Final answer:
The statement is false. Activated B cells do not move to the dark zone but rather undergo clonal selection in the light zone of the germinal center, differentiating into plasma cells or memory B cells. There, they interact with follicular dendritic cells, not Langerhans' cells, for further maturation and antigen testing.
Step-by-step explanation:
The statement in the question is false. B cells activated by interactions with helper T cells do not move from the light zone to the dark zone in the germinal center to test their new binding site against antigen on the surface of Langerhans' cells. Instead, once a B cell is activated by a helper T cell in the lymph node, it undergoes a process called clonal selection in the light zone of the germinal center, where it proliferates and differentiates into either plasma cells or memory B cells.
After a B cell engulfs an antigen, it presents fragments of the antigen bound to MHC class II molecules on its surface. This is necessary for the B cell to be recognized by activated helper T cells. Once the helper T cell binds and recognizes the MHC II-antigen complex, it secretes cytokines that signal the B cell to undergo clonal expansion and differentiation. The differentiated plasma cells will produce antibodies specific to the antigen, playing a crucial role in the humoral immune response.
Throughout this process, B cells function as professional antigen-presenting cells (APCs) and do not migrate to the Langerhans' cells to test their newly formed antigen receptors; they undergo affinity maturation and selection within the germinal center. Hence, the interaction and maturation primarily occur in the light zone of the germinal center where follicular dendritic cells, not Langerhans' cells, present the antigen.