Circulating plasmablasts/plasma cells: a potential biomarker for IgG4-related disease

Abstract

Background: Immunoglobulin G4 (IgG4)-related disease (IgG4-RD) is a multisystem fibroinflammatory disease. We previously reported that a circulating cell population expressing CD19⁺CD24^-CD38^hi was increased in patients with IgG4-RD. In this study, we aimed to document that this cell population represented circulating plasmablasts/plasma cells, to identify the detailed phenotype and gene expression profile of these IgG4-secreting plasmablasts/plasma cells, and to determine whether this B-cell lineage subset could be a biomarker in IgG4-related disease (IgG4-RD).

Methods: A total of 42 untreated patients with IgG4-RD were evaluated. Peripheral B-cell subsets, including CD19⁺CD24^-CD38^hi plasmablasts/plasma cells, CD19⁺CD24⁺CD38^- memory B cells, CD19⁺CD24^intCD38^int naïve B cells, and CD19⁺CD24^hiCD38^hi regulatory B cells, were assessed and sorted by flow cytometry. Microarray analysis was used to measure gene expression of circulating B-cell lineage subsets. Further characterization of CD19⁺CD24^-CD38^hi plasmablasts/plasma cells was carried out by evaluating additional surface markers, including CD27, CD95, and human leukocyte antigen (HLA)-DR, by flow cytometric assay. In addition, various B-cell lineage subsets were cultured in vitro and IgG4 concentrations were measured by cytometric bead array.

Results: In untreated patients with IgG4-RD, the peripheral CD19⁺CD24^-CD38^hi plasmablast/plasma cell subset was increased and positively correlated with serum IgG4 levels, the number of involved organs, and the IgG4-related Disease Responder Index. It decreased after treatment with glucocorticoids. Characterization of the plasmablast/plasma cell population by gene expression profiling documented a typical plasmablast/plasma cell signature with higher expression of X-box binding protein 1 and IFN regulatory factor 4, but lower expression of paired box gene 5 and B-cell lymphoma 6 protein. In addition, CD27, CD95, and HLA-DR were highly expressed on CD19⁺CD24^-CD38^hi plasmablasts/plasma cells from patients with IgG4-RD. Furthermore, CD19⁺CD24^-CD38^hi plasmablasts/plasma cells secreted more IgG4 than other B-cell populations.

Conclusions: Circulating CD19⁺CD24^-CD38^hi plasmablasts/plasma cells are elevated in active IgG4-RD and decreased after glucocorticoid treatment. This IgG4-secreting plasmablast/plasma cell population might be a potentially useful biomarker for diagnosis and assessing response to treatment.

Keywords: Autoimmunity; Biomarker; CD19+CD24−CD38hi plasmablast/plasma cell; IgG4-RD.

Fig. 1

The correlations of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells with clinical and laboratory parameters. a Gating strategy of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells. Correlations of the ratio of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells and serum (b) immunoglobulin G4 (IgG4), (d) erythrocyte sedimentation rate (ESR), (e) IgG, (f) IgE, (g) C-reactive protein (CRP), and (h) involved organs are shown. c Correlation of the absolute number of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells and serum IgG4. SSC Side scatter

Fig. 2

Gene expression of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells, regulatory B cells (Bregs), memory B cells, and naïve B cells in patients with immunoglobulin G4-related disease (IgG4-RD). B-cell subsets were sorted from the peripheral blood of patients with IgG4-RD, and total RNA was extracted for microarray analysis. The differences among CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells and other B-cell subsets are shown. Columns from left to right represent CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells, CD19⁺CD24^intCD38^int naïve B cells, CD19⁺CD24⁺CD38⁻ memory B cells, and CD19⁺CD24^hiCD38^hi Bregs, respectively. Red represents overexpressed genes, and blue represents underexpressed genes

Fig. 3

The major transcription factors regulating B-cell differentiation into plasma cells. Analysis of transcription factor expression regulating B-cell differentiation into plasma cells. Bars A to D indicate CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells, regulatory B cells, memory B cells, and naïve B cells, respectively. *Difference of more than twofold by comparison of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells with other B-cell subsets

Fig. 4

Expression of HLA class II genes in CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells, regulatory B cells, memory B cells, and naïve B cells

Fig. 5

Expression of proliferation genes, homing genes, and immunoglobulin genes in different B-cell subsets. B-cell proliferation genes, homing genes, and immunoglobulin genes were analyzed in B-cell subsets in patients with immunoglobulin G4-related disease. a to l illustrate genes differently expressed in B cell subsets. Bars A to D indicate CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells, regulatory B cells, memory B cells, and naïve B cells, respectively. *Difference of more than two fold by comparison of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells with other B-cell subsets

Fig. 6

The phenotypic analysis of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells determined by flow cytometry. CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells were gated and then analyzed by flow cytometry. Red represents isotype control, and blue represents the expression level by CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells. BAFF B-cell activating factor, BCMA B-cell maturation antigen, Ig Immunoglobulin, IL-6R Interleukin-6 receptor, TACI Transmembrane activator CAML (calcium modulator and cyclophilin ligand) interactor

Fig. 7

The secretion of immunoglobulin by regulatory B cells (Bregs), CD19⁺C24⁻CD38^hi plasmablasts/plasma cells, memory B cells, and naïve B cells. B-cell subsets, including CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells, Bregs, memory B cells, and naïve B cells from peripheral blood of patients with immunoglobulin G4-related disease (IgG4-RD) were sorted by flow cytometry and underwent cell culture in vitro. After 7 days of cell culture with CD40L and CpG ODN 2006, the supernatants were collected, and immunoglobulin secretion was analyzed. Horizontal histogram illustrates (a) IgG4, (b) IgG, (c) IgE, and (d) IgM secreted by four subsets of B cells. Columns A–D represent Bregs, CD19⁺C24⁻CD38^hi plasmablasts/plasma cells, memory B cells, and naïve B cells, respectively. e Flow diagram of a representative patient with IgG4-RD. (*: P <0.05, **: P <0.01, ***: P <0.001)

Fig. 8

The association between CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells and disease activity. a and b Correlations of the ratio of CD19⁺CD24⁻CD38^hi cells/CD19⁺ B cells and the absolute number of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells with IgG4-related Disease Responder Index (IgG4-RD RI) before treatment. c Change of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells before and after treatment. d–h Ratios of CD19⁺CD24⁻CD38^hi cells/CD19⁺ B cells, absolute number of CD19⁺CD24⁻CD38^hi plasmablasts/plasma cells, IgG4-RD RI, IgG, and IgG4 before and after treatment. *** P < 0.001, **** P < 0.0001