Antibodies that act against a particular foreign substance are released by antibodies that act against a particular foreign substance are released by medullary cords plasma cells t lymphocytes lymph nodes

The correct answer is "plasma cells". 

Plasma cells are differentiated or mature B cells capable of producing antibodies against a particular foreign substance. B cells are stimulated to differentiate into plasma cells when it binds to two receptors of helper T cell; having the T cells "help" the B cells to differentiate to plasma cells. These T cells have the antigenic information passed to them by antigen presenting cells such as dendritic cells and these will be passed to the B cells and plasma cells will produce antibodies against this specific antigen.