Cell-mediated immunity (CMI) is an immune response that does not involve antibodies but rather involves the activation of macrophages and NK cells, the production of antigen-specific cytotoxic T lymphocytes, and the release of various cytokines in response to antigen.

T cells are a type of white blood cell that plays a central role in CMI. They are responsible for:

* Recognizing and destroying infected or cancerous cells: T cells have receptors that can recognize specific antigens on the surface of infected or cancerous cells. When they encounter these cells, they activate a process called apoptosis, which leads to the death of the target cell.

* Activating other immune cells: T cells can also release cytokines, which are signaling molecules that can activate other immune cells, such as macrophages and NK cells.

Types of T cells involved in CMI:

* Cytotoxic T lymphocytes (CTLs): Directly kill infected or cancerous cells.

* Helper T cells (Th cells): Help activate other immune cells, including CTLs, macrophages, and B cells.

Mechanism of CMI:

1. Antigen presentation: Antigen-presenting cells (APCs), such as macrophages and dendritic cells, engulf and process antigens.

2. T cell activation: APCs present the antigens to T cells, activating them.

3. Clonal expansion: Activated T cells proliferate and differentiate into effector T cells.

4. Target cell destruction: CTLs kill infected or cancerous cells, while Th cells provide help to other immune cells.

Summary:

Cell-mediated immunity is a critical part of the immune system that relies on T lymphocytes to recognize and destroy infected or cancerous cells, as well as to activate other immune cells.