Final answer:
Follicular helper T-cells mediate B-cell activation by binding to an antigen presented on the MHC II of B cells, causing them to release cytokines that prompt B cell proliferation and differentiation into antibody-producing plasma cells and memory B cells.
Step-by-step explanation:
The activation of B cells is a critical step in the adaptive immune response, and follicular helper T-cells play a significant role in this process. To commence activation, a B cell first engulfs an antigen and processes it. The B cell then presents fragments of this antigen on its surface using molecules called MHC II (Major Histocompatibility Complex class II). A matching follicular helper T-cell, which is specific to the same antigen, recognizes this MHC II-antigen complex and binds to the B cell.
Upon engagement, the helper T-cell becomes activated and subsequently secretes cytokines. These cytokines function as chemical signals that instruct the B cell to proliferate and differentiate into two major types of cells: plasma cells and memory B cells. Plasma cells are specialized in the production and secretion of antibodies, which are crucial for targeting and neutralizing pathogens.
Memory B cells, on the other hand, remain in the body to provide a rapid response upon future exposures to the same antigen, thus contributing to long-term immune memory.
The process described ensures that B cells can effectively multiply and transition into their functional forms, contributing to the humoral arm of the immune system's response to pathogens, and forming an important component of immune memory through the creation of memory B cells.