Final answer:
The expression of a pre-B cell receptor on the cell surface primarily leads to the proliferation of the B cell within the bone marrow. It is a critical step in the positive selection of B cells with functional antigen receptors, unlike T cells which undergo maturation in the thymus after leaving the bone marrow.
Step-by-step explanation:
As soon as a pre-B cell receptor (pre-BCR) is expressed on the cell surface, the primary event that occurs is b) Proliferation, although it is not explicitly listed among the options provided in the question. Once the pre-BCR is successfully expressed, the developing B cell receives a signal to proliferate and continue its maturation process in the bone marrow. This initial expression and signaling are essential for the positive selection process of B cells which have functional antigen-binding receptors. The proliferation of B cells is crucial for maintaining a diverse pool of B cells to respond to the plethora of antigens an organism may encounter.
By contrast, differentiation into T cells and exit from the bone marrow occur at different stages of immune cell maturation. CD4+T cell precursors are formed in the bone marrow but then migrate to the thymus, where they develop their T cell receptors (TCRs) and mature into naïve T cells. On the other hand, the negative selection process in the thymus leads to the destruction of immature T cells that express TCRs complementary to self-antigens, preventing autoimmune responses.