Which step is involved in T-cell-independent B-cell activation?

T-cell-independent B-cell activation involves a direct response of B cells to certain antigens, particularly polysaccharide antigens, without the need for helper T cells. In this process, the binding of the antigen to the B cell receptor (BCR) leads to B cell proliferation. This means that the activated B cell divides and can differentiate into plasma cells, which produce antibodies, as well as memory B cells that are essential for long-term immunity.

The option stating that the B cell proliferates into memory cells reflects this critical step in T-cell-independent activation. Memory cells play a vital role in the immune system, enabling the body to respond more rapidly and effectively if the same antigen is encountered in the future.

In contrast, the other options pertain to processes associated with T-cell-dependent B-cell activation, which involves helper T cells and antigen processing. For instance, helper T cells binding to antigens and providing necessary signals for activation are key to T-cell-dependent processes, which do not apply to T-cell-independent B-cell activation.