T Lymphocytes & Cell-Mediated Immunity

Role of T lymphocytes is called Cell-Mediated Immunity
T lymphocytes are produced in bone marrow
- They then migrate to the thymus gland in the chest
- They mature in the thymus glands
  - Then they are released into the bloodstream
On the surface membrane of T lymphocytes we find T cell receptor
- which attaches to an antigen
Each unique T lymphocyte has a unique T cell receptor
- Due to this there are millions of unique T lymphocytes
  - This means there will be a T lymphocyte that attaches to every possible antigen
T lymphocytes can only recognise antigens which are on the surface of the other cells.
- Four situations where this happens:
  1. When a cell is infected with a virus
  During a viral infection antigens from virus are attached to the MHC molecules & presented on the surface of the infected cell

2. When a mutation takes place in a normal body cell turning it into cancer cell.

Cancer cells often produce proteins which are not produced by healthy cells.

These abnormal proteins can be attached to MHC and presented on the cell surface

3. Cells or tissues have been transplanted

The antigens on the transplanted cells will not be identical to the antigens on the host cells.

Meaning the host immune system will identify these antigens as non-self/foreign

4. When a macrophage engulfs a pathogen

The pathogen’s antigens are displayed on the macrophage surface