24 Questions
What is the estimated number of different antibody receptors on B cells?
1 x 10^12
What happens when an antigen enters the body?
It selects a specific clone and activates it.
What is the function of antibody-secreting plasma cells?
To synthesise and secrete antibodies.
How long do antibody-secreting plasma cells survive?
For several days.
What is the function of long-lived memory cells?
To respond to antigens at a later time.
What is the primary immune response?
The response of the acquired immune system to a particular antigen for the first time.
What is the characteristic of a clone of B cells?
They have the same antigen specificity.
What is the difference between the primary immune response and the response to a repeated antigenic stimulation?
The response to repeated stimulation is faster and stronger.
Which of the following antibody classes is responsible for immunity to worm infections of the intestinal tract?
IgE
Which of the following antibody classes is present on the surface of B lymphocytes?
IgM and IgD
Which of the following functions is NOT associated with IgG?
Fixation to mast cells and basophils
Which of the following antibody classes can cross the placental barrier from mother to foetus?
IgG
Which of the following antibody classes is the first type of antibody produced after primary antigenic stimulation?
IgM
Which of the following functions is associated with IgA?
Preventing pathogens from entering the body
Which of the following antibody classes is involved in allergic reactions?
IgE
Which of the following functions is associated with IgM?
Triggering the complement system
What is the primary reason for the lag period of 5-10 days immediately after antigen challenge?
Processing of antigen and activation of B cells
What happens to the specific serum antibody level during the primary immune response?
It begins to rise and peaks within several weeks
What is a characteristic of the secondary immune response?
Faster and stronger response
What is the role of memory cells in the secondary immune response?
Providing immunological memory
What is the function of the antigen-binding sites on an antibody molecule?
To bind to the antigen with high specificity
What is the crystallisable fragment (Fc) region of an antibody molecule?
The tail part of the antibody molecule
What is the basis for giving boosters when using some vaccines?
To increase the production of memory cells
What is the result of continuous production of antibodies by long-lived plasma cells?
Antibody levels in the blood remain high for many years
Study Notes
Clonal Selection Theory
- The population of cells from the blast cell, all with the same specificity, is called a clone.
- The foreign antigen selects a lymphocyte with complementary receptors.
- There are approximately 1 x 10^12 different antibody receptors, which means 1 x 10^12 different B cell clones.
Clonal Selection
- There are many lymphocyte populations in the body, each recognizing a single antigen.
- When an antigen enters the body, it selects a specific clone and activates it.
- The small clone proliferates and differentiates to produce a much larger clone of antibody-secreting plasma cells and long-lived memory cells.
- All cells from this large clone are specific for the same antigen.
Antibody Formation & Memory
- Antibody-secreting plasma cells synthesize and secrete antibodies for several days and then die.
- Each plasma cell can synthesize 10 million antibody molecules per hour.
- Antibodies are secreted into the blood and other fluids, binding to specific antigens to prepare them for destruction.
- Long-lived memory cells react with the same antigen if it enters the body again at a later time.
Primary Immune Response
- The response of the acquired immune system the first time it is exposed to a particular antigen.
- Immediately after antigen challenge, there is a lag period of 5-10 days with no observable increase in specific serum antibodies.
- The primary immune response peaks within several weeks and then declines over the next few weeks to months.
Secondary Immune Response
- The response is faster, stronger, and longer-lasting when a person is exposed to the same antigen a second time.
- The immune system was primed to the antigen in the primary response, resulting in increased numbers of specific memory lymphocytes.
- Memory cells provide immunological memory and are responsible for the powerful secondary response.
Antibody Structure
- Antibodies are also called immunoglobulins and are proteins found in blood and other body fluids.
- The molecule has a Y-shaped structure, which can change to a T-shape because of a flexible hinge region.
- The molecule has two 'arms' (antigen-binding fragments, Fab) with high specificity for antigen-binding.
Antibody Classes
- There are five immunoglobulin (Ig) classes: IgD, IgM, IgG, IgA, and IgE.
- Each class of antibody has a different biological function.
- IgM is the first type of antibody produced after primary antigenic stimulation and lasts for weeks to months.
- IgG is the most abundant, persists for months to years after antigenic stimulation, and provides long-term protection.
- IgA is found in mucus covering mucosal surfaces and has a secretory piece.
- IgE is involved in immunity to worm infections of the intestinal tract and allergic reactions.
Biological Properties of Human Immunoglobulins
- IgG binds to antigen, crosses the placenta, and triggers the complement system.
- IgM binds to antigen and triggers the complement system.
- IgA binds to antigen and has a secretory piece.
- IgE binds to antigen and is involved in allergic reactions.
- IgD binds to antigen and is present on the surface of B lymphocytes.
Understanding the concept of clonal selection theory, where a population of cells with the same specificity is formed, and how it relates to the immune system and antibody receptors.
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