The cellular response
T lymphocytes, or T cells, take part in the specific immune response. Their response to foreign antigens is known as the cellular response and involves cells acting against infected or abnormal body cells.
An antigen-presenting cell displays a foreign antigen at its cell-surface membrane. The antigen is presented with a major histocompatibility complex (MHC).
Activating a specific T cell
Different T cells carry different receptor proteins. An antigen-presenting cell activates a T cell whose receptor has a complementary shape to the antigen being displayed.
- A foreign antigen is displayed at the surface of an antigen-presenting cell.
- A T cell with the appropriate complementary receptor encounters the antigen.
- The receptor binds to the displayed antigen.
- The specific T cell is activated.
Macrophages can act as antigen-presenting cells after phagocytosing and digesting pathogens, allowing the products of the non-specific response to help initiate a specific response.
Exam Tip: In an answer about T-cell activation, include antigen presentation and complementarity: the antigen is displayed at the cell surface and only a T cell with a complementary receptor is activated.