Date Published: March 31, 2016
Publisher: Public Library of Science
Author(s): Xintong Hu, Jiandong Tai, Zhihui Qu, Songchen Zhao, Li Zhang, Man Li, Xiguang Sun, Yanfang Jiang, Menno C van Zelm.
Henoch—Schoenlein purpura is the one of most common types of systemic vasculitis that involves impaired renal function and Henoch-Schoenlein purpura nephritis (HSPN). The diagnosis of this condition is largely based on immunohistologic detection of immunoglobulin A1-containing immune complex in the glomerular deposits of mesangium. Despite clinical advances, the etiopathogenesis of HSPN is still largely unknown.
In this study, we enrolled 25 newly diagnosed HSPN patients and 14 healthy controls. Then, fractions of B cell subtypes were determined in venous blood using flow cytometry. The serum interleukin (IL)-10 concentration was determined by enzyme-linked immunosorbent assay.
Compared to those in healthy controls, the numbers of CD38+CD19+, CD86+CD19+, CD38+CD86+CD19+, and CD95+CD19+ B cells per microliter of blood were significantly higher in HSPN patients. In contrast, the numbers of CD5+CD19+, IL-10+CD19+, CD5+CD1d+CD19+, and IL-10+CD5+CD1d+CD19+ B cells per microliter of blood and the serum IL-10 concentration were significantly lower in HSPN patients. Following treatment, the numbers of CD38+CD19+ and CD86+CD19+ B cells per microliter of blood were significantly reduced in HSPN patients. However, the numbers of CD5+CD1d+CD19+, CD5+CD1d+IL-10+CD19+, and IL-10+CD19+ B cells per microliter of blood and the serum IL-10 concentration were significantly increased in HSPN patients following treatment. The estimated glomerular filtration rate (eGFR) was negatively correlated with the number of CD38+CD19+ B cells but positively correlated with the numbers of IL-10+CD19+, CD1d+CD5+CD19+, and IL-10+CD1d+CD5+CD19+B cells per microliter of blood and the serum IL-10 concentration. The 24-h urinary protein concentration was positively correlated with the number of CD38+CD19+B cells but negatively correlated with the numbers of IL-10+CD19+, CD1d+CD5+CD19+, and IL-10+CD1d+CD5+CD19+B cells per microliter of blood and the serum IL-10 concentration.
Our results suggest that CD38+CD19+ and CD1d+CD5+CD19+ B cells (Bregs) contribute to the pathogenesis of HSPN.
Henoch—Schoenlein purpura (HSP) is a systemic vasculitis that affects small vessels. In this condition, patients develop perivascular inflammatory cell infiltrates. It is an immunoglobulin A-related immune complex-mediated disease that adversely affects the skin, joints, and gastrointestinal system, especially the kidney [1,2]. In recent studies, it has been reported that glomerular damage occurs in patients with HSPN, and such damage might be due to the deposition of mesangial Gd-IgA1-containing immune complex, which acts as a potential mediator via mesangial receptors. Subsequently, complement-mediated stimulation of mesangial cells occurs, leading to their proliferation. Moreover, cytokine secretion is also stimulated under such circumstances . However, IgA deposition recurs in some patients even after they undergo renal transplantation [4,5]. In such patients, we detect mild forms of IgA nephropathy (IgAN), because there is deposition of immune complex and nephritic changes . As a result, we usually detect an extrarenal source of antigen and an antibody immune complex in these patients. Furthermore, B cells are divided into different subsets depending on the presence of surface molecules. In the peripheral blood, naive and memory B cells express different amounts of CD27 . This indicates that activated CD27+ B cells can establish memory responses . Activated B cells can differentiate into CD38+ plasma cells that secrete antibodies [9,10] and cytokines, which enhance the expression of co-stimulation molecules, especially CD86 (which is an established marker of B-cell activation) and CD95 [11,12]. The CD95 receptor is considered to be a key regulator in the activation of germ cell apoptosis . These different subtypes of B cells are known to collaborate and control the responses of the human immune system; however, very little information is available regarding the mechanisms governing the onset of HSPN in patients.
Previous studies have failed to clarify the pathogenesis of HSPN. However, they have proved that HSPN is mainly associated with glomerular deposits of an immune complex containing IgA. These deposits are primarily found in mesangium. Moreover, the deposition of IgA occurs again in some patients who have previously undergone renal transplantation . In our study, we have characterized the roles of different subsets of peripheral blood B cells in HSPN patients and HCs. In our study, the different B cell subsets were defined as CD38+CD19+, CD86+CD19+, CD38+CD86+CD19+, CD27+CD19+ (activated B cells), CD27-CD19+ (naive B cells), CD95+CD19+, and CD27+CD95+CD19+B cells. Thereafter, we analyzed the numbers of these cells per microliter of blood. We found that compared to those in HCs, the numbers of CD38+CD19+, CD86+CD19+, CD38+CD86+CD19+, and CD95+CD19+B cells were significantly higher in patients with HSPN. However, there were no significant differences in the numbers of CD27+CD19+ and CD27+CD95+CD19+ B cells between the experimental and control groups. The high expression of CD86, which activates CD4+ T cells, indicates the activation of B cells . Activated B cells can also secrete cytokines and express co-stimulatory molecules, such as CD86 and CD95 . Furthermore, it has been proposed that CD95 acts as a key regulator in the activation of germ cell apoptosis . This feedback regulation can maintain the homeostasis of B cells in HSPN patients. We also analyzed the associations between clinical parameters and the numbers of B cells of different subtypes per microliter of blood. We found that 24-h proteinuria is positively correlated with the number of CD38+CD19+ B cells, whereas eGFR is negatively correlated with the number of CD38+CD19+ B cells. Furthermore, the numbers of CD38+CD19+ and CD86+CD19+ (activated) B cells were significantly reduced after treatment. Consequently, the number of circulating CD86+CD19+ B cells, specifically CD38+CD19+ B cells, may be associated with the pathogenesis of HSPN.