Cellular Immunity

Subject – Science and Tech

Context – ‘AstraZeneca/Covishield kept death rate low in UK’

Concept –

Cell-mediated immunity is an immune response that does not involve antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.
Cellular immunity protects the body through:
- T-cell mediated immunity or T-cell immunity: activating antigen-specific cytotoxic T cells that are able to induce apoptosis in body cells displaying epitopes of foreign antigen on their surface, such as virus-infected cells, cells with intracellular bacteria, and cancer cells displaying tumor antigens;
- Macrophage and natural killer cell action: enabling the destruction of pathogens via recognition and secretion of cytotoxic granules (for natural killer cells) and phagocytosis (for macrophages);
- Stimulating cells to secrete a variety of cytokines that influence the function of other cells involved in adaptive immune responses and innate immune responses.

Adaptive Immunity

There are two main mechanisms of immunity within the adaptive immune system – humoral and cellular.

Humoral immunity is also called antibody-mediated immunity. With assistance from helper T cells, B cells will differentiate into plasma B cells that can produce antibodies against a specific antigen. The humoral immune system deals with antigens from pathogens that are freely circulating, or outside the infected cells. Antibodies produced by the B cells will bind to antigens, neutralizing them, or causing lysis (dissolution or destruction of cells by a lysin) or phagocytosis.
Cellular immunity occurs inside infected cells and is mediated by T lymphocytes. The pathogen’s antigens are expressed on the cell surface or on an antigen-presenting cell. Helper T cells release cytokines that help activated T cells bind to the infected cells’ MHC-antigen complex and differentiate the T cell into a cytotoxic T cell. The infected cell then undergoes lysis.