Final answer:
In the process of T cell-dependent activation, a helper T cell recognizes and binds to an antigen presented on an MHC class II molecule by a B cell. This interaction, assisted by cytokines, fully activates the B cell to differentiate into antibody-producing plasma cells and memory B cells.
Step-by-step explanation:
In order for the helper T cell to stimulate the B cell, both must be activated by the same antigen. This process is called T cell-dependent activation of B cells. It involves multiple steps, where initially a B cell encounters an antigen and through its B cell receptor (BCR), it binds and internalizes it. Following this, the B cell processes the antigen and presents peptides of it on its surface in association with MHC class II molecules.
Once the antigen is presented on MHC class II, the helper T cell, which has a specific receptor for the same antigen, can recognize this MHC II-antigen complex. Upon recognition, the T cell binds to the B cell and becomes activated.
The active helper T cell then secretes cytokines that are essential for the full activation of the B cell, ultimately leading to the B cell differentiation into memory B cells and plasma cells capable of producing antibodies to fight the pathogen.
This sequence of events demonstrates a vital aspect of the adaptive immune response where B and T cells work in concert to create a strong and specific immune defense against pathogens.