Which leukocyte is primarily involved in antibody-mediated immunity?

The B-lymphocyte plays a crucial role in antibody-mediated immunity, also known as humoral immunity. When B-lymphocytes encounter antigens, they undergo activation and differentiation into plasma cells, which are specialized for producing antibodies. These antibodies bind specifically to antigens, marking pathogens for destruction or neutralization, and play a critical role in the immune response against infections. This type of immunity is particularly effective against extracellular pathogens, such as bacteria and viruses present outside cells.

While Helper T cells support the activation and function of B cells, they do not produce antibodies themselves. Monocytes are involved in phagocytosis and can differentiate into macrophages or dendritic cells, but their primary role is not in antibody production. Cytotoxic T cells are primarily responsible for cell-mediated immunity by directly killing infected cells rather than producing antibodies. Thus, the B-lymphocyte is the key player in antibody-mediated immunity, distinguishing it from the other leukocytes mentioned.