Final answer:
Clonal selection is a process where specific lymphocytes multiply in response to an antigen, leading to a polyclonal response and clonal expansion of activated B and T cells, which are then equipped to effectively fight off infection.
Step-by-step explanation:
The process of clonal selection best describes the phenomenon where lymphocytes that can recognize and react to a specific antigen proliferate. During this process, only those clones of B or T cells with receptor specificity for the antigen are stimulated to divide, leading to a polyclonal response involving multiple T cell clones. Following activation, these selected clones expand in number, producing large quantities of identical lymphocytes equipped to combat the infection.
Clonal expansion is vital for both B cell and T cell populations. In B cells, this results in plasma cells that secrete antibodies with antigen specificity identical to the B cells selected. Meanwhile, for T cells, upon activation through antigen binding, they undergo rapid mitotic division, expanding and forming numerous identical clones, with each clone retaining the same specific antigen receptor.