3.2.4 - T Cells & Cell-Mediated Immunity
Tuesday 9th January ‘23
Phagocytosis response is non-specific and it is not enough to cope with large numbers of pathogens e.g the flu virus.
Specific responses are slower in action that non-specific responses, but they offer longer term immunity. The specific immune response depends on a type of white blood cell called lymphocytes (these already exist, 10million types so high probability one will have a protein complementary to antigen on pathogen).
B Cells - mature in bone marrow, associated with humoral response.
T Cells - mature in thymus gland, associated woth cell-mediated immunity.
Cytotoxic T cells
Helper T cells
Memory T cells
How can T cells distinguish between self and non-self cells?
Phagocytes that have engulfed and hydrolysed a pathogen will present some of the antibodies on its cell membrane.
Body cells invaded by a virus will present some of the viral antigens on their cell membrane
Transplanted cells from individuals of the same species have different antigens on their cell membrane (non-self).
Cancer cells are different to normal body cells and present different antigens on their surface.
When a specific T cell responds, it is stimulated to divide to build up the numbers of that type of cell, to a level where it will be effective in destroying the infection.
T cells will only respond to antigens on surface membrane of cells.
How does the T cell response happen?
Pathogens invade body cells, or are engulfed by phagocytes.
The phagocyte places antigens from the pathogen on its cell-surface membrane.
Receptors on a specific helper T cell fit exactly onto these antigens.
This attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells.
What do cloned T cells do?
Develop into memory cells that enable a rapid response to future infections by the same pathogen.
Stimulate phagocytes to engulf pathogens by phagocytosis.
Stimulates B cells to divide and secrete the antibody.
Activate cytotoxic T cells.
Kill abnormal cells and body cells infected by pathogens by producing a perforin protein that makes holes in the cell-surface membrane.
These holes mean the cell membrane becomes freely permeable to all substances and the cell dies as a result.
Who do they like killing?
Viruses - these replicate inside cells. The sacrifice of body cels prevents viruses from being able to replicate, and thus infecting more cells.