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Flashcards in The Adaptive Immune System Deck (11)
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1

THE ADAPTIVE IMMUNE SYSTEM
3 main components:

- Antigens
- B lymphocytes and antibodies
- T lymphocytes

2

ANTIGEN

- Chemical structure recognised by the adaptive immune system

3

ANTIGEN RECEPTORS

- 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

4

B LYMPHOCYTES

- 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

5

ANTIBODIES

- 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)

6

Function of antibodies

- 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 ‘

7

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

- 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)

8

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

- 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

9

T LYMPHOCYTES

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

10

T LYMPHOCYTE FUNCTION

- 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

11

SUMMARY OF IMMUNITY

- 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