Final answer:
VDJ recombination takes place during the Pro-B cell stage (option 4) of B cell development in the bone marrow, involving the rearrangement of V, D, and J gene segments to create diverse antibodies.
Step-by-step explanation:
VDJ recombination occurs during the developmental phase of Pro-B cells, which is answer option 4. This process is a part of the maturation of B cells, which take place in the bone marrow. These gene rearrangements happen during the early stages of B cell development when they are known as Pro-B cells, prior to the formation of pre-B cells and ultimately maturing into naïve B cells.
The rearrangement of Variable (V), Diversity (D), and Joining (J) segments results in the creation of a unique variable region for the B cell receptor, which allows the recognition of a diverse array of antigens. It's important to note that the DNA recombinase enzyme facilitates this process, enabling each B cell to have a distinct antibody profile capable of binding various antigens. After these maturation steps in the bone marrow, the naïve B cells proceed to the spleen for final stages of maturation before becoming fully mature B cells.
When comparing the maturation process of B cells to T cells, it is crucial to understand that while B cells mature entirely within the bone marrow, T cells leave the bone marrow as progenitor cells and mature in the thymus. Both processes involve a combination of positive and negative selections to ensure functional and non-self-reactive immune cells.