Final answer:
B cells require two signals for activation: antigen recognition via surface immunoglobulin and cytokine signaling from a T helper cell. The helper T cell provides the second signal through interaction with MHC II on the B cell after recognizing the presented antigen with its TCR.
Step-by-step explanation:
The activation of resting B cells by T helper cells is a multi-step process that involves costimulatory interactions for a full immune response.
Initially, B cells bind to an antigen through their surface immunoglobulin and internalize it. The antigen is then processed and presented on the B cell's surface using a class II MHC molecule.
For complete activation, B cells require two signals: one from their surface immunoglobulin recognizing the antigen and another from the T cell's cytokines, after the T cell engages the presented antigen with its T-cell receptor (TCR).
Helper T cells interact with the presented antigen on the B cell through the TCR and the CD4 molecule's interaction with the B cell's MHC II. This linked recognition is crucial for the activation of the B cell.
Once the B cell is activated by the helper T cell, it proliferates and differentiates into memory B cells and plasma cells. Cytokines secreted by the helper T cell, following the TCR recognition, act as the second signal resulting in full B cell activation.