The Adaptive Immune System

Question 1

THE ADAPTIVE IMMUNE SYSTEM

3 main components:

Answer 1

• Antigens
• B lymphocytes and antibodies
• T lymphocytes

Question 2

ANTIGEN

Answer 2

• Chemical structure recognised by the adaptive immune system

Question 3

ANTIGEN RECEPTORS

Answer 3

• In the WHOLE population of lymphocyte in your body individual members may differ
• The way they differ is what antigens receptor is on their surface

Question 4

B LYMPHOCYTES

Answer 4

• Source of the antibodies of the adaptive response
• The binding of the antigen-bearing particle will be one of the triggers for that specific B lymphocyte to divide and differentiate
• The B lymphocyte needs other signals, commonly provided by an antigen- specific T lymphocyte
• Activated B lymphocyte differentiates it becomes a plasma cell which secretes antibodies

Question 5

ANTIBODIES

Answer 5

• Variable regions that recognises and binds to the antigen

- The constant region is the same for any particular class of antibody (IgM, IgG 7 or IgE or IgA or IgD)

Question 6

Function of antibodies

Answer 6

• Opsonins to allow binding to WBC including phagocytes
• Immune complexes can activate the complement system
• Immune complexes mediate removal of the antigen from circulation in organs such as the liver
• Neutralisation: Antibody binding to a toxin binding to its receptor on a cell: antibody bound to a bacteria may prevent the bacteria from adhering to a surface ‘

Question 7

THE PRIMARY AND SECONDARY RESPONSES OF THE ADAPTIVE IMMUNE SYSTEM
(PRIMARY)

Answer 7

• Primary response occurs at the first exposure to an antigen
• It can take some 5-7 days for the cells to respond
• The antibody is mainly of the IgM class
• At the end of the primary response most of the active lymphocytes die
• But a small number remain and these survivors: memory cells
• Now there are more of that specific lymphocyte than BEFORE exposure to antigen (Immunological memory)

Question 8

THE PRIMARY AND SECONDARY RESPONSES OF THE ADAPTIVE IMMUNE SYSTEM
(SECONDARY)

Answer 8

• Secondary response occur with exposure to the antigen a second time
• Because of memory cells: the secondary response is stronger
• Other changes occur to the lymphocytes as a result of that first exposure
• The response is faster
• More antibody is produced
• Most of the antibody is IgG which is more effective than IgM

Question 9

T LYMPHOCYTES

Answer 9

• The signal that T lymphocytes need to multiply and differentiate is fragments of antigen on the surface of Antigen Presenting Cells (APC)

Question 10

T LYMPHOCYTE FUNCTION

Answer 10

• The specific T lymphocyte recognizes its specific antigen fragments and the response is once again to multiply and differentiate

Different types of T Lymphocytes

• T helper (CD4) lymphocytes which produce cytokines that regulate the immune response
• T cytotoxic (CD8) lymphocytes that destroy cells infected with intracellular pathogens like viruses
• Regulatory T lymphocytes (CD4 and CD25) and their role is to regulate the activity of other T lymphocytes

Question 11

SUMMARY OF IMMUNITY

Answer 11

• When there is an invasion of the body for foreign cells or particles
• The first line of defence involves barriers like the skin and mucous membranes and expulsion
• If those particles breach the defences or they don’t get expelled immediately there remains the second line of defence
• This second line of defence is what constitutes hat we normally think of as the immune system

There are 2 arm to the immune system

• The INNATE system is rapid and non-specific and is triggered via a range of common signals borne by different invading cells. It incorporates phagocytic cells such as neutrophils and macrophages as well as collections of plasma proteins such as the complement system
• The ADAPTIVE system is initially slower but specific and it is triggered by the unique antigens of the invader
• The antigens may be soluble components (e.g. part of a spider venom) or they may be borne on an invading cell (e.g. a pathogenic bacteria)
• The main components of the adaptive immune response are (i) the antibody producing B lymphocytes and (ii) T lymphocytes (either Helper, Cytotoxic, or regulatory)
• The real strength of the ADAPTIVE immune response is that is improves with repeated exposure and this does not happen with the INNATE response
• The is used clinically in the practice of vaccination