Final answer:
NK cells do not undergo clonal expansion; this process is specific to B and T lymphocytes of the adaptive immune system, which proliferate in response to their antigen receptors binding to an antigen.
Step-by-step explanation:
The question of whether NK cells undergo clonal expansion elicits a false response. Clonal expansion is a process typically associated with B and T lymphocytes in the adaptive immune system. These cells are known to undergo clonal expansion when their specific antigen receptors recognize and bind to an antigen. Following this binding, the B and T cells proliferate, creating multiple copies or 'clones' that act against the specific antigen. According to the clonal selection theory proposed by Frank Burnet in the 1950s, clonal expansion is crucial because it helps increase the numbers of specific cells (answer d to question 16) that are equipped to fight the antigen.
Natural killer (NK) cells differ in that they are part of the innate immune system and do not have highly variable, antigen-specific receptors like B and T cells. Instead, they recognize stressed cells in the absence of antibodies and MHC, and therefore do not undergo clonal expansion in the same way that B or T cells do.