Elsevier

Clinical Immunology

Volume 132, Issue 3, September 2009, Pages 362-370
Clinical Immunology

T cell CD40LG gene expression and the production of IgG by autologous B cells in systemic lupus erythematosus

https://doi.org/10.1016/j.clim.2009.05.011Get rights and content

Abstract

CD40 ligand (CD40LG), encoded on the X chromosome, has been reported to be overexpressed on lupus T cells. Herein, we investigated the effect of DNA demethylation on T cell CD40LG expression and the production of IgG by autologous B cells in lupus. We found normal human T cells transfected with CD40LG induced autologous B cell activation and plasma cell differentiation. Both female lupus CD4+ T cells and demethylating agents treated CD4+ T cells overexpressed CD40LG mRNA. Further, lupus T cells from both genders or demethylated CD4+ T cells from healthy women overstimulated autologous B cells, and this could be reversed with anti-CD40LG Ab in only females. We demonstrated that female lupus CD4+ T cells and demethylated CD4+ T cells express high level of CD40LG and overstimulate B cells to produce IgG. This is due to DNA demethylation and thereby reactivation of the inactive X chromosome in female.

Introduction

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by antibody production to a variety of nuclear autoantigens [1]. The disease has a strong gender bias with a female:male ratio of 9:1 [2], [3]. Pathogenic autoantibodies synthesized by B lymphocytes are due to the activation of both B and T lymphocytes. One of the important T–B collaboration is the interaction of costimulatory receptor/ligand pairs, CD40–CD40LG.

The interaction between CD40LG and CD40 is important for T cell-dependent immune response. CD40LG, encoded on X chromosome, is a type II membrane protein which belongs to the tumor necrosis factor family [4], [5]. CD40LG is mainly expressed on the surface of activated CD4+ T cells and binds to CD40 on B cells to provide a necessary signal for initiation of immune response, including B cell activation, differentiation and production of pathogenic autoantibodies [6]. Elevated soluble CD40LG in sera and overexpressed CD40LG on T lymphocytes were observed in human and murine lupus [7], [8], [9]. Protein overexpression or gene activation may be caused by gene-specific DNA demethylation or hypomethylation [10]. In vitro, gene demethylation could be induced by DNA methyltransferase inhibitors such as 5-azaC and procainamide, or hydralazine and PD98059 which decrease DNA methyltransferase expression by inhibiting ERK pathway signaling [11], [12], [13]. Recently, we showed that CD40LG was demethylated on CD4+ T cells from women with lupus indicating the reactivation of the inactive X chromosome in female lupus [14]. Therefore, DNA demethylation reactivates CD40LG gene in the silenced X chromosome on T cells and overstimulates B cells to produce a large amount of autoantibodies. We hypothesize that the expression of CD40LG on CD4+ T cells may differ in SLE patients and normal subjects, in demethylating agents treated T cells and untreated normal cells, and overexpression of CD40LG may cause a high level of IgG production by T–B interaction. Furthermore, those differences may be different between women and men if the inactive X chromatin reactivation happened in CD4+ T cells from female lupus.

In the present study, we transfected normal T cells with CD40LG to induce autologous B cell activation and plasma cell differentiation in vitro. Expression of CD40LG mRNA on CD4+ and CD8+ T cells from patients with lupus were detected. We also measured IgG production by coculturing autologous B cells with T cells from lupus patients with or without CD40LG blockage by anti-CD40LG antibody. Similar experiments were performed on T cells from healthy subjects with or without treatment of DNA methylation inhibitors. The differences between the two genders were compared respectively.

Section snippets

Subjects

The subjects recruited in this study include 15 lupus patients (6 women, 9 men; 23.2 ± 5.27 years) and 11 age-, sex-matched healthy controls (6 women, 5 men; 26.9 ± 3.83 years). All patients satisfied at least 4 criteria for lupus classification from the American College of Rheumatology and was assessed by disease activity based on SLE Disease Activity Index (SLEDAI) [15]. There was no difference in SLEDAI scores between female patients and male patients (P > 0.05). Relevant clinical information is

CD40LG overexpression in human T cells results in autologous B cell activation and plasma cell differentiation in vitro

To determine if CD40LG overexpression is sufficient to induce B cell activation and plasma cell differentiation, we transfected primary T cells from normal human donors with CD40LG cDNA cloned into the expression vector pEGFP-C1 (pEGFP-C1/CD40LG). Controls included cells transfected with the empty vector. Transfection efficiency (≥ 40%) was confirmed by flow cytometry for the GFP protein. CD40LG overexpression was confirmed in transfected T cells by flow cytometry using a fluorochrome conjugated

Discussion

Systemic lupus erythematosus (SLE) is a female predominant autoimmune disease with overproduction of various autoantibodies. The CD40LG–CD40 interaction between T and B lymphocytes plays a key role in this pathological process. CD40LG, encoded on the X chromosome, is overexpressed on T cells in lupus patients. Whether CD40LG overexpression on T cells is sufficient to induce T cell autoreactivity and whether CD40LG overexpression is associated with women susceptibility to SLE are not clear. The

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 30730083 and No. 30671883), the National Basic Research Program of China (973 Program) (No. 2009CB825605) Hunan Natural Science Foundation (No. 06C0049) and the Science Foundation of Hunan Province (No. 06SK3033) (QL); and NIH Grant Number P20-RR015577 from the National Center for Research Resources, NIH Grant Number R03AI076729 from the National Institute of Allergy and Infectious Diseases, and funding from the

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    Ying Zhou and Jun Yuan contributed equally to this work.

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