Final answer:
Plasma cells are created from activated B cells, which are typically activated with the help of cytokines released by helper T cells upon recognizing an antigen-MHC II complex presented by the B cell.
Step-by-step explanation:
Plasma cells are derived from B cells and are crucial for the body's immune response. These cells are responsible for producing antibodies, which are essential in fighting off pathogens like bacteria and viruses. The activation of a B cell, which precedes the formation of plasma cells, is a complex process that usually requires assistance from helper T cells. When a B cell encounters an antigen, it processes and presents it on its MHC II molecule. A helper T cell then recognizes the MHC II-antigen complex and binds to it, subsequently releasing cytokines.
These signaling molecules activate the B cell, leading it to proliferate and differentiate into more B cells and plasma cells. The final answer to which cell type activates plasma cells is B) T cell.