B cell zone reticular cell microenvironments shape CXCL13 gradient formation.

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Morphogens establish concentration gradients to control cell behavior in tissues.
• Chemokines, like CXCL13, are key signaling molecules in immune cell trafficking.

Purpose of the Study:

• To investigate how the chemokine CXCL13 forms gradients and influences B cell trafficking.
• To elucidate the role of follicular reticular cells and cathepsin B in CXCL13 gradient formation and B cell homing.

Main Methods:

• Computer simulations and optimization analysis to predict gradient formation.
• In situ imaging analysis to visualize CXCL13 binding to the extracellular matrix.
• Analysis of mice lacking the protease cathepsin B to assess follicular architecture and B cell homing.

Main Results:

• CXCL13 forms both soluble and immobilized gradients, mediated by follicular reticular cells organized in a network.
• Immobilized CXCL13 gradients, constrained by extracellular matrix binding, are predicted to enhance B cell trafficking.
• Cathepsin B is required for CXCL13 solubilization; its absence leads to abnormal follicular architecture and impaired B cell movement within lymph nodes.

Conclusions:

• Reticular cells create microenvironments that shape both immobilized and soluble CXCL13 gradients.
• These gradients are critical for regulating B cell homing and intra-lymph node trafficking.
• The interplay between immobilized and soluble CXCL13, regulated by cathepsin B, is essential for maintaining lymph node structure and function.