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The Specific Immune Response Objectives: • Describe the structure and mode of action of T lymphocytes and B lymphocytes, including the significance of cell signalling and the role of memory cells. The Specific Immune Response • This refers to the specific action of lymphocytes T lymphocytes (cell-mediated response) and B lymphocytes (humoral/antibodymediated response) to combat infection by specific pathogens. • However, overall coordination of the immune response also involves the phagocytes, (in particular the macrophages in their role as Antigen Presenting Cells) Cell Mediated Response – T cells • T-killer cells. These T-CELLS attack anything in the body that is recognised as foreign. They may kill the invading organism itself, or they may kill body cells that have been infected with the organism. The cells literally line up, membrane to membrane, then the killer cell punches holes in the other cell’s membrane. It loses cytoplasm and dies. • T-helper cells - release cytokines to stimulate B-cells to divide and to stimulate macrophages for phagocytosis. • T-memory cells – remain in the blood ready to mount the secondary immune response upon reinfection. Antibody Mediated Response – B cells • This involves only antibody chemicals, not the B-cells themselves. • B-plasma cells – manufacture antibodies. • B-memory cells – remain in the blood ready to manufacture the correct antibody quickly upon secondary infection. 1. 2. A pathogen enters your body and multiplies. It has a specific shaped antigen on its cell surface membrane. Your lymphocytes with the complementary antibody may come into contact with this antigen in one of three ways: - By encountering the pathogen itself - By your macrophages engulfing the pathogen, then presenting the antigen on their surface - By the pathogen infecting your body cells, and your body cells then displaying the antigens on their surface. The body cells do this both as a distress signal, and to mark themselves for destruction by T killer cells. 3. When the correct T and B antibodies bind with the pathogenic antigens, this is known as clonal selection. 4. The ‘selected’ lymphocytes will then divide rapidly by mitosis to make many copies of themselves. This is known as clonal expansion or proliferation. 5. The cells now differentiate into particular types of B or T cells. 6. T-cells differentiate into: - T Killer Cells (attack infected host cells) - T Memory Cells (remain in blood) - T Helper Cells (release cytokines to stimulate B-cells to divide and to stimulate phagocytosis) 7. B-cells differentiate into: - Plasma Cells (make antibodies) - B Memory Cells (remain in blood) Types of Cytokines • Cytokines are a group of cell signalling molecules that are involved in communication between the white blood cells of the immune system. • Macrophages release monokines to attract neutrophils by chemotaxis, and to stimulate B cells to differentiate and release antibodies. • T-cells, B-cells and macrophages release interleukins to stimulate proliferation and differentiation of B and T cells. • Many cells release interferon, which inhibits virus replication and stimulates the activity of T Killer cells.