What occurs when a T cell encounters a peptide fragment from a foreign protein?

• A. The T cell remains inactive
• B. The T cell starts to differentiate
• C. The T cell begins an immune reaction
• D. The T cell destroys the protein

Answer: (C)

When a T cell encounters a peptide fragment from a foreign protein, it typically initiates an immune reaction. This process is a crucial part of the adaptive immune response. T cells have specific receptors that recognize these peptide fragments presented on the surfaces of antigen-presenting cells, such as dendritic cells, macrophages, and B cells.

Upon recognition of the foreign peptide, the T cell becomes activated. This activation triggers a cascade of events, leading to the proliferation and differentiation of T cells. Some of these activated T cells will become effector cells, which are responsible for conducting immune responses. Helper T cells assist other immune cells, while cytotoxic T cells can directly kill infected or cancerous cells.

The immune reaction initiated by T cell activation includes the production of signaling molecules known as cytokines, which enhance the immune response and orchestrate the activities of other immune cells. Therefore, the recognition of a peptide fragment by a T cell is a pivotal moment that sets off a well-coordinated immune response to eliminate the foreign intruder.