1. Unit 4 Immunology & Public Health
Higher Human Biology
Unit 4
Immunology & Public Health
KEY AREA 2: Specific Cellular Defences

2. Higher Human Biology Key Area 1 – Non-specific Defences
We are going to build on the knowledge and skills that you developed during N5 and will learn about the following Immunology & Public Health key areas : -
Key Area 1 – Non-specific Defences
Key Area 2 – Specific Cellular Defences
Key Area 3 – Transmission and Control of Infectious Diseases
Key Area 4 – Active Immunisation and Vaccination and the Evasion of Specific Immune Responses by Pathogens

3. Physiology & Health Learning Intentions
KEY AREA 2 – Specific Cellular Defences
Immune Surveillance
Clonal Selection Theory
T and B Lymphocytes
Immunological Memory

4. 2a) Specific Cellular Defences
Lymphocytes carry out a specific immune response
Lymphocytes are made from stem cells in bone marrow
Some lymphocytes pass to the thymus gland and develop into T Lymphocytes (T cells)
Lymphocytes that remain and mature in the bone marrow develop into B Lymphocytes (B cells)

5. 2b) Immune surveillance
Immune surveillance is when a range of white blood cells constantly move around the circulatory system and continuously monitor the state of the tissues
If tissues become damaged or invaded then white blood cells release cytokines into the bloodstream causing an increase in blood flow resulting in white blood cells (phagocytes and T- lymphocytes) accumulating at the site of infection or tissue damage

6. 2c) Clonal Selection Theory
Any foreign molecule that is recognised by a Lymphocyte is called an antigen. All cells have antigenic markers on their surface made of protein
‘Foreign’ antigenic markers (proteins) on the outer surface of Viruses and bacteria; bacterial toxins and molecules on the surfaces of; transplanted cells (immuno-surpressor drugs) and cancer cells, can all act as antigens.
Each Lymphocyte has on the surface of its cell membrane, several copies of a single type of antigen receptor as a result of previous exposure (memory cells)

7. Lymphocytes have a single type of membrane receptor specific for only one type of antigen
When a specific lymphocyte is activated by a specific antigen, it is said to have been “selected” by the antigen.
This antigen binding leads to repeated lymphocyte division forming a clonal population of identical lymphocytes – this process is called clonal selection.

8. 2d) T & B Lymphocytes Recognition of self and non-self
Each person’s body cells are unique to that person because they contain a combination of cell surface proteins that are specific to that person. This is the person’s “antigen signature”
The “antigen signature” is critical to ensure that a person’s own lymphocytes do not try to destroy their own body cells surface proteins. This normally does not happen because during maturation of B cells and T cells, any lymphocytes bearing an antigen receptor that fits a body cell surface protein is weeded out
T Lymphocytes have specific surface proteins that allow them to distinguish between the surface molecules of the body’s own cells and cells with foreign molecules on their surface

9. 2e) Autoimmunity
Autoimmunity (Immune system regulation failure) is when T Lymphocytes launch an attack (an immune response) on the body’s own cells (self-antigens) and it is the cause of autoimmune diseases
Examples include:-
Rheumatoid arthritis
Type 1 Diabetes MS

10. 2f) Allergy
Sometimes the immune system over-reacts by hypersensitive B Lymphocytes responding to harmless substances (e.g. pollen, dust, feathers, penicillin)
This is called an allergic reaction
Read page 319 of your Textbook and the case studies on:-
Hay Fever
Anaphylactic Shock
Allergic Asthma

11. 2g) Action of Lymphocytes
There are 2 groups of T lymphocytes
Group 1 (Helper T cells)
These cells secrete cytokines to activate Phagoctyes (non – specific), Cytotoxic T cells and B (lymphocyte)cells
Group 2 (Cytotoxic T cells)
These cells destroy infected cells by apoptosis

12. 2h) Antigen-presenting cell
When pathogens infect tissue, some phagocytes capture the pathogen and display fragments of its antigens on their surface.
These antigen presenting cells activate the production of a clone of Helper T cell Lymphocytes that move to the site of infection secreting cytokines which stimulate s Cytotoxic T cells and B cells.

13. 2i) B Lymphocytes
Each B lymphocyte clone produces a specific antibody molecule that will recognise a specific antigen surface molecule on a pathogen or toxin
Antigen-antibody complexes may inactivate a pathogen or toxin or render it more susceptible to phagocytosis
In other cases, antigen-antibody complex stimulated a response which results in cell lysis
B lymphocytes activated by antigen presenting cells and T lymphocytes produce a clone of B-lymphocytes that secrete antibodies into the lymph and blood where they make their way to the infected area

14. 2j) Action of Lymphocytes

15. 2k) Immunological Memory
Some T- and B-lymphocytes produced in response to antigens by clonal selection survive long-term as memory cells.
A secondary exposure to the same antigen rapidly gives rise to a new clone of lymphocytes producing a rapid and greater immunological response

16. 2l) Summary of Specific Immune Response

17. Immunology & Public Health Questions
Key Area 2 – Specific Cellular Defences
1. Testing Your Knowledge 1 Page Q’s 1-4
2. What you should know Page 326 Q1-14
3. Quick Quiz