Altered BCR signalling quality predisposes to autoimmune disease and a pre-diabetic state

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Spleen tyrosine kinase (Syk) and Zeta-chain associated protein kinase 70 (Zap-70) are key signaling molecules in immune cells.
• These kinases have overlapping expression during lymphocyte development, suggesting functional redundancy but also potential specialization.

Purpose of the Study:

• To investigate the differential in vivo kinase function of Syk and Zap-70.
• To understand the impact of altered B cell receptor (BCR) signaling quality on immune cell development and autoimmune predisposition.

Main Methods:

• Generation of knock-in mice with Zap-70 cDNA replacing Syk, controlled by Syk promoter elements.
• Analysis of B cell selection, survival, and activation pathways (e.g., Erk1/2, ITAM, hemITAM, FcγR).
• Assessment of immune repertoire, autoantibody production, and development of autoimmune conditions.

Main Results:

• Zap-70 replacement for Syk severely impaired B cell survival and selection, highlighting dependence on BCR signaling quality.
• Platelet and neutrophil activation via ITAM and hemITAM pathways were abolished, while macrophage FcγR-mediated phagocytosis was retained.
• Altered BCR signaling led to preferential marginal zone B cell development, autoreactivity (anti-insulin antibodies), glomerulonephritis, and glucose intolerance.

Conclusions:

• BCR signaling quality is critical for proper B cell selection and preventing autoimmunity.
• Aberrant B cell selection due to altered BCR signaling may contribute to autoimmune diseases like type 1 diabetes.
• This study provides insights into the specific roles of Syk and Zap-70 in immune signaling and autoimmune disease pathogenesis.