Altered B lymphocyte homeostasis and functions in systemic sclerosis

Area of Science:

• Immunology
• Rheumatology
• Cell Biology

Background:

• B-cells play a role in systemic sclerosis (SSc) beyond autoantibody production, potentially through secreting proinflammatory/profibrotic cytokines.
• B-cell subsets are diverse, with varying phenotypes and cytokine profiles, but data on these in SSc are limited.
• Understanding B-cell homeostasis, activation, and signaling is crucial for SSc pathogenesis.

Purpose of the Study:

• To comprehensively analyze B-cell homeostasis, activation, proliferation, and cytokine production in SSc patients.
• To investigate intracellular signaling pathways in B-cells from SSc patients.
• To explore correlations between B-cell alterations, serum cytokines, and disease characteristics.

Main Methods:

• Flow cytometry was used to phenotype B-cell subsets (CD19, CD21, CD24, CD38, CD27, IgM, IgD) and assess activation markers (CD25, CD80, CD95, HLA-DR).
• Intracellular IL-10 and IL-6 production were measured post-stimulation (TLR9, CD40).
• mRNA levels of IL-6, IL-10, Ki67, and Bcl2 were quantified in B-cells.
• Serum and B-cell culture supernatant cytokine levels were assessed using multiplex assays.
• Intracellular signaling pathways (mTOR, ERK, STAT3, STAT5 phosphorylation) were analyzed via flow cytometry.

Main Results:

• SSc patients displayed altered B-cell distribution: decreased memory B-cells and increased naive and CD21^LoCD38^Lo subsets.
• Increased expression of activation markers (CD80, CD95, HLA-DR) was observed on SSc B-cell subsets, particularly memory B-cells.
• Elevated serum levels of IL-6, BAFF, and CXCL13 were found in SSc patients, but without correlation to B-cell subsets.
• A reduced proportion of IL-10 and IL-6 producing B-cells was noted in SSc patients after stimulation.
• Significantly decreased mTOR phosphorylation was observed in B-cells from SSc patients.

Conclusions:

• Systemic sclerosis is characterized by altered B-cell homeostasis, including decreased and activated memory B-cells.
• The reduced capacity for IL-10 production in SSc B-cells is associated with impaired mTOR signaling.
• Serum cytokine profiles did not directly correlate with the observed B-cell homeostasis alterations in SSc.