Definition:

Cell-Mediated Immunity (CMI) is a type of immune response in which immune cells play a crucial role in identifying and destroying infected or abnormal cells in the body.

Overview:

CMI is one of the two major branches of the immune system, the other being humoral immunity. It involves the activation of various types of immune cells, such as T lymphocytes (T cells), natural killer (NK) cells, and phagocytes, to defend the body against intracellular pathogens, cancer cells, and foreign tissue.

Mechanism:

During CMI, T cells play a central role in recognizing specific antigens presented by infected or abnormal cells. This recognition triggers the activation and proliferation of T cells, leading to the development of effector T cells and memory T cells. Effector T cells then directly attack the infected or abnormal cells, either by releasing cytotoxic molecules or by activating other immune cells to further destroy the target cells.

Functions of CMI:

1. Elimination of intracellular pathogens: CMI is highly effective in combating viruses, intracellular bacteria, and parasites that take residence inside the body’s cells, preventing their replication and spread.

2. Defense against cancer cells: CMI plays a critical role in the surveillance and elimination of cancer cells. T cells specifically recognize and target malignant cells, inhibiting their growth and preventing the development of tumors.

3. Rejection of transplanted tissue: CMI contributes to the immune rejection of transplanted organs or tissues, recognizing them as foreign and mounting an immune response to destroy the graft.

Clinical Significance:

Defects or dysregulation of CMI can lead to various disorders and diseases, including immunodeficiencies, chronic infections, autoimmune conditions, and impaired antitumor responses. Understanding the mechanisms of CMI is crucial in the development of vaccines, immunotherapies, and diagnostic tools to target specific immune responses and enhance overall immune function.