Block 9 Immunogentics Dr Sands

The 12/23 rule refers to the requirement for recombination between two different RSS (recombination signal sequence) elements during V(D)J recombination. According to this rule, a RSS heptamer/nonamer with a 12 bp spacer will only recombine with a RSS heptamer/nonamer with a 23 bp spacer. This rule ensures the proper joining of gene segments during the process of generating diverse antigen receptor genes in lymphocytes.

The hypervariable regions of H and L chains form the antibody-binding site. These regions are highly variable and contain amino acid sequences that are specific to each antibody. The variability in these regions allows antibodies to recognize and bind to a wide range of antigens. The constant regions of H and L chains, on the other hand, are relatively conserved and are responsible for the effector functions of antibodies, such as binding to immune cells and activating the immune response. Therefore, it is the hypervariable regions of both H and L chains that play a crucial role in antibody binding.

When a B-cell undergoes immunoglobulin class switching, the variable region of the heavy chain remains the same, but its constant region changes. This process allows B-cells to change the class of antibodies they produce without altering the specificity of the antigen-binding site. The variable region contains the antigen-binding site, while the constant region determines the effector functions of the antibody, such as binding to Fc receptors or activating complement. Therefore, during class switching, the B-cell retains the same antigen-binding specificity but gains new effector functions.

During the maturation of a B lymphocyte, the first immunoglobulin heavy chain synthesized is the Mu chain. This is because the Mu chain is the first heavy chain to be produced during B cell development. It is initially expressed on the cell surface as a component of the IgM antibody, which is the first immunoglobulin isotype produced by immature B cells. As B cells mature, they undergo class switching and can produce other heavy chains such as gamma, epsilon, and alpha. However, the Mu chain is the initial heavy chain synthesized during B cell maturation.

When a B-cell undergoes immunoglobulin class switching, the variable region of the heavy chain remains the same but its constant region changes. This means that the part of the antibody that recognizes and binds to specific antigens remains unchanged, while the part that determines the antibody's function and location within the body is altered. This allows the B-cell to produce antibodies with different effector functions without changing its antigen specificity.

The correct answer is "involve rearrangement of heavy-chain gene segments." During the earliest stages of B-cell differentiation, the heavy-chain gene segments undergo rearrangement. This process is crucial for the production of functional B-cell receptors. The rearrangement of heavy-chain gene segments allows for the generation of a diverse repertoire of B-cell receptors, which is essential for the immune system to recognize a wide range of antigens.

The correct answer is a rearrangement of a heavy-chain gene on only one chromosome in a lymphocyte. This is because allelic exclusion refers to the phenomenon where only one form of a gene is expressed, despite the presence of two allelic forms. In the case of Gm allotypes, heterozygous individuals have two allelic forms of IgG in their serum, but individual lymphocytes only produce one form. This suggests that there is a rearrangement of the heavy-chain gene on only one chromosome in the lymphocyte, leading to the expression of only one form of the gene.

After binding to its specific antigen, a B lymphocyte may switch its Immunoglobulin heavy-chain class. This is because B lymphocytes have the ability to undergo class switching, which is a process that allows them to change the type of immunoglobulin heavy chain they produce. This switch in heavy-chain class results in the production of different types of antibodies with varying effector functions. This process is important for the immune system to generate a diverse range of antibodies that can effectively target different types of pathogens.

P- and N-nucleotides are added to D-J gene junctions before a B cell is exposed to antigen. This statement is true because during the process of V(D)J recombination, P- and N-nucleotides are added to the junctions between the D and J gene segments. This process occurs before a B cell is exposed to antigen, as it is part of the early stages of B cell development in the bone marrow. Somatic hypermutation, isotype switching, and V-D-J recombination events, on the other hand, occur after a B cell is exposed to antigen and undergoes activation and differentiation.

Inheritance of multiple C-region genes does not contribute to the generation of diversity of B-cell antigen receptors. The C-region genes code for the constant region of the antibody molecule, which remains the same regardless of the specific antigen being recognized. The diversity of B-cell antigen receptors is primarily generated through the random assortment of L and H chains, the multiple V genes in the germ line, and the imprecise recombination of V and J or V, D, and J segments. Additionally, somatic mutation also plays a role in generating diversity by introducing random changes in the antibody genes during B-cell maturation.

During the maturation of lymphocytes, the hypervariable region of an antibody light chain is generated through the addition of nucleotides between LV and J segments. This process, known as V(D)J recombination, involves the rearrangement of gene segments to create a diverse repertoire of antibodies. The addition of nucleotides between LV and J segments introduces variability in the amino acid sequence of the hypervariable region, allowing antibodies to recognize a wide range of antigens. This mechanism is crucial for the adaptive immune system's ability to recognize and respond to a diverse array of pathogens.

Isotype switching of immunoglobulin classes by B cells involves successive insertion of a single VH gene adjacent to different CH genes. This means that B cells can change the type of antibody they produce by replacing the constant region of the antibody while keeping the variable region the same. This allows B cells to switch from producing one class of antibody to another, such as from IgM to IgG or IgA. This process is important for generating a diverse immune response and adapting to different types of pathogens.

The greater hypervariability of the CDR3 region compared to the CDR1 region of immunoglobulin heavy chains can be partly attributed to the enzyme terminal deoxyribonucleotidyl transferase. This enzyme is responsible for adding non-template nucleotides during the process of V(D)J recombination, which is the mechanism by which the gene segments encoding the variable regions of immunoglobulins are rearranged. These non-template nucleotide additions introduce additional diversity in the CDR3 region, contributing to the overall hypervariability of immunoglobulin heavy chains.

Alternative polyA site usage refers to the phenomenon where different polyadenylation sites are used during mRNA processing, resulting in the generation of multiple mRNA isoforms from a single gene. In the case of B cells, alternative polyA site usage allows for the expression of cell-surface IgM of the same specificity as the IgM produced for secretion. This is because the alternative polyA site usage leads to the production of different mRNA isoforms that are translated into different protein isoforms, with some being targeted for secretion and others being expressed on the cell surface.

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The correct answer is alternative splicing of a primary RNA transcript. This process allows for the generation of different mRNA isoforms from a single gene, leading to the production of different protein variants. In the case of cells expressing cell-surface IgM, alternative splicing of the primary RNA transcript allows for the production of membrane-bound IgM, which has the same specificity as the IgM secreted by the cell. This enables the cell to display IgM on its surface while also producing it for secretion.

The particular antigen to which an antibody will bind is determined by the composition of sugar groups attached to the antibody. This is because the sugar groups on the antibody form a unique pattern that allows the antibody to recognize and bind to specific antigens. The presence or absence of certain sugar groups can affect the shape and charge of the antibody, which in turn affects its ability to bind to antigens. Therefore, the composition of sugar groups plays a crucial role in determining the specificity of antibody-antigen interactions.