What can be correctly concluded about this peripheral T lymphocyte? A peripheral T-helper lymphocyte engages peptide-bound class II major histocompatibility complex molecules on the surface of an antigen-presenting cell (APC). No other contact is made between cell surface molecules present on the T lymphocyte and the APC.

The T lymphocyte will undergo anergy

The correct answer is D. This is a phenomenon known as peripheral tolerance. It is an important factor because deletion of self-reactive T lymphocytes within the thymus (central tolerance) is not completely efficient at removing all self-reactive T lymphocytes. Thus, one mechanism of peripheral tolerance is that of anergy: When a T lymphocyte receives the first signal (peptide-major histocompatibility complex) but no second signal (costimulation, such as CD28-B7 ligation), that T lymphocyte undergoes a reprogramming known as anergy, wherein it is subsequently made refractory to any future stimulation. Note that an anergic T lymphocyte cannot be activated later even if costimulation is present Answer A is incorrect. For a T lymphocyte to become activated and fully able to perform its effector functions, it must receive a second or costimulatory signal. Without a costimulatory signal, the T lymphocyte cannot be activated and instead becomes anergic Answer B is incorrect. A T lymphocyte that becomes anergic does not undergo activation Answer C is incorrect. Causing cells to undergo apoptosis is a function of an activated Tcytotoxic lympocyte Answer E is incorrect. The T lymphocyte will not clonally expand. Clonal expansion is more typical of B lymphocytes and requires a costimulatory signal to first activate the lymphocyte.