Types Of Immunity

Plasma cells are fully differentiated -lymphocytes. They are main antibody synthesizing cells of the body. Plasma cells respond to antigens by secreting antibodies into the blood and lymph. Because antibodies are soluble in blood, lymph, and other extracellular fluids, they provide humoral (latin, homour, a liquid) immunity or antibody- mediated immunity.

So, the correct answer is (A): B-lymphocyte