5.3: T-lymphocytes and cell-mediated immunity

Molecules present on the surface of cells which are recognised as non-self and stimulate an immune response

B- mature in the bone marrow. T- mature in the thymus gland.
B-Associated with humeral immunity. T- associated with cell-mediated immunity.

-Phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogens antigens on their own cell-surface membrane
-body cells invaded by a virus present some of the viral antigens on their own cell-surface membrane
- cancer cells present antigens on their cell-surface membrane
- transplanted cells from individuals of the same species have different antigens on their cell surface membrane

1. Pathogens invade body cells or are taken in by phagocytes

2. Phagocytes present antigens from the pathogen on its cell-surface membrane

3. Receptors on a t-helper cell fit exactly into these antigens

4. This attachment activates the T cell to divide rapidly by mitosis and form genetically identical cells

5. The cloned T cells
   - develop into memory cells that allow a rapid response upon infection by the pathogen again
   - stimulate phagocytes to engulf pathogens by phagocytosis
   - stimulate b cells to divide and secrete their antibody
   - activate cytotoxic t-cells

Produced a protein called perforin that makes holes in the cell-surface membrane
These holes mean that the cell-surface membrane becomes freely permeable to all substances and the cells die as a result