The cell-mediated response is the part of the specific immune response carried out by T lymphocytes. It acts against body cells that display non-self antigens: cells infected by viruses or by bacteria that live inside cells (such as Mycobacterium tuberculosis), cancer cells and transplanted cells. Antibodies cannot reach pathogens inside cells, so this response is essential.The sequence:
1. Antigen presentation: infected body cells display fragments of the pathogen's antigens on MHC proteins on their cell surface membrane. Macrophages that have engulfed pathogens also present antigens.
2. Selection: T helper cells and T killer cells with receptors complementary to the presented antigen bind to it.
3. Activation and clonal expansion: T helper cells release cytokines, which stimulate the selected T cells to divide by mitosis, forming clones.
4. Differentiation: the clones produce more T helper cells, T killer cells and T memory cells.The cytokines from T helper cells also:
• stimulate macrophages to carry out more phagocytosis
• activate B cells, linking the cell-mediated and humoral responses.The activated T killer cells then find and destroy infected cells displaying the antigen (see the next lesson). T memory cells remain, giving a faster response if the same pathogen returns.The cell-mediated response is important in fighting viral infections such as influenza, in tuberculosis, where the bacteria live inside macrophages, and in the rejection of transplanted organs.
1. Antigen presentation: infected body cells display fragments of the pathogen's antigens on MHC proteins on their cell surface membrane. Macrophages that have engulfed pathogens also present antigens.
2. Selection: T helper cells and T killer cells with receptors complementary to the presented antigen bind to it.
3. Activation and clonal expansion: T helper cells release cytokines, which stimulate the selected T cells to divide by mitosis, forming clones.
4. Differentiation: the clones produce more T helper cells, T killer cells and T memory cells.The cytokines from T helper cells also:
• stimulate macrophages to carry out more phagocytosis
• activate B cells, linking the cell-mediated and humoral responses.The activated T killer cells then find and destroy infected cells displaying the antigen (see the next lesson). T memory cells remain, giving a faster response if the same pathogen returns.The cell-mediated response is important in fighting viral infections such as influenza, in tuberculosis, where the bacteria live inside macrophages, and in the rejection of transplanted organs.