Acquired Immunity Flashcards
Definition of acquired immunity
If the 1st line of defence is breached, acquired immunity is activated to produce a specific reaction against the infectious/provoking stimulus
- Requires T and B cells.
- Specific
- Slow on first exposure
- Development of memory -> subsequent exposure triggers rapid response
2 Components:
- Humoral and Cellular
Humoral Immunity
Antibody production by b lymphocytes
B cells are usually dormant in lymphoid tissue
After exposure to an antigen, there is an interval of ~2weeks before antibodies can be found in blood.
The invading antigen is first localised and phagocytose by Macs that present it to adjacent B cells
Antigen also activates helper T-cells
B cells then proliferate and turn into plasma cells in the lymph gland.
Plasma cells release antibodies into the lymph ->blood.
Cellular immunity
T- lymphocytes
B Cell activation
- T-cell dependent activation.
- B Cell express MHC class 2 antigens on their surface.
- Helper T-Cell (CD4) binds B-Cell surface and activation occurs - T-Cell independent activation
- Antigen specific.
- Only b cells whose receptors recognize the epitope will be activated.
Therefore direct recognition of antigen can activate
B Cell Function
- Production of antibody against specific antigens w the aid of T-Cells
- Presentation of Antigen to stimulate t-cell activation.
Once activated become plasma cells
Plasma cells:
- produce antibodies that bind the antigen and either activate compliment to destroy the antigen, or opsonise it to facilitate phagocytosis by Macs and nuts
Define Antigen
Antigen is a substance that is capable of stimulating the immune system of the host to produce a specific response to it.
Usually located on cell wall of pathogen.
Define Immunoglobulins
IGs are serum globulins w immune functions.
All antibodies are IG, but not all IGs have antigen binding functions.
Structure:
- 2 identical light chains and heavy chains linked into a four chain structure.
- Looks like a Y
- Each light and heavy chain has a constant and a variable portion.
- Constant portion= mediates effector functions eg complement activation. Fc Fragment.
- Variable portion = antigen binding site.
IgG
Most abundant, 75% of total serum IG.
High antigen affinity
Secondary immune response
Only IG that crosses the placenta to the foetus
Activate classical pathway of complement system.
IgM
Primary immune response
First line defence mechanism
Potent activator of complement via classical pathway
Blood Group antibodies are IgM
IgA
Found in mucus membrane secretions
Present in saliva, tears, breast milk, bronchial fluid, GI secretions
Protects mucosa against microbial invasion and growth
Activates the alternative pathway of the complement cascade
Is an opsonin
Reacts w receptors on Macs and nuts
IgE
Low concentrations in serum
most bound to mast cells
Increase in parasitic infections, atopy, immediate hypersensitivity reactions
Antigen binding to IgE = mast cell activation and degranulation.
IgD
Cell surface receptor on B cells and may be involved in B-cell activation
T cells
Arise from the thymus
Have an antigen specific receptor called TCR (T-cell receptor)
80% of circulating lymphocytes.
Processed T-Cells leave the thymus and spread to lymphoid tissue throughout body.
2 main types
- Helper T cells
- Cytotoxic T cells
Helper T cells
2/3 of T cells
Distinguished by presence of surface glycoprotein CD4.
Have the ability to recognise antigen only when expressed w MHC Class 3 molecules on APC.
CD4 binds to MHC Class 2 on APCs.
Functions:
- release cytokines (IL 4,5,6,10 and IFNy)
- Activate macrophages
- Stimulate b cells to form plasma cells and antibodies.
Divided into T Helper 1 and T Helper 2 cells.
