Question XIII. Consider each numbered statement (133-140) concerning various immunological facts, concepts and terminology as a completely independent assertion. Using your knowledge, please, assess these statements as factually correct (= true, T) or incorrect (= false, F): 133. The 12/23 rule means that a diversity (D) segment is almost always included in the formation of the immunoglobulin heavy-chain V region. 134. Although antigen-antibody reactions occur via non-covalent bonds, they are by their nature irreversible. 135. The T-cell receptor-encoding genomic sequences in our circulating T cells are the same as those our parents carry in their T cells. 136. Alternative splicing of RNA is utilized by T cells to form the and chains of a T-cell receptor. 137. In generating a B-cell receptor gene, Vk segments sometimes join to Cl segments. 138. In generating a T-cell receptor gene, Va segments sometimes join to Cd segments. 139. The switch in constant region usage from IgM to another immunoglobulin class (= isotype switching) is always mediated by DNA rearrangements. 140. A major reason why one individual might mount a response against a specific self-peptide, while other individuals might not is that there are differences in peptide binding potential of different MHC molecules. Solution 133. The 12/23 rule means that a diversity (D) segment is almost always included in the formation of the immunoglobulin heavy-chain V region. False. Recombination only occurs between gene segments located on the same chromosome. It generally follows the rule that only a gene segment flanked by a RSS with a 12-base pair (bp) spacer can be joined to one flanked by a 23 bp spacer RSS. This is known as the 12/23 rule. Thus, for the heavy chain, a DH gene segment can be joined to a JH gene segment and a VH gene segment to a DH gene segment, but VH gene segments cannot be joined to JH gene segments directly, as both VH and JH gene segments are flanked by 23 bp spacers and the DH gene segments have 12 bp spacers on both sides . So it can be included but not always. 134. Although antigen-antibody reactions occur via non-covalent bonds, they are by their nature irreversible. False. They are reversible. 135. The T-cell receptor-encoding genomic sequences in our circulating T cells are the same as those our parents carry in their T cells. False, The genes for encoding T-cell receptor are rearranged and edited during T-cell development in the thymus so that each mature T cell carries a different T-cell receptor gene sequence. 136. Alternative splicing of RNA is utilized by T cells to form the and chains of a T-cell receptor. False.

1. Question XIII. Consider each numbered statement (133-140) concerning various immunological
facts, concepts and terminology as a completely independent assertion. Using your knowledge,
please, assess these statements as factually correct (= true, T) or incorrect (= false, F):
133. The 12/23 rule means that a diversity (D) segment is almost always included in the
formation of the immunoglobulin heavy-chain V region.
134. Although antigen-antibody reactions occur via non-covalent bonds, they are by their nature
irreversible.
135. The T-cell receptor-encoding genomic sequences in our circulating T cells are the same as
those our parents carry in their T cells.
136. Alternative splicing of RNA is utilized by T cells to form the and chains of a T-cell
receptor.
137. In generating a B-cell receptor gene, Vk segments sometimes join to Cl segments.
138. In generating a T-cell receptor gene, Va segments sometimes join to Cd segments.
139. The switch in constant region usage from IgM to another immunoglobulin class (= isotype
switching) is always mediated by DNA rearrangements.
140. A major reason why one individual might mount a response against a specific self-peptide,
while other individuals might not is that there are differences in peptide binding potential of
different MHC molecules.
Solution
133. The 12/23 rule means that a diversity (D) segment is almost always included in the
formation of the immunoglobulin heavy-chain V region.
False.
Recombination only occurs between gene segments located on the same chromosome. It
generally follows the rule that only a gene segment flanked by a RSS with a 12-base pair (bp)
spacer can be joined to one flanked by a 23 bp spacer RSS. This is known as the 12/23 rule.
Thus, for the heavy chain, a DH gene segment can be joined to a JH gene segment and a VH
gene segment to a DH gene segment, but VH gene segments cannot be joined to JH gene
segments directly, as both VH and JH gene segments are flanked by 23 bp spacers and the DH
gene segments have 12 bp spacers on both sides . So it can be included but not always.
134. Although antigen-antibody reactions occur via non-covalent bonds, they are by their nature
irreversible.
False. They are reversible.
135. The T-cell receptor-encoding genomic sequences in our circulating T cells are the same as

2. those our parents carry in their T cells.
False, The genes for encoding T-cell receptor are rearranged and edited during T-cell
development in the thymus so that each mature T cell carries a different T-cell receptor gene
sequence.
136. Alternative splicing of RNA is utilized by T cells to form the and chains of a T-cell
receptor.
False