Question

Explain the mechanism of action of T-cells to antigens.

Answer 1

Like B-lymphocytes, T-cells are also antigen-specific, as each T-cell recognises a specific antigen. Thus, different types of antigens stimulate different types of T-cells.

When a T-cell comes in contact with an antigen, the T-lymphocyte divides rapidly to form a clone of T-cells. A clone of T-cells has four types of cells. These are helper T-cells, killer T-cells, suppressor T-cells, and memory T-cells. Out of these, the first three are also called effector cells. Cytotoxic T-cells or killer T-cells (Tc cells) destroy infected cells having foreign antigens attached to their surface. They become active when they receive signal molecules from helper T-cells and antigen-presenting cells or when they are exposed to foreign antigens. They secrete perforin molecules and granzymes.

1. Perforins form pores in the cell membrane of infected cells. Water and ions enter the infected cells through these pores and cause their bursting.
2. Granzymes enter the infected cells by endocytosis and initiate their apoptosis (cell death), leading to fragmentation of their nucleus and cytoplasm. Memory T-cells are sensitised by antigens and retain sensitisation for the future. Suppressor T-cells inhibit immune response by releasing cytokines that suppress the activity of other T-cells and B-cells. Helper T-cells secrete substances that enhance or activate immune responses.