Altered B cells homeostasis in child-onset immunoglobulin A vasculitis

Background Immunoglobulin A vasculitis (IgAV), also called Henoch–Schonlein purpura, is a systemic small vessels vasculitis with immunoglobulin A1-dominant immune deposits. B-cells are a heterogeneous population with unique subsets distinguished by their phenotypes and cytokine production. Here, we explored the status of B cell subsets in patients with IgAV. Methods Thirty IgAV patients and fifteen age- and sex-matched healthy individuals were enrolled in this study. Fresh blood samples were collected from both healthy and IgAV patients. Upon the distinct expressions of CD3, CD19, CD20, CD38, CD27 and IgD, peripheral blood mononuclear cells (PBMCs) were initially categorized into plasmablasts and memory B cells. Subsequently, using surface markers including CD138 and IgM, and intracellular markers containing IgM and IgG, plasmablasts and memory B cells were further divided into distinct subgroups. A total of eleven populations were detected using multiple flow cytometry. Results CD3 - CD19 + IgD + CD27 - , CD3 - CD19 + CD20 - CD38 + , CD3 - CD19 + CD20 - CD38 + IgM + , and CD3 - CD19 + CD20 - CD38 + CD138 + B cells were larger in patients with IgAV than in the HCs. Only CD3 - CD19 + IgD - CD27 + IgM + B cell counts were reduced in IgAV. The elevated B cell numbers returned to normal after treatment. Plasma and plasmablast B cell numbers correlated with plasma IgA levels. On the contrary, CD3 - CD19 + IgD - CD27 + IgM + B cell numbers were negatively proportional to the plasma IgA levels while naive B cell numbers correlated with plasma and plasmablast B cell counts. Conclusions We hypothesized that immunoglobulin production was abnormally elevated in IgAV and could be explained by altered B-cell subset homeostasis.