Clonal Selection: Videos & Practice Problems

Clonal selection is a vital process in the adaptive immune system, where specific B and T cells are activated in response to a particular antigen. Each B cell has identical B cell receptors (BCRs) that recognize different antigens. Upon infection, only the B cell with the matching BCR proliferates, creating clones that can effectively combat the antigen. These clones differentiate into plasma cells, which secrete antibodies, or memory B cells for faster responses to future infections. This selective proliferation ensures a targeted immune response, enhancing overall immunity.

Clonal Selection

The clonal selection theory is a fundamental concept in immunology that explains how the adaptive immune system responds to specific antigens. Each B and T cell in the body possesses unique B cell receptors (BCRs) or T cell receptors (TCRs) that allow them to recognize and respond to particular antigens. When an infection occurs, the immune system activates only those B and T cells that can specifically bind to the invading antigen, leading to their proliferation and differentiation.

Upon encountering a specific antigen, such as a pathogen, the clonal selection theory posits that only the B and T cells with receptors that match the antigen will be selected for activation. This process ensures that a targeted immune response is generated. For instance, in a mixed population of B cells, only the B cell that can bind to the antigen will undergo activation and begin to proliferate, creating a large number of identical clones. This proliferation is crucial for mounting an effective immune response against the specific pathogen.

After activation, the selected B cells differentiate into two main types: plasma cells and memory B cells. Plasma cells are responsible for producing antibodies that specifically target the antigen, aiding in its elimination from the body. Memory B cells, on the other hand, remain in the body to provide a faster and more robust response if the same antigen is encountered again in the future. This differentiation is vital for long-term immunity and the ability to respond quickly to subsequent infections.

In summary, the clonal selection theory illustrates how the immune system efficiently narrows down a diverse population of B and T cells to those that can specifically combat an infection, ensuring a focused and effective immune response. This mechanism highlights the importance of specificity in the adaptive immune system, allowing for both immediate and long-lasting protection against pathogens.

Which of the following statements is FALSE?

• A. Each B cell has BCRs that bind to a single antigen.
• B. The cell type that secretes antibodies is called a plasma cell.
• C. A BCR allows naive B cells to detect an antigen.
• D. All naive B cells that are close in proximity to an antigen begin to differentiate.

Answer: (D)

Clonal selection:

• A. Implies that each individual lymphocyte produces a single antibody.
• B. Describes how the adaptive immune system can produce millions of different antibodies.
• C. Depends on an antibody recognizing a specific epitope.
• D. Is based on random naive B cells proliferating and differentiating.

Answer: (C)

The clonal selection theory states that:

• A. Self-reacting T cells are destroyed in the bone marrow.
• B. B cells will only proliferate during an infection if their BCRs successfully bind to the pathogen.
• C. Antibody structure changes as it encounters an antigen for higher specificity binding.
• D. Each T cell produces many different types of antibodies.

Answer: (B)

Which of the following is NOT an organ where clonal selection occurs?

• A. Spleen.
• B. Lymph nodes.
• C. Bone marrow.
• D. Mucosa associated lymphoid tissue.

Answer: (C)

All of the following are postulates of the clonal selection theory EXCEPT:

• A. Each B lymphocyte bears a single type of receptor with a unique specificity.
• B. BCR occupation is required for cell activation.
• C. Differentiated cells derived from an activated B lymphocyte bear receptors of similar specificity as the parent cell.
• D. B lymphocytes bearing receptors for self-molecules are destroyed at an early stage.
• E. All are postulates of the clonal selection theory.

Answer: (D)

Here’s what students ask on this topic:

What is clonal selection in the immune system?

Clonal selection is a fundamental process in the adaptive immune system where specific B and T cells are activated in response to a particular antigen. Each B cell has identical B cell receptors (BCRs) that recognize different antigens. Upon infection, only the B cell with the matching BCR proliferates, creating clones that can effectively combat the antigen. These clones differentiate into plasma cells, which secrete antibodies, or memory B cells for faster responses to future infections. This selective proliferation ensures a targeted immune response, enhancing overall immunity.

How does clonal selection theory explain the immune response to specific antigens?

Clonal selection theory explains that upon encountering a specific antigen, only the B and T cells with receptors (BCRs and TCRs) that match the antigen are selected to proliferate. These selected cells then multiply, creating identical clones that can effectively target the antigen. The clones differentiate into plasma cells, which produce antibodies, or memory cells, which provide a faster response if the antigen is encountered again. This process ensures that the immune system mounts a precise and efficient response to the specific antigen.

What roles do plasma cells and memory B cells play in clonal selection?

In clonal selection, plasma cells and memory B cells play crucial roles. Plasma cells are differentiated B cells that secrete large amounts of antibodies specific to the antigen, helping to neutralize and eliminate the pathogen. Memory B cells, on the other hand, are long-lived cells that remain in the body after the initial infection. They provide a rapid and robust response if the same antigen is encountered again, ensuring quicker and more effective immunity during subsequent infections.

Why is clonal selection important for adaptive immunity?

Clonal selection is vital for adaptive immunity because it ensures a highly specific and efficient immune response. By selecting only the B and T cells that recognize a particular antigen, the immune system can focus its resources on combating the specific pathogen. This targeted response not only helps in effectively eliminating the infection but also creates memory cells that provide long-term immunity. This specificity and memory are key features that distinguish adaptive immunity from the innate immune response.

How do B cell receptors (BCRs) and T cell receptors (TCRs) function in clonal selection?

B cell receptors (BCRs) and T cell receptors (TCRs) are crucial for clonal selection. BCRs are membrane-bound antibodies on B cells that bind to specific antigens. When a BCR binds its matching antigen, the B cell is activated to proliferate and differentiate into plasma cells and memory B cells. Similarly, TCRs on T cells recognize antigens presented by other cells. Upon binding to their specific antigen, T cells are activated to proliferate and differentiate into effector T cells and memory T cells. This receptor-antigen interaction is the basis for the selective activation and proliferation of specific immune cells.