, heat-stable Ag (HSA; CD24), CD21, and CD23. All Abs used in this study were obtained from BD Pharmingen except for AA4.1 (eBioscience).
Sorting of single cells
Cells were sorted using the MoFlo cell sorter (DakoCytomation).
2b+ MZ and follicular B cells were isolated for single-cell PCR as described by Yamagami et al. (13) by directly sorting into 96-well plates (Fisher Scientific) containing 3 µl of PCR buffer (Roche Applied Science) and 7 µl of distilled water. DNA was prepared by the addition of 2 µl of proteinase K (5 mg/ml; Boehringer Mannheim) followed by incubation of cells for 1 h at 55°C and for 10 min at 90°C to inactivate the proteinase K. The plates were stored at 70°C until use for DNA amplification.
Single-cell PCR analysis of
gene rearrangement
DNA amplification from single cells was conducted by two rounds of PCR using a GeneAmp PCR system 9700 PCR machine (Applied Biosystems). V
primers described by Yamagami et al. (13) were used. The first-round PCR contained all of the 5' and 3' primers listed above in a 30-µl reaction volume. PCR amplification conditions were as previously described by Ehlich et al. (14). The PCR products were identified as follows: V
J
1, 650 bp; V
J
2, 280 bp; V
J
4, 600 bp; and V
J
5, 260 bp. An initial analysis of the expressed light chains of B cells in the spleen of an unimmunized mouse showed that the primer set detected multiple V
genes, confirming that these primers were capable of hybridizing to many, if not all, V
sequences.
Cloning and sequencing of PCR products
PCR products were either cloned into the TOPO TA cloning vector (Invitrogen Life Technologies) or directly purified from the agarose gels and sequenced. Nucleotide sequences were determined by Genewiz. Analysis of the DNA sequences was conducted using the BLAST program (
www.ncbi.nlm.nih.gov/blast/
).
Real-time PCR
B cells were isolated from splenocytes by depletion using biotin-labeled anti-CD43 (cloneS7; BD Pharmingen), anti-CD11c (clone HL3; BD Pharmingen), anti-CD90 (clone CT-TH1; Caltag Laboratories), and streptavidin-labeled Dynabeads (Dynal). Splenocyte and B cell RNA was isolated using the RNeasy kit from Qiagen and cDNA was synthesized using the iScript cDNA synthesis kit (Bio-Rad). Real-time PCR was performed by using a MyiQ single-color Real-Time PCR detection system (Bio-Rad). The reactions were performed by using TaqMan universal PCR master mix and TaqMan primers (Applied Biosystems) in a 15-µl final volume. The relative expression of B cell-activating factor (BAFF), BAFF-R, and transmembrane activator and calcium modulator ligand interactor (TACI) was determined in comparison to Polr2a, and data were analyzed using the Pfaffl method (15). ABI primer identifications for BAFF, BAFF-R, TACI, and Polr2a were Mm00446347_m1, Mm00840578_m1, Mm00840192_m1, and Mm00839493_m1, respectively.
Calcium influx
Splenocytes from BALB/c mice treated with estradiol, prolactin, or placebo pellets (five mice in each group) were loaded with Indo-1 AM ester (5 µg/ml; Molecular Probes) for 1 h at 37°C. The cells were then stained for CD19, CD21, CD23, and AA4.1. Calcium influx was measured by the MoFlo cell sorter following stimulation with anti-IgM Ab (20 µg/ml; Southern Biotechnology Associates) using the following lasers: UV, blue (488 nm), green (543 nm), and red (633635 nm). Similarly, phospho-ERK1/2 expression was determined by flow cytometry using an LSR II (BD Biosciences) and Abs to B220, CD24, and phospho-ERK1/2 from BD PharMingen. Analysis was performed using FlowJo software (Tree Star).
Statistical analysis
Data were analyzed with standard statistical tests (mean value, SD, and two-tailed Students t test).
| Results |
|---|
|
|
|---|
The R4A-
2b mice are transgenic for the IgG2b H chain of an anti-DNA Ab. Maturation of the transgene-expressing B cells is normal and allelic exclusion is maintained in naive B cells. In R4A-
2b mice, >90% of the B cells express endogenous H and L chains; the remaining 510% of B cells express a
2b H chain (9). In previous studies, we were unable to identify IgG2b-expressing B cells that were not expressing the transgene-encoded H chain (16, 17, 18, 19). The R4A H chain can pair with a large spectrum of endogenous L chains, resulting in B cells with a spectrum of reactivity to DNA. Certain L chains associate with the R4A H chain to form high-affinity anti-DNA Abs; other L chains encode low-affinity anti-DNA Abs (16, 17, 18). Low-affinity DNA-reactive B cells mature to immunocompetence, but high-affinity DNA-reactive B cells arising in the bone marrow are deleted.
When R4A-
2b mice are treated with exogenous estradiol to maintain a constant serum concentration of
75 pg/ml, which is similar to estradiol levels present at the peak of the estrous cycle, or with exogenous prolactin which causes a doubling in serum concentration (50 ng/ml vs 2035 ng/ml), high-affinity autoreactive B cells mature to immunocompetence and secrete anti-DNA Abs (10, 11). In estrogen-treated mice, MZ B cells produce the anti-DNA Ab, whereas in prolactin-treated mice follicular B cells are responsible for autoantibody production (11, 20). We, therefore, were able to ask whether the same DNA-reactive B cells are present in both mature subsets.
Hormonal treatment did not alter the total splenic B cell number (Table I). There was a decrease in T1 cells in both estradiol- and prolactin-treated mice (AA4.1+, CD21, CD23) but no overall decrease in mature B cells, although estradiol led to an anticipated expansion of MZ cells (Table I). As shown in Fig. 1, sorting for both MZ and follicular B cells (HSAlow, CD21high, CD23 and HSAlow, CD21int, CD23high, respectively) yielded populations with >95% purity (Fig. 1). The transgene-expressing MZ cells isolated from estradiol-treated mice expressed a fairly restricted spectrum of L chains (Table II). Only four L chains were detected among 36 sequences; all were known to encode DNA reactivity in association with the R4A H chain. Three V-J combinations encoded high-affinity DNA binding. The fourth L chain, V
1A-J
5, encoded a low-affinity, nonglomerular-binding anti-DNA Ab which is normally not subject to tolerance induction.
|
|
|
1A-J
5 L chains were found in the follicular population of prolactin-treated mice. A population with V
21E-J
5 L chains and unknown antigenic specificity was present. Transitional B cells from estradiol- and prolactin-treated mice differ in BCR signaling
A number of recent studies have suggested that the strength of BCR signaling is key to determining the phenotype of the mature B cell (21, 22) with MZ B cells induced by weak BCR signaling and follicular B cells induced by stronger signaling. We, therefore, investigated whether hormonal treatment altered BCR signaling. As previously demonstrated (20), estradiol led to a diminished calcium flux in transitional B cells following incubation with anti-IgM Ab which was used as a surrogate Ag (Fig. 2A). Prolactin, however, did not alter BCR signaling (Fig. 2B). Thus, transitional B cells from estradiol-treated mice displayed a diminished calcium flux compared with transitional B cells of prolactin-treated mice (Fig. 2C). The decrease in calcium flux in estradiol-treated cells was evident in both the T1 and T2 subset (Fig. 2D). ERK1/2 phosphorylation following incubation with anti-IgM Ab was less in transitional cells of estradiol-treated mice than in prolactin-treated mice (Fig. 2E), while there was no difference in Syk phosphorylation (data not shown).
|
| Discussion |
|---|
|
|
|---|
Studies of altered B cell subsets have not addressed the antigenic specificities of cells in different B cell compartments. Thus, it is not known whether, when the MZ population is expanded, there is an expansion of anti-polysaccharide B cells within the MZ or whether B cells specific for protein Ags can be made to mature into a T cell-independent subset. Conversely, when the MZ population is diminished, it is not clear whether polysaccharide-specific B cells reside in the follicular compartment. Although studies have shown that B cells with an identical antigenic specificity can mature as either B1 or B2 cells and that this cell fate decision is determined by the strength of the BCR signal (22), no study to date has addressed whether identical B cells can mature as either MZ or follicular cells.
Thien et al. (28) have studied follicular vs MZ B cell development in B cells specific for hen egg lysozyme (HEL). When BAFF is increased, B cells that would normally experience developmental arrest in the presence of HEL become immunocompetent follicular B cells while B cells with lower affinity for HEL become MZ B cells. Although this is consistent with weak BCR signaling leading to MZ development and strong BCR signaling leading to follicular development, the MZ and follicular B cells in this study differ in fine antigenic specificity and cross-reactivity.
We show for the first time that the identical cells mature as either MZ or follicular cells and that antigenic specificity, per se, does not determine the differentiation pathway. Rather, hormonal milieu determines cell fate and BCR signaling strength. DNA-reactive B cells from estradiol-treated mice display increased expression of Bc12; however, by itself, this will favor the generation of follicular B cells (29). Prolactin increases CD40 expression on B cells (11), which we believe mediates their rescue from negative selection; perhaps, it also helps recruit them to a T cell-dependent B cell compartment.
The human lupus population is likely to include individuals with MZ B cells and others with follicular B cells as the source of anti-DNA Ab. Perhaps the autoreactive B cell phenotype might distinguish those patients who develop long-term remissions from those with more recurrent disease. That in different individuals the same Abs may be made by B cells from different B cell subsets, depending on the hormonal milieu, and perhaps on BCR signaling strength, has implications for protective as well as pathogenic Abs.
| Acknowledgments |
|---|
| Disclosures |
|---|
|
|
|---|
| Footnotes |
|---|
1 This work was supported by grants from the National Institutes of Health. ![]()
2 Address correspondence and reprint requests to Dr. Betty Diamond, Department of Medicine, Columbia University, Audobon III Building, 9th Floor, Room 916, New York, NY 10032. E-mail address: bd2137{at}columbia.edu ![]()
3 Abbreviations used in this paper: MZ, marginal zone; HSA, heat-stable Ag; BAFF, B cell-activating factor; TACI, transmembrane activator and calcium modulator ligand interactor; HEL, hen egg lysozyme. ![]()
Received for publication September 7, 2005. Accepted for publication January 10, 2006.
| References |
|---|
|
|
|---|
/ small pre-BII cells have no L chain gene rearrangements: detection by high-efficiency single cell PCR. Immunity 11: 309-316. [Medline]This article has been cited by other articles:
![]() |
J. Zhang, R. Sun, and Z. Tian Human Prolactin Promotes Human Secondary Immunoglobulin Response in Human/SCID Mouse Chimeras Clin. Vaccine Immunol., January 1, 2007; 14(1): 60 - 64. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |