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because the transferred antibodies eventually degrade and are not replenished by the recipient's immune system. Both active and passive immunity are valuable components of the body's defense against infections and are utilized in different scenarios, such as natural infections, vaccinations, and medical interventions. Cell-mediated immunity is a vital component of the immune response that involves the action of T-cells . When the body is exposed to an antigen (a foreign substance, such as a virus or bacterium), lymphoid tissues release large numbers of activated T-cells into the lymphatic system. These T-cells play various roles in coordinating and executing the immune response . Here are the three main types of T-cells involved in cell-mediated defenses: Helper T cells (CD4+ T cells) : ●​ Helper T cells play a central role in regulating and enhancing the immune response . When they encounter an antigen-presenting cell (such as a macrophage) displaying the antigen, they become activated. ●​ Once activated, helper T cells release signaling molecules called cytokines . These cytokines stimulate other immune cells, including B-cells (for antibody production) and cytotoxic T cells, to become more efficient in combating the infection. ●​ Helper T cells are crucial in coordinating both cell-mediated and antibody-mediated immune responses . Without them, the immune system's ability to eliminate pathogens would be significantly impaired. Cytotoxic T cells (CD8+ T cells) : ●​ Cytotoxic T cells are the " effector " cells of the cell-mediated immune response. They directly attack and destroy infected cells, cancer cells, or cells presenting foreign antigens. ●​ When cytotoxic T cells recognize an infected or abnormal cell displaying the antigen, they release cytotoxic granules containing perforin and granzymes . Perforin creates pores in the target cell's membrane, allowing granzymes to enter and trigger apoptosis (cell death) of the infected cell. ●​ Cytotoxic T cells are particularly effective in combating intracellular pathogens, such as viruses, as they can eliminate infected cells before the pathogen replicates and spreads to other cells. Suppressor T cells (Regulatory T cells) : ●​ Suppressor T cells play a crucial role in regulating the immune response to prevent excessive or prolonged reactions that could harm healthy tissues. ●​ They suppress the functions of helper T cells and cytotoxic T cells to avoid excessive inflammation and tissue damage. This balance is essential for preventing autoimmune reactions where the immune system mistakenly attacks the body's cells.

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