Constitutive CD40 Signaling Calibrates Differentiation Outcomes in Responding B Cells via Multiple Molecular Pathways

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• CD40 signaling inhibits B cell terminal differentiation and promotes memory generation.
• Blimp-1 is crucial for plasma cell (PC) generation, but mechanisms by which CD40 signaling inhibits its induction are unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms by which CD40 signaling inhibits Blimp-1 induction and plasma cell generation.
• To investigate the role of CD40 signaling in regulating the unfolded protein response (UPR) during B cell activation.

Main Methods:

• Investigated the effects of CD40 signaling on Blimp-1, miR-125b, Hrd1, and UPR components (IRE-1α) in B cells.
• Utilized B cells from CD40-CD154 interaction-deficient mice and subjected wild-type B cells to CD40 ligation during LPS stimulation.

Main Results:

• CD40 signaling induces miR-125b to target Blimp-1 transcripts and increases Hrd1 to degrade Blimp-1 protein.
• CD40 signaling inhibits the early UPR by targeting IRE-1α via Hrd1.
• Noncognate CD40 ligation repressed Blimp-1, and CD40 deficiency led to increased Blimp-1 and enhanced differentiation.

Conclusions:

• CD40-mediated inhibition of PC generation involves repression of Blimp-1 and UPR.
• Constitutive CD40 signaling, including bystander T-B interactions, calibrates B cell differentiation outcomes in vivo.