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

Antibodies that act against a particular foreign substance are released by PLASMA CELLS. 

Plasma cells, otherwise known as plasma B cells are developed from an activated B cell. They are white blood cells that can secrete large amounts of antibodies but they are short-lived.  They are transported through the blood plasma and the lymphatic system.