1. IMMUNITY
The Immune System
ALBIO9700/2006JK

2. • Physical, chemical and
cellular defences:
– Epithelia that cover the
airways
– Hydrochloric acid in the
stomach
– Blood clotting
– White blood cells
ALBIO9700/2006JK

3. • Immunity – the protection against
disease provided by the body’s defence or
immune system
• Antigen – any large molecule (e.g.
protein) recognised by the body as foreign
• Antibody – a protein made by the
immune system in response to the
presence of an antigen and targeted
specifically at it
• Immune response – lymphocytes
respond to the presence of a pathogen in
the body by producing antibodies
ALBIO9700/2006JK

4. • Cells of the immune system are
produced in the bone marrow
• 2 groups of these cells involved in
defence:
– Phagocytes (neutrophils and
macrophages)
– Lymphocytes
ALBIO9700/2006JK

5. ALBIO9700/2006JK

6. Phagocytes
• Scavengers produced in bone marrow,
removing any dead cells as well as
invasive microorganisms
• Neutrophils:
– 60% of the white blood cells
– Tissue ‘patrol’
– Released in large numbers from stores
but are short-lived
ALBIO9700/2006JK

7. • Macrophages:
– Larger than neutrophils
– Found in organs (lungs, liver, spleen, kidney
and lymph nodes)
– Leave bone marrow and travel in blood as
monocytes
– Long-lived
– Initiates immune responses (cut pathogens up
to display antigens)
ALBIO9700/2006JK

8. ALBIO9700/2006JK

9. Phagocytosis
ALBIO9700/2006JK

10. ALBIO9700/2006JK

11. Lymphocytes
• Smaller than phagocytes with large nucleus
• 2 types that are produced before birth in the
bone marrow:
– B lymphocytes (B cells)
• Remain in bone marrow until mature
• Spread throughout body (lymph nodes and spleen)
– T lymphocytes (T cells)
• Leaves bone marrow and mature in thymus
• Coordinates the immune response, stimulating B cells to
divide and then secrete antibodies into the blood
• Seek out and kill any of the body’s own cells that are
infected with pathogen
ALBIO9700/2006JK

12. B lymphocytes
• Each B cell makes just one type of
antibody molecule
• Cell divides to give small number of cells
that make the same antibody (clone)
• Antibody remains in plasma membrane
and part of each antibody forms a
protein receptor
ALBIO9700/2006JK

13. ALBIO9700/2006JK

14. ALBIO9700/2006JK

15. • Memory cells:
– Basis of immunological memory
(remain circulating for a long time, often
lasting a lifetime)
– Rapidly divide and develop into plasma
cells and more memory cells upon
reintroduction of antigen
– Infection can be destroyed and removed
before any symptoms develop
– Leads to a faster secondary response
ALBIO9700/2006JK

16. ALBIO9700/2006JK

17. Antibodies
• Globular glycoproteins
• Plasma protein (immunoglobulins)
• Consists of:
– 4 polypeptide chain (2 heavy and 2 light)
– Disulphide bridges
– 2 identical antigen binding sites
– Variable region (specific shape that binds to
just one antigen)
– ‘hinge’ region (flexibility for antibody to bind
around antigen)
ALBIO9700/2006JK

18. ALBIO9700/2006JK

19. ALBIO9700/2006JK

20. T lymphocytes
• Have specific cell surface receptors (T cell
receptors)
• Activated when encounter antigen in contact
with another host cell (e.g. macrophage or
invaded body cell)
• 2 types:
– T helper cells
• Secrete cytokines – stimulate B cells to divide and stimulate
macrophage to carry out phagocytosis more vigorously
– killer T cells (T cytotoxic cells)
• Search invaded body cells, attach themselves and secrete
toxic substances (hydrogen peroxide)
ALBIO9700/2006JK

21. ALBIO9700/2006JK