Immunity to Infection: Adaptive Immunity and Antibodies Flashcards
Dr. Idowu
What is adaptive immunity?
It is the body’s second-line of defense provides specific response to an antigen and confers long-lasting protective immunity and immunologic memory.
What is an antibody?
An antibody is a Y-shaped protein that is produced by the proliferation and differentiation of B lymphocytes into plasma cells, which can specifically bind to the corresponding antigen.
Antibodies are only found in body fluids of vertebrates and on the B-cell surface.
True or False
True.
After antibodies bind to different antigens, different responses are produced, so antibodies are given different names, such as:
- hemolysin
- lectin
- precipitin
- antitoxin
- lysozyme
Describe the structure of an antibody.
An antibody is a globular blood protein macromolecule weighing about 150 kDa.
The monomer of an antibody is a Y-shaped molecule with a symmetrical structure of four polypeptide chains, of which two chains are longer heavy chains (H chains) with a relatively high molecular weight, and two chains are shorter light chains (L chains) with a relatively low molecular weight.
Activated B cells can differentiate into two kinds of cells with different functions. They are:
i. Plasma cells: produce antibodies
ii. Memory cells memorise the antigens contacted
Antibodies in a fetus and new born are provided by the mother as a kind of passive immunity.
True or False
True
What is the main function of the antibody?
to combine with antigens (both foreign and self) to effectively remove foreign bodies, neutralise the toxins released by them, or to remove some autoantigens, maintaining the normal balance of the body
Mention three types of antibodies that cause pathological damage to the body, leading to autoimmune disease.
i. Anti-nuclear antibodies
ii. Anti-double-stranded-DNA antibodies
iii. Anti-thyroglobulin antibodies
Highlight the biological activity of the antibody.
- They bind specific antigens: antibodies by to antigens by relying on the specific binding sites on the molecule.
- They activate complement: after binding to the antigen, the complement system is activated using the exposed complement-binding sites
- They bind cells: they bind to different cells involved in immune response
- IgG can pass from mother to fetus, providing passive immunity. IgA provides local mucosal immune response.
- Antigenicity: they also have the ability to stimulate the body to produce an immune response.
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Antibody resistance to physical and chemical factors is different from general globulins:
i. they are thermolabile (destroyed at 60-70 degree-celcius),
ii. susceptible to destruction by enzymes and substances that cause protein coagulation.
iii. precipitated by neutral salts e.g. ammonium sulfate or sodium sulfate
Highlight the Production Law of Natural Antibodies.
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Production of antibodies in primary response: When the antigen enters the body for the first time, antibodies are produced after a certain incubation period, but very little is produced; it is also maintained in vivo for a shorter time.
Its main features are as follows:
i. the latency of primary immune response is long
ii. the concentration of antibody produced is low
iii. and the antibody–antigen affinity is also low, mainly IgM.
iv. Short in vivo retention time. -
Production of antibodies in secondary response: Upon exposure to the same antigen, some of the original antibodies initially bind to the antigen, causing a reduction in the original amount of the antibody.
Subsequently, there is a rapid increase to several times more than the primary response, and its in vivo retention time is also longer.
Its main features are as follows:
i. the latency is usually as short as 1–3 days
ii. high antibody concentration
iii. and the antibody-antigen affinity is high, mainly IgG.
iv. Longer in vivo retention time -
Production of antibodies in anamnesis reaction (memory): The antibodies produced by the antigens gradually disappear after a certain period. At this point, if the antigen is contacted again, there’ll be a rapid increase in the antibody.
If the antigen stimulating the body again is the same as that at the first time, it is known as the specific anamnesis reaction; if it is different from that in the primary response, it is known as a nonspecific anamnesis reaction.
The increase of antibodies caused by a nonspecific anamnesis reaction is temporary and will decline rapidly in a short time.
Classify antibodies according to physical and chemical properties and biological functions.
i. IgG
ii. IgA
iii. IgM
iv. IgE
v. IgD
GAMED
Briefly describe IgG.
- Accounts for 75% total serum immunoglobin, with normal values of 9.5-12.5mg/ml.
- 40-50% of IgG is in the serum, while the rest is in the tissues.
- Molecular weight is 150 kDa
- It’s mainly a monomer and has 4 subtypes IgG1, IgG2, IgG3 and IgG4
- It’s the only antibody that can cross the placenta and protects the fetus.
- It is also passed from breast milk to the newborn
- Most antibacterial, antiviral and antitoxin antibodies produced by antigens are IgG
- Many antibodies such as LE factor and anti-thyroglobulin antibodies are also IgG
- Synthesis starts from 3 months of age, peaking at age 3-5 years and declining at age 40.
- Most of IgG passed to fetus depletes at 6 months after birth.
Briefly describe IgA.
- Second highest immunoglobin amount after IgG (10-20%)
- Divided into two types: serum IgA and secretory IgA
- Serum IgA does not show any important immune function in serum’
- Secretory IgA is present in saliva, lacrimal fluid amd other exocrine fluids
- Present in mucosal surfaces and produced by mucosa-associated lymphoid tissues
- It’s an important factor for mucosal immunity
- They cannot pass the placenta
- They can be passed to infant via breast milk.
- Synthesised 4-6 months after birth, peaking at age 4-12 years
Briefly describe IgM.
- 5-10% of total serum immunoglobin
- Natural blood group antibody
- Cannot cross the placenta
- It is the first antibody synthesised in individual development
- It is the first antibody secreted during immune response
- Initiates complement cascade and causes agglutination of intruders to be engulfed by macrophages
- Of clinical diagnostic value for some infectious diseases
- Peaks at age 1 year