4.1.7 The T Lymphocyte Response

Question 1

T Lymphocytes

Answer 1

Lymphocytes and antibodies provide the 3rd line of defence against pathogens
- unlike the 1st and 2nd line of defence, the 3rd line is specific
- specific immune responses are slower but more effective than no-specific immune responses
Lymphocytes are:
- a type of white blood cell
- smaller than phagocytes
- have a larger nucleus that fills most of the cell
- produced in the bone marrow before birth
- travel around the body in the blood
There are 2 the types of these lymphocytes with different modes of action
- one of them is T-lymphocytes (T Cells)
- these mature in the thymus gland

Question 2

Maturation of T-Lymphocytes

Answer 2

Immature T-Lymphocytes originate in the bone marrow
They move to the thymus gland in the chest, which is where they mature
During the process of maturation, T Cells gain specific surface receptors called T cell receptors (TCRs)
- these receptors have a similar structure to antibodies and are each complementary to a different antigen
- a small number of T cells have the same TCRs, these are genetically identical cells and are called clones
- T cells within each clone differentiate into different types of T cell: T helper cells, T killer cells and T regulator cells
There is a very large number of different T cells with different TCRs
- this variation allows the T cells to recognise a wide range of foreign antigens
- foreign antigens can be found on the surface of microorganisms, their cell products and toxins
The matured T cells remain inactive until they encounter their specific antigen