Role of CD40L
In germinal centers, antigen-experienced TFH cells rapidly upregulate the expression of CD40L, which binds with B cell surface protein CD40 in B cell-T cell zone vicinity. The TFH cell CD40L and B cell CD40 crosstalk modulates the intracellular receptor and gene expression inside the B cell, including induction of AID (Activation-Induced Cytidine Deaminase). AID (AICDA) expression causes B cell antibodies to class switch from IgM/IgD to other antibody isotopes and drives somatic hypermutation during clonal proliferation. The switched antibodies acquire better effector functions, and hypermutated antibody shows greater affinity for antigen. The exact mechanism of AID-mediated B cell maturation is not clear.
Read more about this topic: Follicular B Helper T Cells
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