Third Line of Defence
The Third Level of defence involves cells and chemicals which target specific antigens and act against them.
Cell Mediated Response
T Cells
Types of T Cells
Cell Mediated Response
- Cell mediated immunity involves T cells acting directly against a foreign organism or secrete lymphokines which will initiate the bodies humoural response.
- If an antigen invades an organism, macrophages engulf the antigen, break it down and present the antigen on its surface as an MHC marker. the MHC marker is presented to lymphocytes which includes T Cells. It a T Cell has the complimentary receptor for that antigen, then the T Cell becomes stimulated directly acting the antigen. Some T Memory Cells for that antigen remain in the lymph nodes.
T Cells
- T cells are lymphocytes which are a type of white blood cell. They mature in the gland known as the Thymus located in the chest.
- All T Cells have different receptors for a complimentary MHC marker for that antigen.
Types of T Cells
- Cytotoxic T Cells
- T Helper Cells
- Suppressor T Cells
- T Memory Cells
Humoural Response (Antibody Mediated Response)
B Cells
Types of B Cells
Stages of Humoural Response
1. A substance or cell with a foreign antigen invades the body
2. Macrophages engulf the antigen, display it on their surface and travel to the lymph nodes.
3. The antigen is presented to T helper cells which presents the antigen to B cells.
4. B cells reproduce by mitosis forming a clone of identical B cells, most become plasma cells that produce antibodies and some become memory cells which remain in the lymph node.
- If a T Cell presents and antigen to B Cells then the humoural response is able occur.
- If an antigen invades the body, macrophages engulf the antigen and displayed on its surface. These antigens are then presented to Cells which then present the antigen to B Cells. The B Cell with the complimentary receptor begins to replicate rapidly into B Plasma Cells and B Memory Cells. The B Plasma Cells attack the antigen while B Memory Cells stay in the lymph nodes.
B Cells
- They are formed in bone marrow and migrate directly to the lymph nodes. They form plasma and memory cells, each with its surface covered with thousands of identical copies of a receptor for an antigen.
Types of B Cells
- B Plasma Cells
- B Memory Cells
Stages of Humoural Response
1. A substance or cell with a foreign antigen invades the body
2. Macrophages engulf the antigen, display it on their surface and travel to the lymph nodes.
3. The antigen is presented to T helper cells which presents the antigen to B cells.
4. B cells reproduce by mitosis forming a clone of identical B cells, most become plasma cells that produce antibodies and some become memory cells which remain in the lymph node.