<prompt> Circulating antibodies formed by?T-cellsB-cellsMacrophagesPlasma cells  <response>: Ans. is d i.e., Plasma cells Plasma cells are the antibody secreting cells. On contact with its appropriate antigen, the mature B cell undergoes clonal proliferation. The majority of activated B cells are transformed into plasma cells and secrete antibodies While plasma cell is the best antibody producing cell, lymphocytes, lymphoblasts and transitional cells may also synthesise Ig to some extent 