Question

The first checkpoint in B-cell maturation:

a. involves a pre-BCR.
b. checks for functional rearrangement of the L-chain variable domain gene segments.
c. utilizes -microglobulin and VpreB attached to the heavy chain.
d. A & B
e. A, B & C

Answer 1

The first checkpoint in B-cell maturation involves a pre-BCR, checks for the functional rearrangement of the light chain variable domain gene segments, and employs lambda-microglobulin and VpreB with the heavy chain. This process ensures the functionality and diversity of BCR specificities. The correct answer is e. A, B & C.

Step-by-step explanation:

The first checkpoint in B-cell maturation is crucial for ensuring that the B cells have functional antigen-binding receptors. This checkpoint involves the presence of a pre-B cell receptor (pre-BCR), which signifies that the heavy chain has been successfully rearranged. For a positive selection, the pre-BCR checks the functionality of the heavy chain. Pre-B cell receptor is associated with lambda-microglobulin and VpreB, emulating the light chain before its actual rearrangement.

The next step in maturity involves assessing whether the light chain variable domain gene segments are functionally rearranged, which allows the B cell to produce a complete B cell receptor capable of binding to specific antigens. During this process, DNA recombinase plays a key role by excising and splicing gene segments to generate a diverse repertoire of BCR specificities. Ultimately, only B cells with properly structured BCRs move forward in maturation, whereas those with non-functional or self-reactive BCRs undergo negative selection.

Therefore, the first checkpoint in B-cell maturation involves a pre-BCR and checks for functional rearrangement of the light chain variable domain gene segments, utilizing lambda-microglobulin and VpreB attached to the heavy chain. The correct answer to the question 'The first checkpoint in B-cell maturation:' is e. A, B & C.

Answer 2

The first checkpoint in B-cell maturation involves the pre-BCR, checks for the functional rearrangement of the L-chain variable domain gene segments, and utilizes lambda-microglobulin and VpreB. Therefore, the correct answer is option e. A, B & C.

Step-by-step explanation:

The first checkpoint in B-cell maturation is crucial to ensure the functional rearrangement of the B-cell receptor (BCR) components. Specifically, this checkpoint involves a pre-B-cell receptor (pre-BCR).

A pre-BCR checks for functional rearrangement of the heavy chain variable domain gene segments. If the heavy chain is successfully rearranged and functional, the pre-BCR signals the B cell to proceed with light chain rearrangement. This maturation step ensures that each B cell has a unique variable region capable of binding different antigens, which is essential for the immune response.

Moreover, during this checkpoint, the non-polypeptide components λmicroglobulin and VpreB are attached to the heavy chain. These components are surrogate light chains that transiently associate with the heavy chain and form part of the pre-BCR complex.