In cellular immunity, which statement best describes the final stage of activation?

• A. The Th or Tc cell binds a co-stimulator and becomes activated
• B. The antigen is presented to B cells
• C. The T cell differentiates into memory cells
• D. The activated Th or Tc cell clone proliferates and differentiates into effector cells and memory T cells

Answer: (D)

The final stage of cellular immunity activation is clonal expansion: once a T cell that recognizes its antigen is activated, it proliferates to form a large clone of identical cells. These include effector cells that actively fight the current infection (like cytotoxic T cells and helper T cells) and memory T cells that persist for future encounters. This combination—rapidly expanding effector cells to deal with the present threat plus memory cells for faster responses later—best captures the end stage of T cell activation.

The other statements describe earlier steps or incomplete outcomes. Activation begins with the T cell receptor recognizing antigen plus a co-stimulatory signal, which is not the final stage. Presenting the antigen to B cells relates to humoral immunity rather than the final T cell–driven response. Differentiation into memory cells occurs, but without the accompanying clonal expansion into effector and memory populations, it’s not the full final stage.