Final answer:
The incorrect statement about B-lymphocytes is that they are primarily involved in cell-mediated immunity. They produce antibodies and are a vital part of the humoral immune response, while cell-mediated immunity is mainly a function of T-lymphocytes.
Step-by-step explanation:
The statement about B-lymphocytes that is not correct is number 4) They are primarily involved in cell-mediated immunity. B-lymphocytes, also known as B cells, are a type of white blood cell that are crucial for the adaptive immune response, particularly the humoral immune response. They originate and mature in the bone marrow, and their primary function is the production of antibodies, not the cell-mediated immunity which is mainly a role of T cells.
B cells are involved in humoral immunity, which deals with the production of antibodies that attack pathogens in the extracellular environment. T cells, on the other hand, are responsible for cell-mediated immunity, which involves the targeting and destruction of cells infected with intracellular pathogens. This fundamental difference between B cells and T cells underscores their distinct roles in the immune system.