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Higher Human Biology
Unit 4
Immunology & Public Health
KEY AREA 2: Specific Cellular Defences
Higher Human Biology
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
Physiology & Health Learning Intentions
KEY AREA 2 – Specific Cellular Defences
a)Immune Surveillance
b)Clonal Selection Theory
c)T and B Lymphocytes
d)Immunological Memory
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)
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
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)
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.
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
2e) Autoimmunity
Autoimmunity (Immune system regulation failure) is when T Lymphocytes
launch an attack (an immune response) on the body’s own cells (selfantigens) and it is the cause of autoimmune diseases
Examples include:Rheumatoid arthritis
Type 1 Diabetes
MS
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
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
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.
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 Blymphocytes that secrete antibodies into the
lymph and blood where they make their way to the
infected area
2j) Action of Lymphocytes
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
2l) Summary of Specific Immune Response
Immunology & Public Health Questions
Key Area 2 – Specific Cellular Defences
1.
Testing Your Knowledge 1
2.
What you should know
3.
Quick Quiz
Page 326
Q’s 1-4
Page 326
Q1-14